ALBERT

Notes: The equilibrium thermodynamics of the reaction:And the equilibrium constant is composed of activities formulated using ideal mixing on sites. Consideration is given to the evaluation of uncertainties in pressures calculated using the geobarometer. Preliminary testing suggests that the geobarometer has considerable potential. Much wider testing is now required.

Notes: Abstract. Pink piemontite-spessartine-bearing and grey-green spessartine-bearing manganiferous quartzose schists derived from siliceous pelagites, and green quartzofeldspathic schists, are described from the greenschist facies of the Haast Schist terrane, near Arrow Junction, western Otago. Electron microprobe data are reported for sphene, spessartine-rich garnet, manganoan epidote, piemontite, tourmaline, phengitic muscovite, chlorite, albite, haematite, rutile, manganoan calcite and chalcopyrite.Metamorphism occurred at about 6.4kbar, 400°C. Xco2 was above the quartz-rutile-calcite-sphene buffer (Xco2± 0.02) throughout the recorded metamorphic history of the piemontite schists. It dropped from above to below this critical buffering value in a spessartine-rich schist and it was close to or below the buffering value in the quartzofeldspathic schists. Production of piemontite required high fO2, believed to be inherited from MnOx in the parent pelagite. Substantial loss of O2 (e.g. minimum of 0.19% by weight in one rock) during diagenesis and/or metamorphism is inferred. In the grey-green schists this inhibited piemontite formation. Slight loss of O2 and Ca2+ accompanied minor late-stage replacement of piemontite by second generation spessartine. Observed zoning and mineral replacements indicate rise of temperature, drop in pressure, or invasion by solutions of lower fO2 and XCO2 equilibrated with surrounding schists.The detailed chemistry of the minerals studied correlates with available Mn and with bulk-rock (Fe3+ x 100)/(Fe2++ Fe3+). The oxidation ratio ranges from 24 in average green quartzofeldspathic schist, through 78 in average grey-green manganiferous quartzose schist, to almost 100 in some piemontite-bearing schists. As Fe2+ gives way to Fe3+, Mg/Fe ratios tend to rise in chlorite, phengite, tourmaline, spessartine, and calcite, Mn increases and Ti decreases in haematite, Mn increases in spessartine and calcite, and Fe increases in rutile. Available divalent cations are depleted relative to Al; chlorite is more aluminous, and phengite more paragonitic than in typical Haast schists.

Notes: CO2–CH4 fluid inclusions are present in anatectic layer-parallel leucosomes from graphite-bearing metasedimentary rocks in the Skagit migmatite complex, North Cascades, Washington. Petrological evidence and additional fluid inclusion observations indicate, however, that the Skagit Gneiss was infiltrated by a water-rich fluid during high-temperature metamorphism and migmatization.CO2-rich fluid inclusions have not been observed in Skagit metasedimentary mesosomes or melanosomes, meta-igneous migmatites, or unmigmatized rocks, and are absent from subsolidus leucosomes in metasedimentary migmatites. The observation that CO2-rich inclusions are present only in leucosomes interpreted to be anatectic based on independent mineralogical and chemical criteria suggests that their formation is related to migmatization by partial melting. Although some post-entrapment modification of fluid inclusion composition may have occurred during decompression and deformation, the generation of the CO2-rich fluid is attributed to water-saturated partial melting of graphitic metasedimentary rocks by a reaction such as biotite + plagioclase + quartz + graphite ± Al2SiO5+ water-rich fluid = garnet + melt + CO2–CH4. The presence of CO2-rich fluid inclusions in leucosomes may therefore be an indication that these leucosomes formed by anatexis.Based on the inferences that (1) an influx of fluid triggered partial melting, and (2) some episodes of fluid inclusion trapping are related to migmatization by anatexis, it is concluded that a free fluid was present at some time during high-temperature metamorphism. The infiltrating fluid was a water-rich fluid that may have been derived from nearby crystallizing plutons. Because partial melting took place at pressures of at least 5 kbar, abundant free fluid may have been present in the crust during orogenesis at depths of at least 15 km.

Notes: The solid-solid reaction magnesiocarpholite = sudoite + quartz has been bracketed between 350 and 500°C, 6.3 and 7.8 kbar. Because it is impossible to synthesize end-member sudoite, all experiments were carried out using natural minerals as starting materials. Although mineral compositions were very close to those of the end-members, the effect of the fluorine content in carpholite was significant. Particularly in those experiments where sudoite grows at the expense of carpholite, electron microprobe analysis of the run products shows that a more stable F-rich carpholite crystallizes too, and consumes the fluorine released in solution by the breakdown of the original carpholite.Our experimental results are combined, through a thermodynamic analysis, with a previous data set and with previous experimental data concerning the relative stability of chlorite, talc and magnesiocarpholite with excess of quartz and water as a function of P–T and AlAl(SiMg)-1 substitutions in phyllosilicates. This allows us to constrain the feasible thermodynamic parameters (H°f, sud; S° sud) and (H°f,car; S°car) for the Mg end-members. Using the partition coefficients calculated from natural parageneses, we have computed a petrogenetic grid for the system FeO–MgO–Al2O3–SiO2–H2O. It demonstrates that parageneses involving sudoite and carpholite can be used as indicators of P–T conditions, up to 600° C, 8 kbar for sudoite, and at higher pressure for carpholite.

Notes: Regional-scale mapping of index-mineral isograds in mafic units of the early Proterozoic Cape Smith Thrust Belt (northern Québec) has revealed contrasting pressure-temperature regimes associated with two distinct structural domains. In the southern domain, crustal thickening was accomplished by early, piggy-back thrust faults. Isograds cross-cut the thrusts, indicating that thermal-peak mineral growth outlasted deformation associated with early imbrication. Mineral zones are: (1) actinolite (Act) + albite (Alb); (2) hornblende (Hbl) + Act + Alb; (3) Hbl + Act + oligoclase (Oli); (4) Hbl + Oli; and (5) garnet (Grt) or clinopyroxene + Hbl + Oli-andesine. The oligoclase isograd occurs at higher grade than the hornblende isograd, a sequence typical of medium-pressure terranes (5–7 kbar). An Hbl-Alb bathograd. calibrated from mixed-volatile equilibria in the NCMASH-CO2 model system, suggests minimum pressures of about 5.4 kbar.Metamorphism in the northern domain was a consequence of re-imbrication, by means of out-of-sequence thrust faults active during and after peak metamorphic conditions. Mineral growth was coeval with thrusting, as documented by the syn-kinematic garnet porphyroblasts. Compared to the southern domain, a different sequence of isograds in mafic rocks shows that the albite-oligoclase transition takes place in the garnet zone. Based on thermobarometry in garnet-hornblende rocks, the oligoclase isograd occurs in a temperature range of 525–600°C, typical of high-pressure terranes (7–10 kbar). Calibrated bathograds for the Hbl-Ms-Alb and Grt-Alb bathozonal assemblages, respectively in the KNCMASH-CO2 and NCMASH model systems, indicate minimum pressures in the northern domain of 6.7 and 8.5 kbar. Higher-pressure series for this domain are explained by out-of-sequence thrusts exposing deeper crustal levels. For similar structural levels, only minor amounts of syn-deformational uplift (1–2 kbar and 50–75°C) are recorded in metabasites of this domain, compared to results in adjacent metapelites of the area (essentially isothermal uplift of 3–5 kbar).RESUME La bande du Cap Smith (nord du Québec) est une ceinture de chevauchement d'ǎge protérozoique inférieur, dominée par des roches mafiques. La cartographie d'isogrades à minéraux indicateurs dans les unités mafiques de la ceinture a révelé deux régimes contrastes de pression–température, chacun associéà des épisodes distincts d'épaississement crustal. Dans le domaine sud, des failles de chevauchement en-série sont responsables pour l'empilement tectonique. Les isogrades recoupent les failles, indiquant que l'apogée thermale a suivi l'emplacement initial des nappes de charriage. Les zones minérales sont: (1) actinote (Act) + albite (Alb); 2) hornblende (Hbl) + Act + Alb; (3) Hbl + Act + oligoclase (Oli); 4) Hbl + Oli; et (5) grenat (Grt) où clinopyroxene + Hbl + Oli-andésine. L'isograde d'oligoclase apparaǐt à plus haute température que l'isograde d'hornblende, une séquence typique des terrains de pressions moyennes. Un bathograde Hbl–Alb, calibréà partir d'équilibre mixte de volatiles dans le système NCMASH–CO2, suggère des pressions minimales d'environ 5.4 kbar.Le métamorphisme dans le domaine nord de la ceinture a été le résultat d'une réimbrication, causé par des chevauchements hors-série actifs pendant et après l'apogée thermale. La croissance minérale fǔt synchrone au chevauchement, documentée par des porphyroblastes de grenat syn-cinénatique. Comparé au domaine sud, une différente séquence d'isogrades dans les métabasaltes montre que la transition albite–oligoclase se situé dans la zone à grenat. Par la thermobarométrie dans les roches à grenat–hornblende l'isograde d'oligoclase se situe dans un écart de température de 525–600°C, typique des terrains de hautes pressions (7–10 kbar). Des bathogrades calibrés pour les assemblages bathozonales Hbl–Ms–Alb et Grt–Alb, rcspectivement dans les systèmes KNCMASH–CO2 et NCMASH, indique des pression minimales pour le domaine nord de 6.7 et 8.5 kbar. Une zonégraphie à plus haute pression pour ce domaine est expliquée par des chevauchements hors-série exposant des niveaux plus inférieurs de la croǔte imbriqué. Pour des niveaux structuraux similaries, des soulèvements syn-métamorphiques mineurs sont enregistrés dans les métabasaltes (1–2 kbar et 50–75°C), comparés aux métapélites adjacentes avec un soulèvement (essentially isothermal uplift of 3–5 kbar.

Notes: Mid-Cretaceous granulite gneisses crop out in a narrow belt in the Cucamonga region of the south-eastern foothills of the San Gabriel Mountains, southern California. Interlayered mafic granulites and pelitic, carbonate, calc-silicate and quartzofeldspathic metasediments record hornblende granulite subfacies metamorphism at approximately 8 kbar and 700–800°C. Regional deformation and formation of banded gneisses ceased by c. 108 Ma. although mafic-intermediate magmatism and high-grade metamorphism continued locally as late as c. 88 Ma. Garnet zoning in metapelitic gneisses suggests that peak metamorphism was followed locally by a period of near-isobaric cooling, but this interpretation requires diachronous cooling of the granulite belt which cannot be demonstrated without detailed thermo-chronological data. It is more likely that the entire terrane remained at granulite facies P–T conditions until 88 Ma, followed by rapid uplift associated with juxtaposition against adjacent middle and upper crustal arc terranes. Uplift occurred between c. 88 and 78 Ma at rates of approximately 1–2 km Ma-1. The geotectonic evolution of the Cucamonga granulites is similar to mid-Cretaceous high-P granulites in the Sierra Nevada and Salinian block of central California. Late Cretaceous uplift common to these granulites may provide an important tectonic link between dismembered Mesozoic batholithic terranes in the California Cordillera.

Notes: Field, petrographic and microprobe investigations of metaclastic rocks, calcareous schists, marbles, chloritic calcareous meta-volcanic units and schists/paragneisses which crop out along the eastern portion of the Central East-West Cross Island Highway in Taiwan demonstrate that metamorphic intensity gradually increases eastward. The lower greenschist facies Slate Formation on the W contains completely recrystallized, pure albitic plagioclase, but at least some of the white micas (± chlorites) probably represent relict detrital flakes. Neo-blastic biotite and epidote occur sporadically in the Pihou(?) Formation, and increase dramatically eastward; concomitantly the abundance of carbonaceous matter decreases to zero in the eastern Tailuko zone, and the amount of chlorite + white mica diminishes somewhat. Epidote becomes more aluminous at higher metamorphic grade. Eastward, phengites change progressively to more muscovitic compositions as the proportion of biotite increases.A close approach to chemical equilibrium for the pre-Cenozoic, complexly deformed metamorphic basement assemblages is suggested by regular, systematic, major and minor element partitioning between analysed coexisting phases. Fractionation is less pronounced on the E, reflecting higher temperatures. Estimated physical conditions of recrystallization with αH2O and αCO2 moderate, are: T 〉 325 ± 75°C, P 〉 3 kbar (W); T 〉 425 ± 75°C, P 〉 4kbar(E).The gradual eastward increase in metamorphic intensity from the Slate Formation through the Pihou(?) Formation and the three Tailuko zones, as well as the relict precursor textures in the pre-Cenozoic layered basement rocks indicate that the observed paragenetic sequence could represent a synchronous Neogene recrystallization event, probably accompanying the Plio-Pleistocene collision of the Asiatic continental margin and the Luzon (Coastal Range) andesitic arc.

Notes: The structure, microstructure and petrology of a small area close to the village of Bard in Val d'Aosta (Italy) has been studied in detail. The area lies across the contact between the Gneiss Minuti (GM) and the Eclogitic Micaschist (EMS) Complexes of the Lower element of the Sesia portion of the Sesia-Lanzo Zone (Western Alps). Both complexes have undergone high-pressure metamorphism, but the metamorphic assemblages indicate a sudden increase in pressure in going across the contact from the GM to the EMS. Therefore, we interpret the contact as a thrust dividing the lower element of the Sesia into two sub-elements. This interpretation is supported by structural evidence.The early Alpine (90-70 Ma) metamorphic history is best preserved in the EMS and is one of increasing pressure associated with thrusting. The maximum P/T recorded in the EMS is 〉1500 MPa (〉15kbar) and 550°C and in the GM is 〈 1500-1300 MPa (〈 15-13 kbar) and 500-550°C. We suggest that the rocks were probably in an active Benioff zone during this time.From then on the histories of the GM and EMS are the same. Deformation continued and the thrust and thrust slices were folded during decreasing pressure. We interpret the first postthrusting deformation in terms of uplift associated with continued shortening of the crust and underplating after the Benioff zone had become inactive and a new Benioff zone had developed further to the north-west.A still later deformation and the Lepontine metamorphism (38 Ma) are related to continued uplift. Much of this deformation is characterized by structures indicative of vertical shortening and lateral spreading as the mountains rose above the general level of the surface.

Notes: In the Boi Massif of Western Timor the Mutis Complex, which is equivalent to the Lolotoi Complex of East Timor, is composed of two lithostratigraphical components: various basement schists and gneisses; and the dismembered remnants of an ophiolite. Cordierite-bearing pelitic schists and gneisses carry an early mineral assemblage of biotite + garnet + plagioclase + Al-silicate, but contain no prograde muscovite; sillimanite occurs in a textural mode which suggests that it replaced and pseudomorphed kyanite at an early stage and some specimens of pelitic schist contain tiny kyanite relics in plagioclase. Textural relations between, and mineral chemistries of, ferro-magnesian phases in these pelitic chists and gneisses suggest that two discontinuous reactions and additional continuous compositional changes have been overstepped, possibly with concomitant anatexis, as a result of decrease in Pload during high temperature metamorphism. The simplified reactions are: garnet and/or biotite + sillimanite + quartz + cordierite + hercynite + ilmenite + excess components. P-T conditions during the development of the early mineral assemblage in the pelitic gneisses are estimated to have been P + 10 kbar and T 〉 750°C, based upon the plagioclase-garnet-Al-silicate-quartz geobarometer and the garnet-biotite geothermometer. P-T conditions during the subsequent development of cordierite-bearing mineral assemblages in the pelitic gneisses are estimated to have been P + 5 kbar and T + 700°C with XH2O 〈 0.5, based upon the Fe content of cordierite occurring in the assemblage quartz + plagioclase + sillimanite + biotite + garnet + cordierite coexisting with melt.Final equilibration between some of the phases suggests that conditions dropped to P 〉 2.3 kbar and T 〉 600°C. A similar exhumation P-T path is suggested for the pelitic schists with early metamorphic conditions of P 〉 6.2 kbar and T 〉 745°C and subsequent development of cordierite under conditions in the range P = 3-4 kbar and T = 600-700°C. The tectonic implications of these P-T estimates are discussed and it is concluded that the P-T path followed by these rocks was caused by decompression during rifting and synmetamorphic ophiolite emplacement resulting from processes during the initiation and development of a convergent plate junction located in Southeast Asia during late Jurassic to Cretaceous time.

Notes: Plagioclase compositions vary from An0.1–2.5 to An32 with increasing grade in chlorite zone to oligoclase zone quartzofeldspathic schists, Franz Josef-Fox Glacier area, Southern Alps, New Zealand. This change is interrupted by the peristerite composition gap in rocks transitional between greenschist and amphibolite facies grade. Oligoclase (An20-24) and albite (An0.1–0.5) are found in biotite zone schists below the garnet isograd. With increasing grade, the plagioclase compositions outline the peristerite gap, which is asymmetric and narrows to compositions of An12 and An6 near the top of the garnet zone. In any one sample, oligoclase is the stable mineral in mica-rich layers above the garnet isograd, whereas albite and oligoclase exist in apparent textural equilibrium in adjacent quartz-plagioclase layers. The initial appearance of oligoclase in both layers results from the breakdown of epidote and possibly sphene. Carbonate is restricted to the quartz-plagioclase rich layers and probably accounts for the more sodic composition of oligoclase in these layers. The formation of more Ca-rich albite and more Na-rich oligoclase near the upper limit of the garnet zone coincides with the disappearance of carbonate and closure of the peristerite gap. Garnet appears to have only a localized effect on Ca-enrichment of plagioclase in mica-rich layers within the garnet zone. The Na-content of white mica increases sympathetically with increasing Ca-content of oligoclase and metamorphic grade.Comparison of the peristerite gap in the Franz Josef-Fox Glacier schists and schists of the same bulk composition in the Haast River area, 80 km to the S, indicates that oligoclase appears and epidote disappears at lower temperatures, and that the composition gap between coexisting albite and oligoclase is narrower in the Franz Josef-Fox Glacier area. It is suggested that a higher thermal gradient (38-40°C/km) and variations in Si/Al ordering during growth of the plagioclases between the two areas may account for these differences. In the Alpine schists the peristerite gap exists over a temperature and pressure interval of about 370-515°C and 5.5-7 kbar (550-700 MPa) PH2O.

Notes: In this paper we analyze the properties of price equilibria in a duopoly market where firms sell vertically differentiated products, consumers being uncertain about which firm sells which quality. Both existence and properties of price equilibria are characterized by the beliefs of the consumers' population about the distribution of quality between firms.

Notes: The survey classifies economic theories of the firm into four categories based on the level of aggregation in economic models: (1) neoclassical, (2) industrial organization, (3) contractual, and (4) organizational incentive. Economic theories of the firm are evaluated on the basis of their potential application to problems of management decision making. The survey suggests that a management perspective can be useful in developing an integrated theoretical analysis of the firm that addresses both competitive strategy and organizational design.

Notes: Commitment: The Dynamic of Strategy, by Pankaj Ghemawat.Ghemawat's Commitment makes recent results in game-theoretic industrial organization accessible and useful to practitioners in the field of strategic management. This book contributes to the management strategy literature on two levels. On a conceptual level, Ghemawat strives to isolate “commitment” as the sole explanation of persistent differences in firm performance. On a more pragmatic level, he provides a framework intended to aid managers in making commitment-intensive decisions. It is with respect to how well he achieves these two distinct goals that I evaluate Ghemawat's contribution. In addition, I review briefly the book's content, and I compare Ghemawat's approach to some alternative approaches familiar to scholars and practitioners of strategic management.

Notes: In the present paper, we relate the extent of job security offered to incumbent managers to the extent of competition among firms in the product market, where the extent of job security is measured by the probability that an incumbent manager continues to be employed by his current firm and the extent of competition is measured by the degree of differentiation between competing brands. We demonstrate that when competition between firms intensifies and “on-the-job training” is relatively more conducive to reducing the variable costs of production, firms tend to offer reduced (increased) job security to incumbent managers, provided that the degree of differentiation between competing products is sufficiently large (small), respectively. If “on-the-job training” is relatively more conducive to reducing the fixed costs of production, however, the previous result is reversed.

Notes: This paper presents a model of strategic product choice when consumer preferences combine features of both horizontal and vertical product differentiation. Consumers disagree on what amount of a “special” characteristic makes for a better product, but those who prefer more of this attribute are willing to pay more for it. Within this demand structure, I examine the advantages of first-mover firms. I find that such firms typically do best in markets where the maximum degree of product differentiation is limited by preferences rather than technology. These are “niche markets”. Follower firms do better in markets in which the range of preferences is broad relative to the span of feasible goods.

Notes: This paper reexamines Grossman and Hart's (1980) insight into how the free-rider problem excludes an external raider from capturing the increase in value it brings to R firm The inability of the raider to capture any of the surplus depends critically on the assumption of equal and indivisible shareholdings–the one-share-per-shareholder model In contrast, we show that once shareholdings are large and potentially unequal, a raider may capture a significant part of the increase in value Specifically, the free-rider problem does not prevent the takeover process when shareholdings are divisible.

Notes: We analyze the implementation problem faced by firms when trying to collude in the face of asymmetric information about costs. Assuming that transfer payments are possible, we examine the incentive compatibility and individual rationality constraints that must be satisfied by any cartel agreement. Two scenarios are considered. Firms may or may not withdraw from the agreement after each firm's costs become known. If no withdrawal is possible, we find that the monopoly rule is implementable when weak types of individual rationality constraints are required. This contrasts with some results in the literature. If withdrawal is possible, we find a potential conflict between different forms of individual rationality constraints, in particular, between interim and ex post constraints. This conflict disappears in industries with a large number of firms.

Notes: This paper offers a general characterization of the optimal product line prices for a monopolist whose quality of products is initially unknown to consumers. In the focal equilibrium, a monopolist signals a high-quality product line by pricing as if quality were known to be high, but costs of production were higher than they truly are. In a rich set of environments, this characterization implies that the prices of all products are initially distorted upward, with the price distortion being largest for products with the most inelastic demands and/or quality-sensitive production costs. These implications yield predictions for the time path of prices flint are broadly consistent with evidence from the marketing literature. The multidimensional signaling problem is made tractable by the satisfaction of a very simple and powerful single crossing property.

Notes: Managerial behavior that is rational and profit-maximizing sometimes will seem to be overly conservative. If the valuation of innovations contains white noise and the status quo would be preferred to random innovation, then any innovation that does not appear substantially better than the status quo should be rejected, for reasons arising from regression toward the mean. The more successful the firm, the higher is the optimal acceptance threshold and conservative bias. Other things equal, more successful firms will spend less on research, adopt fewer innovations, and be less likely to advance the industry's best practice.

Notes: Identical cases of wine are often auctioned one immediately after another. Ashenfelter (1989) reports that on average, the later lots fetch less. Such a systematic price difference seems anomalous, the more so because it is shown here that rational expectations imply not equal, but rising, prices. Risk aversion is an obvious way of reconciling the evidence with rational behavior. There is an alternative explanation. The auctions observed by Ashenfelter involved a buyer's option, whereby the first-round winner could purchase further cases at the same price. It is shown that this feature may both account for the observed price trajectory and raise seller revenue.

Notes: This paper examines the incentives for integration when the market for consumer durables (hardware) is oligopolistic and the market for complementary services (software) is monopolistically competitive. We find that the equilibrium industry structure will depend on the magnitude of the fixed costs of software development. If the software development costs are relatively large, the equilibrium industry structure is unintegrated, that is, neither hardware firm integrates; if the software development costs are relatively small, the equilibrium industry structure is integrated, that is, both hardware firms integrate. Under the integrated industry structure, hardware profits are lower, less varieties are provided, and hardware prices are lower than under the unintegrated industry structure. The game has a prisoners' dilemma structure when the software development costs are relatively small because of a foreclosure effect. Strategically increasing the number of software varieties provides an avenue for an integrated hardware firm to increase its market share and profits by reducing the number of software varieties available for an unintegrated rival technology. Although consumer surplus is higher under an integrated industry structure, the total surplus associated with the unintegrated industry structure exceeds that of the integrated industry structure.

Notes: Price setting by firms and search by customers is analyzed, relaxing two basic attributes of most search models: price precommitment and agent heterogeneity. Customers are characterized by individual demand functions for a homogeneous good and can choose to employ a threat to search. Firms noncooperatively make pricing decisions by using the individual demand curves under conditions of constant marginal cost. Firms adopt pricing rules that optimally respond to customer search histories. Bargaining power is endogenously assigned. Firms know their common marginal cost; customers, the cost distribution. The unique separating equilibrium is characterized by a lumpy distribution of prices and by heterogeneous shopping behavior by customers giving rise to “shoppers” and “nonshoppers”

Notes: Most research on product positioning supports the idea of differentiation. Product standardization (i.e., minimum differentiation) occurs only under very limiting assumptions. Yet, similar products are often observed in the marketplace. We attempt to restore the case for standardization by using more realistic assumptions than in previous work. We assume that consumers consider not only observable attributes in brand choice, but also attributes that are unobservable by the firms. We find that standardization is an equilibrium when consumers exhibit sufficient heterogeneity along the unobservable attributes under both positioning with exogenously given prices and price competition, We also show that, under insufficient heterogeneity along the unobservable attribute, our results coincide with past research that argues in favor of differentiation.

Notes: This paper proposes an empirical methodology for studying various (implicit or explicit) collusive behaviors on two strategic variables, which are price and advertising, in a differentiated market dominated by a duopoly. In addition to Nash or Stackelberg behaviors, we consider collusion on both variables, collusion on one variable and competition on the other, etc. Using data on the Coca-Cola and Pepsi-Cola markets from 1968 to 1986, full information maximum likelihood estimation of cost and demand functions are obtained allowing for various collusive behaviors. The collusive hypothesis is not rejected, and the best form of collusive behavior is selected via nonnested testing procedures. Using the best model, Lerner indices are computed for both duopolists to provide summary measures of market power. Finally, our approach is contrasted with the conjectural variation approach and is shown to give superior results.

Notes: The Whitestone Anorthosite (WSA), located in southern Ontario, underwent granulite facies metamorphism during the Grenville orogeny at 1.16 Ga. During the waning stages of metamorphism fluids infiltrated the outer portions of the anorthosite and promoted the formation of an envelope comprised of upper amphibolite facies mineral assemblages. Also, this envelope corresponds to portions of the anorthosite that underwent deformation related to movement along a high-grade ductile shear zone. Samples from this portion of the anorthosite (the margin) contain CO2-rich inclusions in plagioclase porphyroclasts (relict igneous phenocrysts), matrix plagioclase and garnet. These inclusions have features which normally are interpreted as indicating that they are texturally primary, but they have relatively low CO2 densities (0.61–0.95 g cm-3). Plagioclase from the anorthosite interior contains texturally secondary inclusions with relatively high CO2 densities (generally from 0.99 to 1.10 g cm-3). The high CO2 densities suggest that the inclusions in the plagioclase of the anorthosite core formed prior to inclusions in porphyroclast minerals of the outer portions of the anorthosite, an interpretation that is apparently inconsistent with inclusion textures. This apparent paradox indicates that most fluid inclusions from the anorthosite margin were formed during, or were modified by, the dynamic recrystallization that affected this portion of the WSA. In either case, late formation or modification, the texturally primary fluid inclusions do not contain pristine samples of the peak metamorphic fluid. Furthermore, because shear-related deformation is apparently associated with entrapment of the lowest fluid densities, some strain localization persisted to relatively low temperatures (e.g. less than approximately 500° C). These results constrain a part of the retrograde P–T path for this portion of the Grenville Orogen to temperatures of approximately 400–500° C at pressures of approximately 1–2 kbar.

Notes: A suite of metapelites, charnockites, calc-silicate rocks, quartzo-feldspathic gneisses and mafic granulites is exposed at Garbham, a part of the Eastern Ghats granulite belt of India. Reaction textures and mineral compositional data have been used to determine the P–T–X evolutionary history of the granulites. In metapelites and charnockites, dehydration melting reactions involving biotite produced quartzofeldspathic segregations during peak metamorphism. However, migration of melt from the site of generation was limited. Subsequent to peak metamorphism at c. 860° C and 8 kbar, the complex evolved through nearly isothermal decompression to 530–650° C and 4–5 kbar. During this phase, coronal garnet grew in the calc-silicates, while garnet in the presence of quartz broke down in charnockite and mafic granulite. Fluid activities during metamorphism were internally buffered in different lithologies in the presence of a melt phase. The P–T path of the granulites at Garbham contrasts sharply with the other parts of the Eastern Ghats granulite belt where the rocks show dominantly near-isobaric cooling subsequent to peak metamorphism.

Notes: Staurolite porphyroblasts, 1.5–8cm in length and 0.3–2cm in width, in the Littleton Schist at Bolton, Connecticut, contain curved quartz inclusion trails which document synkinematic rotations of at least 135°. The orientations of long axes of these staurolite crystals define a weak preferred orientation in a plane approximately parallel to the external foliation. Serial sections of four differently orientated crystals and U-stage measurements of the orientations of their inclusion trails demonstrate that the inflection hinge line and the statistical ‘symmetry axis’ characterizing the foliation within a porphyroblast are unrelated to the orientations of external crenulations and are, in all cases, parallel to the long axis of the porphyroblast. The cumulative rotation reflected in the curvature of the inclusion trails is a maximum in a c-axis section through the initial core of a crystal. The amount of rotation about the c-axis decreases linearly along the length of the crystal away from the nucleation site.The sense and amount of rotation recorded by a porphyroblast is related to its orientation. A tightly constrained transition from clockwise to anticlockwise rotation defines a slip direction that coincides with the preferred orientation of the staurolite c-axes. The total rotation reflected by the inclusion trails increases as a function of the angle between the c-axes of the staurolite crystals and the slip direction.Initially random staurolite porphyroblasts rotated during growth, as a consequence of laminar shear in the surrounding viscous matrix. This interpretation is quantitatively consistent with: the staurolite preferred orientation; its coincidence with the apparent slip direction; the correlation between both the sense and the amount of rotation and the orientation of the long axis of the porphyroblast; and the twisted conical shape of the family of surfaces defined by the inclusion trails.

Notes: Silica-deficient sapphirine-bearing rocks occur as an enclave within granulite facies Proterozoic gneisses and migmatites near Grimstad in the Bamble sector of south-east Norway (Hasleholmen locality). The rocks contain peraluminous sapphirine, orthopyroxene, gedrite, anthophyllite, sillimanite, sapphirine, corundum, cordierite, spinel, quartz and biotite in a variety of assemblages. Feldspar is absent.Fe2+/(Fe2++ Mg) in the analysed minerals varies in the order: spinel 〉 gedrite ≥ anthophyllite ≥ biotite 〉 sapphirine〉orthopyroxene 〉 cordierite.Characteristic pseudomorph textures indicate coexistence of orthopyroxene and sillimanite during early stages of the reaction history. Assemblages containing orthopyroxene-sillimanite-sapphirine-cordierite-corundum developed during a high-pressure phase of metamorphism and are consistent with equilibration pressures of about 9 kbar at temperatures of 750–800°C. Decompression towards medium-pressure granulite facies generated various sapphirine-bearing assemblages. The diagnostic assemblage of this stage is sapphirine-cordierite. Sapphirine occurs in characteristic symplectite textures. The major mineralogical changes can be described by the discontinuous FMAS reaction: orthopyroxene + sillimanite → sapphirine + cordierite + corundum.The disequilibrium textures found in the Hasleholmen rocks are characteristic for reactions which have been in progress but then ceased before they run to completion. Textures such as reaction rims, symplectites, partial replacement, corrosion and dissolution of earlier minerals are characteristic of granulite facies rocks. They indicate that, despite relatively high temperatures (700–800° C), equilibrium domains were small and chemical communication and transport was hampered as a result of dry or H2O-poor conditions.

Notes: The Vredefort dome (2.0 Ga) represents the central uplift of a very large impact structure. This uplift exposed a nearly complete cross-section through the continental crust in the region, which is 25–30 km thick. Two metamorphic events took place at about the same time as the impact. The first event, so-called static metamorphism, is pre-impact and produced lithologies varying from low-grade shale to high-grade hornfels. It resembles contact metamorphism by its lack of schistosity, but is more regional as it extends over a large area and is not associated with large intrusions.The second event, the post-shock metamorphism, is responsible for the recrystallization of the shock features. The investigation of this event has been focused on the degree of alteration of the coesite-stishovite-bearing pseudotachylite veins that formed during the transit of the shock wave. These high-pressure silica polymorphs are only present in the upper part of the stratigraphic sequence; downward they have been converted to fibrous quartz. At the highest grade, the fibrous quartz is in turn replaced by triple-junctioned mosaic quartz. The post-shock metamorphism was generated by the heat of the rock before shock, plus the heat released by the shock wave. The isograds, plotted on a map, can be translated into depth of burial and therefore provide valuable information regarding the geological setting immediately before impact. At the time of impact, the rocks were relatively cool and the static metamorphism had ceased with several tens of millions of years separating the two metamorphic events. The static metamorphism was probably caused by continental crustal extension in a stress-free environment and the lack of deformation is probably due to rapid uplift during the later stages of the impact event.

Notes: The P–T paths for metamorphic complexes from the Precambrian shields and fold belts of different ages may result from advection, i.e. one-cycle convective processes in the lithosphere. This conclusion has been exemplified by the metamorphic evolution of several well-known complexes, for which an advective model can be successfully applied. Numerical simulations of the above processes in terms of Newtonian rheology by using a two-dimensional finite element program have been conducted.Two representative models for intracontinental gravitational ordering initiated presumably by mantle activity are considered: (i) a thermally activated multi-layered rhythmic sequence and (ii) huge rising diapiars causing circulation, in which crustal lithologies underwent high-P metamorphism (above 10–15 kbar) and subsequent ascent toward the Earth's surface.

Notes: The Waterman Metamorphic Complex of the central Mojave Desert was exposed as a consequence of early Miocene detachment-dominated extension. However, it has evidence consistent with a more extensive geological history that involves collision of a crustal fragment(s), tectonic thickening by overthrusting and two periods of extension. The metamorphic complex contains granitoid intrusives and felsic mylonitic gneisses as well as polymetamorphic rocks that include marble, calc-silicate, quartzite. mafic granulite, pyribolite, amphibolite, migmatite and biotite schist. The latter group of rocks was affected by an initial series of high-grade metamorphic events (M1 and M2) and a localized lower grade overprint (M3). The initial metamorphism (M1) can be separated into two stages along its high-grade P–T path: M1a, a granulite facies metamorphism at 800–850° C and 7.5–9 kbar and Mlb, an upper amphibolite facies overprint at 750–800° C and 10–12 kbar. M1a developed mineral assemblages and textures consistent with granulite facies conditions at a reduced activity of H2O and is associated with intense ductile deformation (D1) and minor local partial melting. M1b overprinted the granulite assemblages with a series of hydrous phases under conditions of increasing pressure and H2O activity and is accompanied by little or no deformation. M2 developed at lower pressures and temperatures (650–750° C, 4.5–5.5 kbar) and is distinguished by a second local overprint of hydrous phases that reflects an input of aqueous fluids probably associated with the intrusion of a series of granitic dykes and veins. Effects of M3 are confined to the Mitchel detachment zone, an anastomosing early Miocene detachment fault, and are characterized by local ductile/brittle deformation (D2) of the pre-existing high-grade rocks and granitoid intrusives and by the production of mylonites and mylonitic gneisses under greenschist facies conditions (300–350° C, 3–5 kbar). The initial overprint (M1a) represents metamorphism, devolatilization and minor partial melting of supracrustal rocks under granulite facies conditions as a consequence of tectonic and, possibly, magmatic thickening. The increasing pressure transition of M1a to M1b reflects a period of continued compressional tectonism, thrusting and influx of H2O, in part, locally related to crystallization of partial melts. The near isothermal decompression between M1b and M2 probably represents a pre-112-Ma extensional episode that may have been the result of a decompressional readjustment of a thickened crust. Following the initial extensional event, the metamorphic complex remained at depths of 10–17 km for at least 90 Ma until it was uplifted following Miocene extension. M3 develops locally in response to this second extensional period resulting from the early Miocene detachment faulting.

Notes: The High Himalayan Crystalline Sequence in north-central Nepal is a 15-km-thick pile of metasediments that is bound by the Main Central Thrust to the south and a normal fault to the north. The Langtang section through the metasediments shows an apparent inversion of metamorphic isograds with high-P, kyanite-grade rocks exposed beneath low-P, sillimanite-grade rocks. Textural evidence confirms that the observed inversion is a result of a polyphase metamorphic history and phase equilibria studies indicate that thermal decoupling has occurred within a mechanically coherent section of crust. Rocks now exposed at the base of the High Himalayan thrust sheet underwent Barrovian regional metamorphism (M1) prior to 34 Ma in the early stages of the Himalayan orogeny, recording metamorphic conditions of T= 710 ± 30° C, P= 9 ± 1 kbar. After the activation of the Main Central Thrust, which emplaced these metapelites southwards onto the lower grade Lesser Himalayan formations, the upper part of the thrust sheet was overprinted by a second heating event (M2), resulting in sillimanite-grade metamorphism and anatexis of metapelites at T= 760 ± 30° C, P= 5.8 ± 0.4 kbar between 17 and 20 Ma. Crustally derived, leucogranite magmas have been emplaced into low-grade Tethyan sediments on the hangingwall of the normal fault that bounds the northern limit of the metapelitic sequence.The cause of the selective heating of the upper section of the metasediments during M2 cannot be reconciled with either post-thrusting thermal relaxation or advection models. The cause of M2 remains problematical but it is suggested that heat focusing has occurred at the top of the High Himalayan Crystalline Sequence as a result of movement on the normal fault blanketing metapelites of high heat productivity with low-grade sediments of low thermal conductivity. This model implies that the normal fault was active before M2, consistent with decompression textures that formed during, or shortly after, sillimanite-grade metamorphism.

Notes: The two major Early to Middle Palaeozoic tectonic/metamorphic events in the northern Appalachians were the Taconian (Middle to Late Ordovician) in central to western areas and the Acadian (Late Silurian to early Middle Devonian) in eastern to west-central areas. This paper presents a model for the Acadian orogenic event which separates the Acadian metamorphic realm into eastern and western belts based on distinctively different styles. We propose that the Acadian metamorphism in the east was the delayed consequence of Taconian back-arc lithospheric modification. East of the Taconian island arc, thick accumulations of Late Ordovician and Silurian sediments, coupled with plutons rising along a magmatic arc, produced crustal thermal conditions appropriate for anomalously high-T, low-P metamorphism accompanied by major crustal anatexis. In this zone, upward melt migration was coupled with subsequent E-W crustal shortening (possibly due to outboard collision with the Avalon terrane) to produce mechanical conditions that favoured formation of fold and thrust nappes and resultant tectonic thickening to the west (and probably to the east as well).The basis for the distinction between the Eastern and Western Acadian events lies in the contrasting styles of metamorphism accompanying each. Evidence for contrasting metamorphic styles consists of (1) estimated metamorphic field gradients (MFGs) based on thermobarometric studies, and (2) petrological evidence for contrasting P–T trajectories. West of the Acadian metamorphic front, the Taconian zone has an MFG in which peak temperatures of 400-600° C were reached at pressures of about 4–6 kbar, with both P and T increasing to the east. Near its western edge, the Western Acadian metamorphic overprint has a similar MFG to the Taconian, and is mainly discriminated by 40Ar/39Ar dating and microtextural evidence. East of this narrow zone, the Western Acadian overprint is characterized by progressively higher temperatures (600–725° C) and pressures (6.5–10 kbar, or more) to the east, yielding an overall MFG that lies along, or slightly above, the kyanite–sillimanite boundary on a P–T diagram. There is little or no plutonism accompanying Western Acadian metamorphism.In contrast, thermobarometry in the Eastern Acadian, east of the Bronson Hill Belt, yields high-T, intermediate-P conditions for the highest grade rocks known in New England: T= 650–750° C, P= 4.5–6.5 kbar for granulite facies assemblages which apparently formed along an ‘anticlockwise’P–T path. The Bronson Hill Belt lies geographically between the Eastern and Western Acadian zones and shows transitional petrological behaviour: anomalously high temperatures at intermediate pressures, but a ‘clockwise’ path with decompression cooling.Radiometric dating indicates peak Taconian conditions may have been achieved as early as 475 Ma in the Taconian hinterland and as late as 445 Ma in the Taconian foreland (including the Taconic allochthons). Eastern Acadian magmatism may have started as early as 425 Ma, and most nappe-stage deformation and metamorphism in the Eastern Acadian zone appears to have ended by about 410 Ma. Tectonic thickening in the Western Acadian (including the western counterparts of the nappe-stage deformation documented in the Eastern Acadian) must pre-date attainment of peak metamorphic conditions dated at 395–385 Ma. Dome-stage deformation clearly post-dates peak metamorphism and deforms metamorphic isograds. The end of Western Acadian deformation is well constrained by 370-375 Ma radiometric ages of late pegmatites and granitoids which cross-cut all structures.

Notes: A suite of migmatites in uppermost amphibolite facies schists of the Koettlitz Group exposed in the Taylor Valley, Antarctica, provides direct evidence of the behaviour of partially molten rock during syn-anatectic deformation. The geometry of the migmatites is directly related to their position relative to the hinge of a kilometre-scale antiform. Migmatitic rocks on the fold limbs are characterized by extensional shears and fractures, filled with leucosome material, that intersect the pervasive foliation and millimetre-thick stromatic leucosomes. Vein- and dyke-like leucosomes become more common and thicker from the limb to the hinge region of the antiform. Rocks characterized by high leucosome-to-rock ratios near the antiform hinge are xenolithic in appearance. Major parasitic folds within the hinge contain leucogranite ‘microplutons’ up to 50 m across beneath refractory ‘cap-rock’ layers.Angular boudinage structures in schists surrounded by leucosomes indicate a relatively low yield strength in the leucosome, which is compatible with a molten rather than solid leucosome. Leucogranite-bearing extensional shears and fractures indicate that repeated extensional fracturing and shearing promoted by high fluid (melt) pressure is an important mechanism of melt segregation. Dilation in the hinges of developing folds aids the migration of melt into fold hinges and the development of 10–50-m-wide ‘microplutons’ of xenolith-rich leucogranite.Lack of vapour-absent melting and consequent low melt-to-rock ratios allowed the Koettlitz Group to maintain its structural coherency on a kilometre scale. Consequently, leucosome ‘microplutons’ did not exceed 50 m in width, and therefore observed leucosomes have not contributed to the development of adjacent plutonic-scale granitoids.

Notes: Systematic mapping of a transect along the well-exposed shores of Georgian Bay, Ontario, combined with the preliminary results of structural analysis, geochronology and metamorphic petrology, places some constraints on the geological setting of high-grade metamorphism in this part of the Central Gneiss Belt. Correlations within and between map units (gneiss associations) have allowed us to recognize five tectonic units that differ in various aspects of their lithology, metamorphic and plutonic history, and structural style. The lowest unit, which forms the footwall to a regional decollement, locally preserves relic pre-Grenvillian granulite facies assemblages reworked under amphibolite facies conditions during the Grenvillian orogeny. Tectonic units above the decollement apparently lack the early granulite facies metamorphism; out-of-sequence thrusting in the south produced a duplex-like structure. Two distinct stages of Grenvillian metamorphism are apparent. The earlier stage (c. 1160–1120 Ma) produced granulite facies assemblages in the Parry Sound domain and upper amphibolite facies assemblages in the Parry Island thrust sheet. The later stage (c. 1040–1020 Ma) involved widespread, dominantly upper amphibolite facies metamorphism within and beneath the duplex. Deformation and metamorphism recently reported from south and east of the Parry Sound domain at c. 1100–1040 Ma have not yet been documented along the Georgian Bay transect. The data suggest that early convergence was followed by a period of crustal thickening in the orogenic core south-east of the transect area, with further advance to the north-west during and after the waning stages of this deformation.

Notes: The Main Zone of the Hidaka metamorphic belt is an imbricate stack of crustal material derived from an island arc in which a sequence of units with increasing metamorphic grade from low to high structural levels is exposed. The basal part of the metamorphic sequence underwent granulite facies metamorphism with peak P–T conditions of 7kbar, 870°C. In this zone pelitic granulite includes leucosomes which consist mainly of orthopyroxene-plagioclase-quartz.To test whether the leucosome was derived by partial melting of the surrounding pelite, melting experiments of the pelitic granulite were carried out for water-saturated and dry systems at 7 kbar and 850°C. The chemical composition of the leucosome produced during these runs shows a peraluminous S-type tonalitic affinity and is located very close to the tie-line between the average melts produced in water-saturated systems and the average composition of the residual orthopyroxene + plagioclase. This therefore suggests that the lecosome in pelitic granulite was formed by incipient anatexis at close to the highest P–T condition of the Main Zone.The age of the crustal anatexis is determined by the Rb-Sr whole rock isochron method for garnet-cordierite-biotite gneiss (host rock), garnet-orthopyroxene-cordierite gneiss (restite) and S-type tonalite (melt). This gives an age of 56.0 Ma with an initial 87Sr/86Sr ratio of 0.705711. The S-type tonalite magmas that form large intrusive masses in the Main Zone were probably generated by crustal anatexis in deeper parts of the crust at the same time (late Palaeocene).

Notes: Caledonian eclogite facies shear zones developed from Grenvillian garnet granulite facies anorthosites and gabbros in the Bergen Arcs of western Norway allow direct investigation of the relations between macroscopic structures and crystallographic preferred orientation (CPO) in lower continental crust. Field relations on the island of Holsnøy show that the eclogites formed locally from granulite facies rocks by progressive development of: (1) eclogite adjacent to fractures; (2) eclogite in discrete shear zones (〉 2 m thick); (3) eclogite breccia consisting of 〉80% well-foliated eclogite that wraps around rotated granulite blocks; and (4) anastomosing, subparallel, eclogite facies shear zones 30–100 m thick continuous over distances 〉 1 km within the granulite terrane. These shear zones deformed under eclogite facies conditions at an estimated temperature of 670 ± 50°C and a minimum pressure of 1460 MPa, which corresponds to depths of 〉55 km in the continental crust. Detailed investigation of the major shear zones shows the development of a strong foliation defined by the shape preferred orientation of omphacite and by alternating segregations of omphacite/garnet-rich and kyanite/zoisite-rich layers. A consistent lineation throughout the shear zones is defined by elongate aggregates of garnet and omphacite. The CPO of omphacite, determined from five-axis universal stage measurements, shows a strong b-axis maximum normal to foliation, and a c-axis girdle within the foliation plane with weak maxima parallel to the lineation direction. These patterns are consistent with deformation of omphacite by slip parallel to [001] and suggest glide along (010). The lineation and CPO data reveal a consistent sense of shear zone movement, although the displacement was small. Localized faulting of high-grade rocks accompanied by fluid infiltration can be an important mode of failure in the lower continental crust. Field relations show that granulite facies rocks can exist in a metastable state under eclogite facies conditions and imply that the lower crust can host differing metamorphic facies at the same depth. Deformation of granulite and partial conversion to eclogite, such as is exposed on Holsnøy Island, may be an orogenic-scale process in the lowermost crust of collisional orogens.

Notes: Mineral composition and quantitative thermobarometric studies indicate that the Teslin-Taylor Mountain and Nisutlin terranes within the Teslin suture zone (TSZ), Yukon, record widespread high-P/T metamorphic conditions consistent with subduction zone dynamothermal metamorphism. The highest P–T conditions (575–750° C and 9–17 kbar) are preserved in tectonites formed during normal dip-slip ductile shear. Dextral strike-slip tectonites record lower P–T conditions (400–550° C and 5–8 kbar), and tectonites which show reverse shear have peak temperatures of c. 420° C and a minimum peak pressure of 3 kbar. Dynamothermal metamorphism took place in a west-dipping B-type subduction zone outboard of western North America in Permo-Triassic time. TSZ tectonites were underplated against the hangingwall plate of the subduction zone. Following subduction of the ocean basin which separated North America from the hangingwall plate, TSZ tectonites were overthrust eastward as a coherent structural package as a result of A-type subduction of Cassiar strata in early Jurassic time.(Par)autochthonous Cassiar tectonites, which comprised the leading edge of the western North American margin, record prograde moderate-P, high-T metamorphism (550–750° C and 7–13 kbar) synchronous with top-to-the-east ductile shear. Metamorphism occurred as a result of subduction of the North American margin into the TSZ subduction zone in early Jurassic time. Following metamorphism Cassiar tectonites cooled slowly from 500 to 300° C during the period middle Jurassic to middle Cretaceous.TSZ and Cassiar tectonites were deformed during changing P–T conditions. Data from each of these tectonite packages indicate that grain-scale strain partitioning may have allowed local recrystallization of individual minerals by the addition of mechanical energy. The composition of the new grains reflects the P–T conditions under which that particular grain was deformed.

Notes: The Al–Mg-rich granulites from the In Ouzzal craton, Algeria, show a great diversity of mineral reactions which correspond to continuous equilibria as predicted by phase relationships in the FeO–MgO–Al2O3–SiO2 system. The sequence of mineral reactions can be subdivided into three distinct stages: (1) a high-P stage characterized by the growth of coarse mineral assemblages involving sapphirine and the disappearance of early corundum and spinel-bearing assemblages; (2) a high-T stage characterized by the development of Sa–Qz-bearing assemblages; and (3) a later stage, in which garnet-bearing assemblages are replaced by more or less fine symplectites involving cordierite.During the course of early mineral reactions, the distribution coefficient, Kd, between the various ferromagnesian phases decreased significantly whereas Al2O3 in pyroxene increased concomitantly. These observations, when combined with topological constraints, clearly indicate that the high-P stage 1 was accompanied by a significant rise in temperature (estimated at 150 ± 50° C) under near isobaric conditions, in agreement with the reaction textures. By stage 2, pressure and temperature were extreme as evidenced by the low Kd value between orthopyroxene and garnet (Kd= 2.06–1.99), the high alumina content in pyroxene (up to 11.8%) and the high magnesium content in garnet [100 Mg/(Mg + Fe) = 60.6]. Mineral thermometry based on Fe–Mg exchange between garnet and pyroxene and on Al-solubility in pyroxene gives temperatures close to 970 ± 70° C at 10 ± 1.5 kbar. These results are in agreement with the development of Sa–Qz assemblages on a local scale.Late mineral reactions have been produced during a decompression stage from about 9 to 6 kbar. Except for local re-equilibration of Mg and Fe at grain boundaries, there is no evidence for further reactions below 700° C.We interpreted the whole set of mineral reactions as due to changes in pressure and temperature during a tectonic episode located at c. 2 Ga. Because of the lack of evidence for further uplift after the thermal relaxation which occurred at c. 6 kbar, it is possible however that the exhumation of this granulitic terrane occurred in a later tectonic event unrelated to its formation.

Notes: Investigation of microstructural relationships in major movement zones in metamorphic rocks, where the sense of displacement is known from regional geological relationships, indicates numerous problems with current concepts of shear-sense criteria and their application. The direction of apparent shearing commonly conflicts from one criterion to another (e.g. from the symmetry of quartz c-axis orientation diagrams to the asymmetry of extensional crenulation cleavages). This implies that interpretations of shear sense along foliations from some mesoscale and microscale criteria have been erroneous.A new approach to interpreting shear sense, involving the use of strain fields, resolves conflicts in mesoscopic and microscopic criteria and provides a method for determining coherent shear-sense histories extending back before the last shearing event for ‘any foliated metamorphic rock’. It also provides a powerful tool for determining the structural/metamorphic path that a rock has followed within an orogen. For determination of the shear sense on the last foliation developed in a rock, this approach uses geometries developed around competent heterogeneities such as quartz pebbles, pegmatite pods, veins, porphyroclasts, porphyroblasts and breccia clasts. A shear-sense history is derived by applying this approach to earlier foliations preserved within the heterogeneities and their strain shadows.

Notes: Sapphirine occurs in a 3-5 m wide zone between amphibole-lherzolite and garnetiferous metagabbro at Finero in the Ivrea Zone, NW Italian Alps. Layers consisting of plag + hb + sa + cpx + opx + sp + gt are interbanded with spinel pyroxenites, which may contain sapphirine replacing spinel. All minerals are very magnesian, with XMg between 0.78 and 0.92. Bulk rock analyses suggest that precursors to the sapphirine-bearing rocks were igneous cumulates of plagioclase + olivine + hornblende + spinel. Up to 16wt% CaO does not inhibit sapphirine formation and it is the unusually Mg-rich nature of the host rocks which allows sapphirine development. The early igneous assemblage was replaced by one of cpx + sa + hb +± plag at a pressure of 9 ± 1 kbar and temperatures of 900 ± 50°C. Subsequent rapid uplift caused the instability of gt, gt + hb, hb and sa + cpx to form opx + plag ± sp ± sa symplectites.

Notes: The Gran Paradiso basement complex of the French and Italian Alps is composed of metasediments, termed the gneiss minuti, and metabasic rocks, both of which are intruded by a late Hercynian granite. The Bonneval gneiss, which crops out at the western edge of the complex, is composed of highly deformed metasediments, volcanics and volcaniclastic rocks. Eclogites, now highly altered, occur in the metabasic rocks. Kyanite and blue-green amphibole are locally present in the gneiss minuti and aegirine plus riebeckite occur in the Bonneval gneiss. A moderately high pressure - low temperature metamorphic event of probable Alpine age occurred in the basement complex. This metamorphic event differs from that in the overlying Sesia unit and ophiolites of the Schistes lustrés nappe in being at lower pressures (below the ab = jd100+ qz transition) and post-dating the major (D2A) deformation. The origin of the metamorphism is discussed and interpreted as a probable consequence of the overlying nappe pile which was emplaced during the D2A event. Subsequent greenschist facies metamorphism in the basement complex is a consequence of thermal relaxation during uplift.

Notes: Abstract. A method for the quantitative analysis of the spatial relations of minerals is described. Dispersed distributions are formed by annealing and destroyed in post-tectonic migmatization. Aggregate distributions characterize solid-state differentiation, whereas leucosomes formed in systems of high fluid:rock ratio (in the examples studied, anatectic melts) show random distributions.Quantitative textural analysis can be used to indicate whether migmatization was post-tectonic or earlier, though caution is necessary if post-migmatite cooling is slow or if there is some minor deformation. More importantly, it can be used to discriminate melt-present from melt-absent leucosomes; this is exemplified by a suite of metamorphic and anatectic migmatites from the Scottish Caledonides.The textural evolution of anatexites with increasing melt percentage is traced. Initial feldspar porphyroblastesis occurs by Ostwald ripening via grain boundary melts; subsequently ophthalmites develop with fabrics and chemistry inherited from the palaeosome. At greater than 30% melt these inherited fabrics are wholly destroyed. Deformation prompts segregation into melanosome and leucosome; resultant leucosomes contain no inherited crystals. The scale of anatectic systems is fixed at the point at which segregation begins; ophthalmites provide evidence for melt and crystal transfer beyond original palaeosome boundaries. In contrast, metamorphic migmatites are necessarily small-scale systems because of diffusive constraints, and melanosomes are invariably produced.

Notes: The oligoclase-biotite zone of the Bessi area, central Shikoku is characterized by sodic plagioclase (XCa= 0.10–0.28)-bearing assemblages in pelitic schists, and represents the highest-grade zone of the Sanbagawa metamorphic terrain. Mineral assemblages in pelitic schists of this zone, all with quartz, sodic plagioclase, muscovite and clinozoisite (or zoisite), are garnet + biotite + chlorite + paragonite, garnet + biotite + hornblende + chlorite, and partial assemblages of these two types. Correlations between mineral compositions, mineral assemblages and mineral stability data assuming PH2O = Psolid suggests that metamorphic conditions of this zone are about 610 ± 25°C and 10 ± 1 kbar.Based upon a comparative study of mineralogy and chemistry of pelitic schists in the oligoclase-biotite zone of the Sanbagawa terrain with those in the New Caledonia omphacite zone as an example of a typical high-pressure type of metamorphic belt and with those in a generalized‘upper staurolite zone’as an example of a medium-pressure type of metamorphic belt, progressive assemblages within these three zones can be related by reactions such as:

Notes: An assemblage consisting of corundum, sapphirine, spinel, cordierite, garnet, biotite and bronzite is described from the Messina area of the Limpopo Mobile Belt, and consideration given to its petrogenesis. Various geothermometers and geobarometers have been applied in an attempt to determine the temperatures and pressures of metamorphism.A former coexistence of garnet and corundum is suggested to have developed during the earliest high pressure phase of the metamorphism, where temperatures exceeded 800°C and pressures as high as 10kbar may have been experienced. Subsequently, continuous retrograding reactions from medium pressure granulite facies at about 800°C and 8kbar towards amphibolite facies generated spinel, cordierite, sapphirine and possibly also bronzite. The most notable reaction was probably of the form: garnet + corundum = cordierite + sapphirine + spinel.

Notes: A review of currently available information relevant to the Basal Gneiss Complex (BGC) of Western South Norway, combined with the authors’own observations, leads to the following conclusions.1. Most of the BGC consists of Proterozoic crystalline rocks and probably subordinate Lower Palaeozoic cover.2. The last major deformation of these rocks was during the Caledonian orogeny and involved large-scale thrusting, recumbent folding and doming. The structural development of the BGC is closely tied in with that of the Caledonian allochthon.3. The whole eclogite-bearing part of the BGC has suffered a high pressure metamorphism with conditions of between 550°C, 12.5 kbar (Sunnfjord) and about 750°C, 20 kbar (Møre og Romsdal) at the metamorphic climax.4. This metamorphism was of Caledonian age, probably rather early in the Caledonian tectonic history of the BGC and is considered to have been a rather transient event.By setting these conclusions in a framework provided by geophysical evidence for the deep structure of the crust in southern Norway we have constructed a geotectonic model to explain the recorded metamorphic history of the BGC. It is suggested that considerable crustal thickening was caused by imbrication of the Baltic plate margin during continental collision with the Greenland plate. This resulted in high pressure metamorphism in the resulting nappe stack. Progradation of the suture caused underthrusting of the Baltic foreland below the eclogite-bearing terrain causing it to emerge at the Earth's surface, aided by tectonic stripping and erosion.Application of isostacy equations to the model shows that eclogites can be formed by in-situ metamorphism in crustal rocks and reappear at the land surface above a normal thickness of crust in a single orogenic episode of approximately 65-70 Ma duration.

Notes: Graphitization and coarsening of organic material in carbonate-bearing metasedimentary rocks is accompanied by carbon isotope exchange which is the basis of a refractory, pressure-independent geothermometer. Comparison of observed isotopic fractionations between calcite and graphite (δ13CCal–Gr) with independent petrological thermometers provides the following empirical calibration over the range 400–800°C: δ13CCal–Gr= 5.81 times 106×T–2(K) - 2.61. This system has its greatest potential in marbles where calcite + graphite is a common assemblage and other geothermometers are often unavailable. The temperature dependency of this empirical calibration differs from theoretical calibrations; reasons for this are unclear but the new empirical calibration yields temperature estimates in better agreement with independent thermometry from several terranes and is preferred for geological applications.Both calcite-graphite isotopic thermometry and calcite-dolomite solvus thermometry are applied to marble adjacent to the Tudor gabbro in the Grenville Province of Ontario, Canada. The marble has undergone two metamorphic episodes, early contact metamorphism and later regional metamorphism. Values of δ13CCal–Gr decrease regularly from c. 8‰ in samples over 2 km from the pluton to values of 3–4‰ within 200 m of the contact. These samples appear to preserve fractionations from the early thermal aureole with the empirical geothermometer, and indicate temperatures of 450–500° C away from the intrusion and 700–750°C near the gabbro. This thermal profile around the gabbro is consistent with conductive heat flow models. In contrast, the distribution of Mg between calcite and dolomite has been completely reset during later regional metamorphism and yields uniform temperatures of c. 500°C, even at the contact.Graphite textures are important for interpreting the results of the calcite–graphite thermometer. Coarsening of graphite approaching the Tudor gabbro correlates with the decrease in isotopic fractionations and provides textural evidence that graphite crystallization took place at the time of intrusion. In contrast to isotopic exchange during prograde metamorphism, which is facilitated by graphitization, retrogressive carbon isotopic exchange appears to require recrystallization of graphite which is sluggish and easily recognized texturally. Resistance of the calcite–graphite system to resetting permits thermometry in polymetamorphic settings to see through later events that have disturbed other systems.

Notes: In order to illustrate different applications of the amphibole-albite-chlorite-epidote-quartz geothermobarometer, pressure-temperature-time (P–T–t) ± space (P–T–t–s) ± deformation (P–T–t–d) paths have been established from literature data. They are discussed as a function of the chemical, equilibrium and microstructural data available in each case, and compared with the conclusions already established by other methods. It is clear that it is necessary to know the relative chronology of the events (directions of zoning of minerals in successive microstructural positions) to establish precise P–T paths; this enables reconstruction of complex geodynamic histories. From this point of view, it is necessary to analyse the maximum possible number of minerals in a few well-chosen metabasic rocks showing different generations of blastesis. The rocks should belong to different tectonic units to obtain the best overall picture of a metamorphic complex.

Notes: In a number of recent papers, the theory has been postulated that porphyroblasts as a rule do not rotate with respect to geographical coordinates, and can be used to determine the original orientation of older foliations. Complex inclusion patterns in spiral garnets have even been used to advocate a new model of orogenesis, involving several alternating phases of horizontal shortening and extension. Critical assessment of the assumptions and data used to support the theory of irrotational porphyroblasts reveals numerous flaws. Millipede structures, used as proof for flow partitioning, can also form by other flow geometries. Evidence quoted to support irrotational behaviour of porphyroblasts is unsound. Porphyroblasts do occur in sets with a preferred orientation of the internal foliation trace, but these cannot be shown to represent original orientations. Microstructures which resemble truncation planes in spiral garnets are used as evidence that these structures developed by several phases of deformation and as proof for periodic extension and horizontal shortening in orogenesis. They can, however, also be explained by intermittent growth of a rotating porphyroblast during a single phase of deformation. Finally, porphyroblast sets in which orientation is a function of aspect ratio indicate that porphyroblast rotation with respect to kinematic axes does occur in at least some situations.

Notes: In the Hazeldene area, situated in the Mount Isa Inlier, Queensland, the metamorphic grade changes from chlorite zone, through biotite and cordierite zones, to sillimanite/K-feldspar zone.Microstructural studies of rocks near the sillimanite isograd demonstrate that cordierite grew early during the development of a steep foliation (S2), was replaced by biotite, andalusite and sillimanite at the metamorphic peak late in S2, and in turn by kyanite + chlorite adjacent to localized small post-D2 shear zones. Although the anticlockwise P–T–t path is well defined, the precise P–T conditions are uncertain because of problems with experimental and thermodynamic data. The best estimate for the metamorphic peak for rocks close to the sillimanite isograd is around 600° C at 4 kbar.The metamorphism has been dated at 1544 Ma, and was synchronous with a major crustal shortening event. Because proposed extensional events occurred more than 60 Ma earlier, their contribution to the peak metamorphic thermal perturbation would have been insignificant. The syn-metamorphic Mica Creek Pegmatites, the abundance of high heat-producing elements in the nearby pre-D2 Sybella Granite, and advective heat by fluids which caused considerable metasomatism in the Hazeldene area, may have each contributed to the thermal budget. However, the metamorphic thermal gradient may be 80°C km-1 or higher, strongly suggesting a local magmatic control. As none are known in the area, such syn-metamorphic plutons would have to lie beneath the exposed high-grade rocks.

Notes: Charnockitic alteration (arrested orthopyroxene formation in biotite- and amphibole-bearing rocks) occurs in high-grade terranes of all ages. Three criteria are used to show that this alteration was produced in many locations by a migrating fluid phase: (i) diffuseness of the alteration—the alteration zones are often quite unlike discrete migmatitic veins; (ii) relation to deformation—most occurrences show alteration closely associated with warping of foliation or dilation cracks; (iii) open-system alteration—whilst some occurrences represent nearly isochemical alteration, slight changes in bulk composition, often loss of mafic constituents and gain of Na and Si, are evident in detailed mass-balance analysis. Y and sometimes Rb are characteristically depleted. Partial melting sometimes accompanied volatile infiltration, as evidenced by more discrete veins and euhedral orthopyroxene. It is quite unlikely, however, that open-system alteration was produced by escape of viscous quartzo-feldspathic melts. Pervasive migration of low-T lamprophyric (mafic–alkaline, CO2-charged) interstitial liquids is a possibility by virtue of their extreme fluidity, but CO2 infiltration was needed to generate these liquids. Vapour-deficient dehydration melting is another feasible mechanism of orthopyroxene formation which may have operated in conjunction with CO2 infiltration.Characteristic development of charnockitic alteration in some prograde amphibolite to granulite facies transitions, as in the Dharwar Craton of South India, suggests that the alteration is a fundamental feature of the granulite facies metamorphism, implying active and causal participation of migrating fluids. In other high-grade terranes like the Adirondack Mountains of New York, this kind of alteration is rare, and fluid action does not seem to have been important in the metamorphism.A vapour phase participating in charnockitic metamorphism was necessarily one of relatively low H2O, therefore presumably rich in CO2. Consideration of possible large CO2 sources leads to the conclusion that emanations from volatile-rich basalts emplaced in the lower crust are the most probable source of charnockitizing fluids. The ultimate source would therefore be enriched subcontinental lithosphere or asthenosphere. The Rb-depleted pyroxene gneiss (charnockitic) terranes may be characteristic of zones of large-scale transcurrent or oblique-motion faults which tap such great depths.

Notes: Quartz veins are developed in a wide range of metasediment types in the upper amphibolite facies rocks of Connemara, and attest to considerable migration of silica. Contrary to common assumptions, there is clear evidence that these veins do not primarily result from movement of fluid to regions of lower P–T down the regional geothermal gradient. Under amphibolite facies conditions, a dilute chloride fluid moving down temperature has the potential to alter 60g of plagioclase to muscovite for each gram of vein quartz precipitated, while cooling over the temperature interval from 650 to 500° C. The absence of significant metasomatic effects in the vein walls effectively precludes a simple origin from such through-flowing, externally derived fluids. The oxygen isotopic composition of matrix quartz shows considerable differences between different rock types (quartzite, pelite and marble), with a range of δ18OSMOW from c.+ 11.5% (quartzite) to + 18.5% (marble). In each rock type, vein quartz compositions closely match those of the matrix quartz. These results demonstrate the importance of local segregation processes in the formation of veins, and suggest that fluid convection cells were not developed during metamorphism on a scale larger than the individual sedimentary formations, if at all.Both oxygen isotope data and the absence of metasomatism indicate that veins form primarily by segregation of quartz from the host lithologies, with only a relatively minor component of through flow of externally derived fluid. Veins are clearly not the major pathways of metamorphic dewatering.It is proposed that abundant veins in the predominantly pelitic Ballynakill Formation formed during peak metamorphic D3 folding because the formation was embrittled by high fluid pressures but was capped by impermeable marble. Hence the pelitic formation fractured repeatedly and the pore fluid drained through the fractures to form veins, while irreversible loss through the rest of the succession was a much less important process.In the central mountains of Connemara, rather pure, unreactive quartzites are cut by widely spaced, laterally extensive quartz veins that are axial planar to D3 folds. These veins may mark pathways whereby metamorphic fluid made its way through the massive impermeable quartzite from lower parts of the nappe pile, but here too, oxygen isotope data indicate considerable segregation of locally derived quartz, reflecting the importance of pumping of fluid between wail rocks and fractures relative to the component of through flow.

Notes: Geothermometry and geobarometry of 10 garnet–oligoclase zone schists in the Franz Josef–Fox Glacier area, Southern Alps, New Zealand, give temperatures ranging from 415 to 625°C and pressures from 5.2 to 9.2 kbar, indicating a T–P array of about 50°C/kbar and inferred peak temperature conditions over a c. 15-km-thick section at depths between c. 20 and 34 km. The present-day distribution of the schist samples implies that only about one-third of the original crustal section is now exposed.The garnet–oligoclase zone schists represent the deeper part of a metamorphosed and deformed accretionary complex that was associated with late Palaeozoic–early Mesozoic subduction along the Gondwana continental margin. Partial uplift (c. 0.2 m/Ma) and erosion of the complex during Jurassic–Cretaceous times (Rangitata uplift) was synchronous with D2 deformation and recrystallization, as recorded by the P–T array. Cenozoic (Kaikoura) uplift and exhumation of the schist since c. 30 Ma to form the Southern Alps was associated with oblique-slip movement on the Alpine Fault. The present-day position and steep eastward dip of isograds and D2 structures suggest considerable clockwise rotation during uplift associated with ductile attenuation and tectonic thinning by over two-thirds of the original schist sequence, largely due to simple shear along schistosity planes. As the schist generally shows only incipient greenschist facies retrograde recrystallization, an apparently complete (although contracted) prograde mineral sequence has been preserved by rapid uplift (〉5 km/Ma) of hot rock and the effects of limited shear heating near the Alpine Fault.

Notes: The Smartville Complex is a late Jurassic, rifted volcanic arc in the northern Sierra Nevada, California. Near Auburn, California, it consists of a lower volcanic unit, dominated by basaltic flows, and an upper volcanic unit of andesitic volcaniclastic rocks, both of which have been intruded by dykes and irregular bodies of diabase. These rocks contain relict igneous minerals, and the metamorphic minerals albite, chlorite, quartz, pumpellyite, prehnite, epidote, amphibole, titanite, garnet, biotite, K-feldspar, white mica, calcite, and sulphide and oxide minerals.Prehnite–pumpellyite (PrP), prehnite–actinolite (PrA), and greenschist (GS) zones have been identified. The pumpellyite-out isograd separates the PrP and PrA zones, and the prehnite-out isograd separates the PrA and GS zones. The minerals Ab + Qtz + Mt + Tn are common to most assemblages in all three zones. The MgO/(MgO + FeO) ratio of the effective bulk composition has an important and systematic effect on the observed mineral assemblages in the PrP zone. Prehnite-bearing assemblages contain the additional minerals, Pmp + Amp + Ep + Chl in MgO-rich rocks, and either Pmp + Ep + Chl or Amp + Ep + Chl in less magnesian rocks. Subcalcic to calcic amphibole is common in the PrP zone. The mineral assemblage Prh + Act + Ep + Chl, without Pmp, characterizes the PrA zone, and the mineral assemblage Act + Ep + Chl, without Prh or Pmp, characterizes the GS zone. The disappearance of pumpellyite and prehnite occurred by continuous reactions.The sequence of mineral assemblages was produced by burial metamorphism at P–T conditions of 300° 50°C at approximately 2.5 ± 0.5 kbar. During metamorphism, the composition of the fluid phase was nearly 100% H2O and the oxygen fugacity was between the hematite–magnetite and quartz–fayalite–magnetite buffers.

Notes: Garnet-bearing mineral assemblages are commonly observed in pelitic schists regionally metamorphosed to upper greenschist and amphibolite facies conditions. Modelling of thermodynamic data for minerals in the system Na2O–K2O–FeO–MgO–Al2O3–SiO2–H2O, however, predicts that garnet should be observed only in rocks of a narrow range of very high Fe/Mg bulk compositions. Traditionally, the nearly ubiquitous presence of garnet in medium- to high-grade pelitic schists is attributed qualitatively to the stabilizing effect of MnO, based on the observed strong partitioning of MnO into garnet relative to other minerals. In order to quantify the dependence of garnet stability on whole-rock MnO content, we have calculated mineral stabilities for pelitic rocks in the system MnO–Na2O–K2O–FeO–MgO–Al2O3–SiO2–H2O for a moderate range of MnO contents from a set of non-linear equations that specify mass balance and chemical equilibrium among minerals and fluid. The model pelitic system includes quartz, muscovite. albite, pyrophyllite, chlorite, chloritoid, biotite, garnet, staurolite, cordierite, andalusite, kyanite. sillimanite, K-feldspar and H2O fluid. In the MnO-free system, garnet is restricted to high Fe/Mg bulk compositions, and commonly observed mineral assemblages such as garnet–chlorite and garnet–kyanite are not predicted at any pressure and temperature. In bulk compositions with XMn= Mn/(Fe + Mg + Mn) 〉 0.01, however, the predicted garnet-bearing mineral assemblages are the same as the sequence of prograde mineral assemblages typically observed in regional metamorphic terranes. Temperatures predicted for the first appearance of garnet in model pelitic schist are also strongly dependent on whole-rock MnO content. The small MnO contents of normal pelitic schists (XMn= 0.01–0.04) are both sufficient and necessary to account for the observed stability of garnet.

Notes: The Velay dome (French Massif Central) offers a quasi-continuous section across an anatectic domain comprising low- to high-grade schists, gneisses and granites. Two main tectonometamorphic events, and their related generation of granitic material, were recognized in addition to a major Barrrovian tangential event (D2) attributed to intracontinental collision tectonics: (i) a medium- to low-P, high-T event (D3) which gave rise to migmatites and syntectonic monzonitic granites and granodiorites, and (ii) a widespread melting event (D4) which led to the generation of migmatities, the Velay granite and post-anatectic granites.Thermobarometry on samples collected from both the metamorphic envelope and the granitic core distinguishes two distinct geotherms: (i) a first, associated with the D3 event, characterized by P 〉 5 kbar, T≤ 750° C and water-present melting (biotite remains stable) which led to large-scale migmatization but minor amount of granites; (ii) a second, associated with the D4 event and characterized by vapour-absent melting (P= 4–5 kbar, T= 760–850° C) which gave rise to the Velay granites and late-migmatitic granites. The temperature increase during the D4 event is attributed to the intrusion of hot mafic magmas within the crust.The time-integrated features of the different granitic rocks in the Velay dome can be directly related to aH2O in the source region and illustrate the progressive dehydration of a middle to lower crustal segment over 60 Ma.

Notes: Metabasaltic rocks in the Klamath Mountains of California with ‘komatiitic’ major element concentrations were investigated in order to elucidate the origin of the magnesian signature. Trace-element concentrations preserve relict igneous trends and suggest that the rocks are not komatitic basalts, but immature arc rocks and within-plate alkalic lavas. Correlation of ‘excess’ MgO with the volume per cent hornblende (±clinopyroxene) suggests that the presence of cumulus phases contributes to the MgO-rich compositions. Early submarine alteration produced regional δ18O values of +10±1.5%° and shifts in Al2O3, Na2O, and K2O concentrations. Regional metamorphic grade in the study area varies from biotite-zone greenschist facies (350–550°C, c. 3 kbar) southward to prehnite–actinolite facies (200–400°C, ≤3 kbar), but little isotopic or elemental change occurred during the regional recrystallization. The greenschist facies assemblage is actinolitic hornblende + phengite + epidote + sodic plagioclase + microcline + chlorite + titanite + hematite + quartz in Ti-poor metabasaltic rocks; in addition to these phases biotite is present in Ti-rich analogues. Lower grade greenstones contain prehnite and more nearly stoichiometric actinolite. The moderate to low pressures of regional metamorphism are compatible with P–T conditions in a magmatic arc. Later contact metamorphism at 2–2.9±0.5 kbar and at peak temperatures approaching 600° C around the English Peak and Russian Peak granodiorites produced 3–4–km-wide aureoles typified by gradual, systematic increases in the pargasite content of amphibole, muscovite content of potassic white mica, and anorthite content of plagioclase compositions. Metasomatism during contact metamorphism produced further increases in bulk-rock δ18OSMOW of as much as +6%°. Thus, the unusually MgO-rich nature of the Sawyers Bar rocks may be attributed at least partly to metasomatism and the presence of magnesian cumulus phases.

Notes: Detailed geochronological, structural and petrological studies reveal that the geological evolution of the Field Islands area, East Antarctica, was substantially similar to that of the adjacent Archaean Napier Complex, though with notable differences in late and post Archaean times. These differences reflect the area's proximity to the Proterozoic Rayner Complex and consequent vulnerability to tectonic process involved in the formation of the latter. Distinctive structural features of the Field Islands are (1) consistent development of a discordant, pervasive S3 axial-plane foliation; (2) re-orientation of S3 axial planes to approximate to the subsequent E-W tectonic trend of the nearby Rayner Complex; (3) selective retrogression by a post-D3 static thermal overprint; and (4) relatively common development of retrogressive, E-W-trending, mylonitic shear zones.Peak metamorphic conditions in excess of 800°C at 900 ± 100 M Pa (9 kbar) were attained at one locality following, but probably close to the time of D2 folding. D3 took place in late Archaean times when metamorphic temperatures were about 650°C and pressures were about 600 MPa (6 kbar). Later, temperatures of 600 ± 50°C and pressures of 700 MPa (7kbar) were attained in an amphibolite-facies event, presumably associated with the widespread granulite to amphibolite-facies metamorphism and intense deformation involved in the formation of the Rayner Complex at about 1100 Ma. The area was subsequently subjected to near-isothermal uplift.Rb-Sr isotopic data indicate that the pervasive D3 fabric developed at about 2400–2500 Ma, and this age can be further refined to 2456+8-5 Ma by concordant zircon analyses from a syn-D3 pegmatite. All zircons were affected by only minor (〈7–10%) Pb loss and/or new zircon growth during the Rayner event at about 1100Ma. Thus the 450–850 μg/gU concentrations of these zircons were too low to cause sufficient lattice damage over the 1350 Ma (from 2450 Ma) for excessive Pb to be lost during the 1100 Ma event. The emplacement of pegmatite at 522 ± 10 Ma substantially changed the Rb-Sr systematics of the only analysed rock that developed a penetrative fabric during the 1100 Ma event. Monazite in this pegmatite contains an inherited Pb component, which probably resides in small opaque inclusions.A good correlation is found between Rb-Sr total-rock ages and rock fabric. U-Pb zircon intercepts with concordia also mostly correspond to known events. However, in one example a near perfect alignment of zircon analyses, probably developed by mixing of unrelated components, produced concordia intercepts that appear to have no direct geochronological significance.

Notes: Because many durable goods industries are also industries with significant innovative activity, we analyze the relationship between an oligopolistic firm's choice of product durability and cost-reducing innovation in rental and sales markets. We demonstrate the firm's durability may be greater than, equal to, or less than a social planner's, depending upon innovation's impact on the marginal cost of durability. We also show that the firm's innovation level can be maximized for moderate levels of concentration if the output is durable. This provides theoretical support for the empirical observation that innovation is often maximized in markets of moderate concentration.

Notes: In this paper we attempt to disentangle the effects of deregulation on rail costs from those directly attributable to mergers. We estimate that cost reductions obtained from mergers ranged from a high of 33% for the Burlington Northern to a low of a 3% cost increase for the CSX. However, firms not engaged in significant merger activities experienced similar cost differentials indicating that consolidation was not a prerequisite for cost savings. We conclude that although mergers did confer some benefits on the participating firms, they were not a prerequisite for railroads being able to achieve substantial cost savings.

Notes: For a homogeneous product oligopoly market, possibilities for pure strategy Nash equilibria in prices are studied. Consumers, who each nonstrategically purchase one unit up to a common reservation price, are hypothesized to be more concerned with large price differences (and therefore buy from the cheapest firm) than slightly different prices. For the duopoly case, existence, uniqueness, and characterization results are provided. Linear examples are given with 2 and n firms.

Notes: This paper analyzes the ongoing transformation of the soft drink distribution of Coca-Cola and Pepsi-Cola from systems of independent bottlers to captive bottling subsidiaries, A transaction cost-based theory is developed to explain this restructuring. It is postulated that changes in the external environment and the resulting changes in the strategies of Coca-Cola and Pepsi-Cola raised the costs of transacting between them and their independent bottlers. Two types of empirical tests are presented. One exploits the difference in the distribution of Coca-Cola and Pepsi-Cola in the fountain channel. The other consists of statistical analyses of the competitive effects of the move toward captive distribution. Both types of tests support the basic hypothesis.

Notes: The Cordilleran orogen in south-eastern Alaska includes 14 distinct metamorphic belts that make up three major metamorphic complexes, from east to west: the Coast plutonic–metamorphic complex in the Coast Mountains; the Glacier Bay–Chichagof plutonic–metamorphic complex in the central part of the Alexander Archipelago; and the Chugach plutonic–metamorphic complex in the northern outer islands. Each of these complexes is related to a major subduction event. The metamorphic history of the Coast plutonic–metamorphic complex is lengthy and is related to the Late Cretaceous collision of the Alexander and Wrangellia terranes and the Gravina overlap assemblage to the west against the Stikine terrane to the east. The metamorphic history of the Glacier Bay–Chichagof plutonic–metamorphic complex is relatively simple and is related to the roots of a Late Jurassic to late Early Cretaceous island arc. The metamorphic history of the Chugach plutonic–metamorphic complex is complicated and developed during and after the Late Cretaceous collision of the Chugach terrane with the Wrangellia and Alexander terranes.The Coast plutonic–metamorphic complex records both dynamothermal and regional contact metamorphic events related to widespread plutonism within several juxtaposed terranes. Widespread moderate-P/T dynamothermal metamorphism affected most of this complex during the early Late Cretaceous, and local high-P/T metamorphism affected some parts during the middle Late Cretaceous. These events were contemporaneous with low- to moderate-P, high-T metamorphism elsewhere in the complex. Finally, widespread high-P–T conditions affected most of the western part of the complex in a culminating late Late Cretaceous event. The eastern part of the complex contains an older, pre-Late Triassic metamorphic belt that has been locally overprinted by a widespread middle Tertiary thermal event.The Glacier Bay–Chichagof plutonic–metamorphic complex records dominantly regional contact-metamorphic events that affected rocks of the Alexander and Wrangellia terranes. Widespread low-P, high-T assemblages occur adjacent to regionally extensive foliated granitic, dioritic and gabbroic rocks. Two closely related plutonic events are recognized, one of Late Jurassic age and another of late Early and early Late Cretaceous age; the associated metamorphic events are indistinguishable. A small Late Devonian or Early Mississippian dynamothermal belt occurs just north-east of the complex. Two older low-grade regional metamorphic belts on strike with the complex to the south are related to a Cambrian to Ordovician orogeny and to a widespread Middle Silurian to Early Devonian orogeny.The Chugach plutonic–metamorphic complex records a widespread late Late Cretaceous low- to medium/high-P, moderate- T metamorphic event and a local transitional or superposed early Tertiary low-P, high-T regional metamorphic event associated with mesozonal granitic intrusions that affected regionally deformed and metamorphosed rocks of the Chugach terrane. The Chugach complex also includes a post-Late Triassic to pre-Late Jurassic belt with uncertain relations to the younger belts.

Notes: Small pods of silica-undersaturated Al-rich and Mg-rich granulite facies rocks containing sapphirine, pleonastic spinel, kornerupine, cordierite, orthopyroxene, corundum, sillimanite and gedrite are scattered throughout the NE Strangways Range, Central Australia. These are divided into four distinct rock types, namely orthopyroxene-rich aluminous granofels and metapelitic gneisses containing sapphirine, spinel or kornerupine. Two granulite facies metamorphic events are recognized, of which only the first (M1) is considered in this paper.Peak metamorphic mineral parageneses indicate that the M1 thermal maximum occurred at approximately 900–950 °C and 8–9 kbar. All samples are characterized by profuse and diverse coronitic and symplectic reaction textures. These are interpreted as evidence for the sequential crossing of the following reactions in the system FMAS:cordierite + spinel + corundum = sapphirine + sillimanite, cordierite + spinel = orthopyroxene + sapphirine + sillimanite, sapphirine + spinel + sillimanite = orthopyroxene + corundum, sapphirine + sillimanite = cordierite + orthopyroxene + corundum.Phase stability relationships in FMAS and MASH indicate an anticlockwise P–T path terminated by isobaric cooling. Such a path is exemplified by early low-P mineral parageneses containing spinel, corundum and gedrite and the occurrence of both prograde and retrograde corundum. Reaction textures preserve evidence for an increase in aH2O and aB2O3 with progressive isobaric cooling. This hydrous retrogression resulted from crystallization of intimately associated M1 partial melt segregations. There is no evidence for voluminous magmatic accretion giving rise to the high M1 thermal gradient. The M1 P–T path may be the result of either lithospheric thinning after both crustal thickening and burial of the supracrustal terrane, or concomitant crustal thickening and mantle lithosphere thinning.

Notes: The Seve–Köli Nappe Complex is widespread in the Scandinavian Caledonides and is composed of units representing parts of the Baltoscandian margin (Seve Nappes) now overlain by magmatic–sedimentary rocks (Köli Nappes) derived from west of this margin. The metamorphic evolution of Köli and Seve units has been studied in the Handöl area, central Scandinavian Caledonides, where a fragmented ophiolite with cover sequence in the lower Köli units is thrust over the higher grade Seve units. Thermobarometry constrains metamorphic conditions to 490–570° C/950–600 MPa, with a slight downwards increase in grade, for the lower Köli (Bunnerviken lens), 520–620° C/1000–600 MPa for the upper Seve (Täljstensvalen Complex), 630–740° C/750–650 MPa for the middle Seve (Snasahögarna Nappe) and 480–600° C/1150–1000 MPa for the lower Seve (Blåhammarfjället Nappe). P–T paths during garnet growth have been constructed for all units, except the highest grade middle Seve. These paths record heating at the base of the Köli and cooling in the underlying Seve units. Pressure increase during garnet growth is indicated for all units leading to anticlockwise P–T paths in the Seve. The results imply thermal convergence with time for all units and spatial convergence in metamorphic grade in the Köli. It is suggested that the contrasting metamorphic histories on either side of the Seve–Köli boundary resulted from the emplacement of relatively colder Köli rocks on top of relatively hotter Seve rocks and that emplacement of structurally higher units contributed to the increase in pressure.

Notes: Numerical and analytical models of fluid flow that account for fluid production during prograde regional and contact metamorphism show that expulsion of metamorphic fluids dominates the convective flux when crustal permeabilities are less than 0.1–100 μD, depending primarily on the rate of fluid production. When this is the case, fluid circulation is limited or prevented, fluid pressures are elevated above hydrostatic values, and flow throughout most of the model is up and away from the region of maximum fluid production. Fluid circulation is predicted to occur where permeability is high, in dry rocks, or after rates of fluid production decrease as peak temperatures are reached. Large changes in the pattern of flow and influx of externally derived fluids may thus occur in metamorphic terranes when dehydration wanes or ceases and cooling begins. Inclusion of an impermeable horizon in the models further inhibits fluid circulation. Earlier, shallow hydrothermal models and interpretations based on the Rayleigh number may be inappropriate for characterizing fluid flow during prograde metamorphism at depth because they do not account for fluid production.

Notes: An occurrence of quartz-eclogite is described from the Inner Schieferhülle unit of the Pennine Basement Complex in the SE Tauern Window, Austria.Field relations strongly suggest a pre-Alpine age for the primary eclogitic mineral assemblage (garnet + omphacite + quartz + rutile). This implies that there was no connection between the formation of these eclogites and the late Cretaceous and Tertiary tectonic evolution of the Eastern Alps. The quartz-eclogite mineral assemblage crystallized under conditions of 620 ± 100°C and at pressures in excess of 12 kbar, and suffered amphibolitic overprinting of Alpine and possibly Hercynian age.A four-stage polymetamorphic history is proposed for the Inner Schieferhülle:

Notes: Mafic and ultramafic xenoliths in a basaltic cone at The Anakies in south-eastern Australia are geochemically equivalent to continental basaltic magmas and cumulates. The xenolith microstructures range from recognizably meta-igneous for intrusive rocks to granoblastic for garnet pyroxenites. Contact relationships between different rock types within some xenoliths suggest a complex petrogenesis of multiple intrusive, metamorphic and metasomatic events at the crust/mantle boundary during the evolution of south-eastern Australia. Unaltered spinel lher-zolite, typical of the uppermost eastern Australian mantle, is interleaved with or veined by the metamorphosed intrusive rocks of basaltic composition.Geothermobarometry calculations by a variety of methods show a concordance of equilibration temperatures ranging from 880°C to 980°C and pressures of 12 to 18 kbar (1200-1800 mPa). These physical conditions span the gabbro to granulite to eclogite transition boundaries. The water-vapour pressure during equilibration is estimated to be about 0.5% of the load pressure, using amphibole breakdown data. Large fluid inclusions of pure CO2 are abundant in the mineral phases in the xenoliths, and it is suggested that flux of CO2 from the mantle has been an important heat source and fluid medium during metamorphism of the mafic and ultramafic protoliths at the lower crust/upper mantle boundary.The calculated pressures and temperatures suggest that the south-eastern Australian crust has sustained a high geothermal gradient. In addition, the nature of the mineral assemblages and the contact relationships of granulitic rock with spinel lherzolite, characteristic of mantle material, suggest that the Moho is not a discrete feature in this region, but is represented by a transition zone approximately 20 km thick. These inferences are in agreement with geophysical data (including seismic, heat-flow and electrical resistivity data) determined for south-eastern Australia.Underplating at the crust/mantle boundary by continental basaltic magmas may be an important alternative or additional mechanism to the conventional andesite model for crustal accretion.

Notes: We augment efficiency-based theories of ownership by including influence costs. Our principal conclusion is that the prospect of organizational decline and layoffs creates additional influence costs in multiunit organizations that would be absent if there was no prospect of layoffs and would be lessened or eliminated in focused organizations. This helps explain the tendency of firms to divest poorly performing units, as well as the pattern of sales of such units to firms already in businesses related to that of the divested unit.

Notes: The Lewisian of Tiree, north-west Scotland, underwent granulite facies metamorphism prior to 2.4 Ga. The temperatures and pressures estimated from garnet–clinopyroxene, garnet–orthopyroxene, hornblende–plagioclase and garnet–biotite geothermometers and clinopyroxene–plagioclase–garnet–quartz and orthopyroxene–plagioclase–garnet–quartz geobarometers are 810 ± 50° C and 10.5 ± 1.5 kbar. The imprecision of pressure estimates stems largely from uncertainties in garnet activity models. Calculations of blocking temperatures for Fe–Mg interdiffusion in clinopyroxene and garnet suggest that these temperatures and pressures represent only slightly reset peak-metamorphic conditions.Down-temperature re-equilibration resulted in chemical zoning over the outer 50–100 μm of the mafic minerals. P–T paths calculated from this mineralogical zoning suggest nearly isobaric cooling. However, the growth of late sillimanite in metapelites requires that the retrograde P–T path had a significant decompression component, suggesting that the mineralogical zonation does not define the retrograde P–T path. The discrepancy between the P–T path calculated from mineralogical zonation and that implied by mineral reactions probably results from the net-transfer geobarometry reactions closing at higher temperatures than the exchange geothermometers.The Tiree rocks have a similar history to the mainland Scourian complex. Granulite facies metamorphism accompanied by partial melting occurred prior to the intrusion of the Scourie dykes at c. 2.4 Ga, and the rocks underwent retrogression both prior to and after dyke emplacement. However, peak metamorphic temperatures and pressures on Tiree were lower than those recorded in the Scourian complex, and the Tiree rocks may have been at a different crustal level at that time.

Notes: Estimated variations in mineral concentrations across leucosomes suggest that leucosomes are generated during anatexis by a diffusive exchange between the leucosome and the mesosome, and not by the migration of melt from the mesosome. However, the presence of melt is a precondition for the diffusive exchange to take place. Initially a crack is formed due to shear stress. The formation of a crack allows a diffusive exchange to take place through the melt, which causes melting of minerals situated near the crack. The diffusive exchange of material is less efficient in the mesosome where the melt is isolated at grain corners and edges. The microcline enrichment of some granitic leucosomes is thought to be due to the diffusive depletion of the mesosome caused by growth of alkali feldspar during the consolidation of the migmatite. In general, it seems unnecessary to invoke concentrations of water in the leucosome or the intrusion of external fluids or magmas for migmatite formation.

Notes: The proposed geothermobarometer is based on an empirical calibration which takes account of two equilibria involving the tremolite, edenite, pargasite and hastingsite components in amphiboles. It has applications to assemblages found in metabasic rocks of widely different chemical compositions (magnesian to Fe-rich metabasalts), and for metamorphism ranging from lower greenschist to highest amphibolite facies. Knowing the Si(T1), Aliv, Alvi, Fe3+, Fe2+, Mg, Ca, NaM4, NaA and A vacancy in an amphibole, and the Al3+ and XMg in coexisting epidote and chlorite, it is possible to calculate two values of In Kd for this assemblage. These equilibria involve edenite-tremolite and (pargasite/hastingsite)-tremolite end-members in amphibole (the calculation program is given). For these equilibria, the isopleths (iso-values of Kd) have been calculated for 0.27 〈 XMg 〈 0.75 and 0 〈 XFe3+= Fe3+/(Fe3++ Alvi) 〈 0.8. It is then possible to determine pressure and temperature directly when XMg, XFe3+, In Kd for tremoliteedenite and In Kd for (pargasite/hastingsite)-tremolite are known. Application of this geothermobarometer is limited to Ca-free plagioclase assemblages, and complete P–T paths can be drawn only if all the minerals are considered together. Phase relations at successive stages of crystallization can be constrained by studying the relationships between the coexisting minerals, their zoning and the metamorphic fabrics.

Notes: Abstract. In the Kamuikotan zone, central Hokkaido, Japan, two distinct types of metamorphic rocks are tectonically mixed up, along with a great quantity of ultramafic rocks; one type consists of high-pressure metamorphic rocks, and the other of low-pressure ones. The high-pressure metamorphic rocks are divided into two categories. (1) Prograde greenschist to glaucophaneschist facies rocks derived from mudstone, sandstone, limestone, a variety of basic rocks such as pillow and massive lavas, hyaloclastite and tuff, and radiolarian (Valanginian to Hauterivian) chert, among which the basic rocks and the chert, and occasionally the sandstone, occur as incoherent blocks (or inclusions) enveloped by mudstone. (2) Retrograde amphibolites with minor metachert and glaucophane-calcite rock, which are tectonic (or exotic) blocks enclosed within prograde mudstone or serpentinite, or separated from these prograde rocks by faults. The K-Ar ages of the prograde metamorphic rocks (72, 107 and 116 Ma on phengitic muscovites) are younger than those of the retrograde rocks (109, 132, 135 and 145 Ma on muscovites, and 120 Ma on hornblende). The low-pressure metamorphic rocks consist of the mafic members of an ophiolite sequence with a capping of radiolarian (Tithonian) chert with the metamorphic grade ranging from the zeolite facies, through the greenschist (partly, actinolite-calcic plagioclase) facies to the amphibolite (partly, hornblende-granulite) facies. The low-pressure metamorphism has a number of similarities with that described for‘ocean-floor’metamorphism. The tectonic evolution of such a mixed-up zone is discussed in relation to Mesozoic plate motion.

Notes: The rocks of the Scourian Complex have been intensively studied, but there is still no consensus as to the conditions of the granulite-facies metamorphism preserved in these rocks. Recent estimates of these conditions fall into two groups, one at 820-920°C and ca. 11 kbar and the second at ca. 1000°C and 〉12 kbar. Investigation of a variety of rocks shows that the recorded conditions vary with grain-size, with higher-grade conditions recorded by the cores of coarser (ca. 10 mm) crystals, and lower-grade conditions recorded by the rims of coarser grains and by finer grains. This observation suggests that re-equilibration during recovery of these rocks to the surface has been important which may account for the discrepancy in estimated P-T conditions. Revised estimates of the equilibration conditions of the Scourian Complex of T 〉 1000°C and P 〉 8.5 kbar are presented. The conditions suggested for the peak of metamorphism mean that the role of anatexis in the genesis of these rocks must be considered and the nature of the fluid phase thoroughly investigated.

Notes: The Whitestone Anorthosite (WSA), located in the Central Gneiss Belt of the south-western Grenville Province, Ontario, exhibits a nearly concentric metamorphic envelope characterized by an increase in modal scapolite, hornblende, epidote and garnet, developed around a core of granulite facies clinopyroxene ± orthopyroxene ± garnet meta-anorthosite. Scapolite- and hornblende-bearing assemblages develop mainly at the expense of plagioclase and pyroxene within the envelope.Stable isotopic and petrological data for scapolite-bearing mineral assemblages within meta-anorthosite constrain the source of carbon responsible for CO3-scapolite formation and the extent of fluid/rock interaction between the anorthosite and adjacent lithologies. Stable isotopic data indicate increasing δ18O and δ13C from core to margin of the meta-anorthosite and for samples from the southern extension of the WSA, where it is ductilely deformed within the Parry Sound Shear Zone (PSSZ). The average δ18OSMOW value (whole rock) for the WSA core is 6.9‰, increasing to 11.5‰ where the WSA is in tectonic contact with marble breccia. The average δ13CPBD value of scapolite in meta-anorthosite from the centre of the WSA is -3.4‰, increasing to -0.5‰ at the eastern (marble) contact. Average values of δ13C for scapolite and whole-rock δ18O for samples from the shear zone are -1.0 and 8.0‰, respectively. Marbles have average δ18O and δ13C values of 19.2 and -0.4‰, respectively.The sulphate content of texturally primary scapolite decreases from the core of the WSA (XSO4= 0.48) to the eastern contact (≤0.05). Texturally late scapolite after plagioclase and garnet tends to be CO3-rich relative to texturally primary scapolite, and some scapolite grains show zoning in the anion site with CO3-enriched rims. Scapolite composition may vary at any scale from a single grain to outcrop.The pattern of isotopic enrichment in 13C and 18O preserved in the eastern margin of the WSA is consistent with marble as the major source of fluid contributing to the formation of the metamorphic envelope. The decrease in XSO4 and increase in XCO3 in scapolite toward the margin of the WSA indicate that the volatile content was reset by, or developed from, a CO2-bearing fluid. Assuming derivation of fluid from marble, minimum fluid/rock values at the margin of the WSA range from 0.03 for the least enriched, to 0.30 for the most isotopically enriched samples. Although marble is not found in immediate contact with samples of sheared meta-anorthosite from the PSSZ, a marble source is also consistent with the C and O isotope composition and anion chemistry of scapolite within these samples.

Notes: The equilibrium constant, Ka, of the association reaction to form ion pairs from charged solute species in supercritical solutions can be calculated from a model based on published equations. Log Ka at constant pressure is a linear function of the inverse in the dielectric constant of the fluid times temperature. The dielectric properties of H2O and CO2 at supercritical pressures and temperatures can also be evaluated using the Kirkwood equation. Using Looyenga mixing rules, the dielectric constant of H2O–CO2 mixtures can be obtained and the change in log Ka with addition of CO2 in aqueous solutions evaluated. These changes in log Ka with addition of CO2 are consistent with measured changes of log Ka with addition of Ar in supercritical H2O–Ar solutions.Log Ka of KCl and NaCl increase to an increasing extent as the mole fraction of CO2 increases in H2O–CO2 solutions. For instance, at 2 kbar and constant temperature between 400 and 600° C, log Ka of KCl increases by about two orders of magnitude whilst that of NaCl increases by over four orders of magnitude as the CO2 mole fraction increases from 0.0 to 0.35. Such changes in log Ka will have dramatic effects on the solubility of minerals in CO2-rich environments.

Notes: Regional metamorphism in the Sulitjelma area of the arctic Scandinavian Caledonides has produced a series of Barrovian zones, from chlorite through to kyanite in more aluminous pelites, which transect the major lithological boundaries in a large nappe unit of the Köli Nappe Complex. The metamorphic zones are inverted, and metamorphic grade increases westwards from the foreland to the hinterland. The Furulund Group comprises a mixed sequence of originally flysch-like sediments which crop out over the whole range of the observed Barrovian zones, but are usually too calcareous to develop the characteristic Barrovian aluminous phases staurolite and kyanite. Instead, above the garnet isograd, the Furulund Group pelites and semi-pelites have widely developed hornblende porphyroblasts in the common assemblage Grt + Pl + Bt + Ms + Qtz ± Hbl ± Ep ± Czo ± Chl ± Cal ± Dol. Thermobarometric estimates of metamorphic peak P–T conditions (i.e. at maximum recorded temperatures) from this assemblage, using three different methods, indicate a westward increase of both pressure and temperature over a distance of 14 km away from the garnet isograd towards the hinterland of the orogen, independent of topographic level and without change in the common mineral assemblage. The increased peak pressure in the west indicates greater initial burial and subsequent exhumation in the hinterland than towards the foreland. Restoration indicates that the Furulund Group has been subjected to substantial eastward bulk tilting after peak metamorphic conditions. Whilst this enhances the overturning of the metamorphic zones, the amount of tilting was not sufficient to cause the overturning.

Notes: The sequence of growth of garnet, staurolite and aluminosilicate in Fe-rich metapelitic rocks from the Canigou massif, Pyrenees, is established using evidence of inclusion, reaction and pseudomorphing textures between the different minerals, compositional zoning patterns in garnet and staurolite (that can be related to the KFMASH reaction grid), and the geometric relations between inclusion trails in the porphyroblasts and the matrix microstructures. The evidence indicates that garnet and staurolite commenced growth before aluminosilicate in all cases, even where all three are in textural equilibrium. Interpretation of the reaction textures between the porphyroblasts and of the compositional zoning in garnet and staurolite in terms of the KFMASH reaction grid indicates the importance of continuous reactions in the development of these phases. Some garnet and staurolite porphyroblasts underwent renewed growth during breakdown, producing rims enriched in Mn and Zn respectively. The presence of aluminosilicate in these assemblages (i.e. the absence of a clear andalusite-absent zone in the field) is attributed to a strong pressure-dependence for the aluminosilicate-producing reactions. Porphyroblast-matrix microstructural relations indicate that Hercynian metamorphism in the massif was synchronous with the development of the regional subhorizontal foliation (S3).

Notes: The metamorphic history of mafic exotic blocks from a tectonic melange zone within an allochthonous ophiolitic terrane (Marmora Terrane) of the Pan-African Gariep orogenic belt in south-western Namibia was studied, based on mineral parageneses and amphibole composition. Glaucophane described previously from these rocks could not be verified. Instead, two types of blue amphiboles were distinguished: (i) rims of (ferro-) edenitic to pargasitic to barroisitic hornblende composition around brownish amphibole phenocrysts replacing magmatic clinopyroxene, and (ii) deep blue porphyroblasts of magnesio-riebeckite with little ferro-glaucophane component in a highly metasomatized albite-rich rock. Textural and mineralogical evidence, particularly the existence of up to three different amphibole generations in metagabbro samples, supports a multiphase metamorphic history experienced by these exotic blocks. The first metamorphic event, M1, is interpreted as very low-P hydrothermal oceanic metamorphism that affected the igneous protoliths at up to amphibolite facies temperatures. Subsequent M2 metamorphism was syntectonic and is characterized by temperatures similar to those attained during M1 but higher pressures indicating burial to 15–20 km. This event is related to a subduction process. The third metamorphic event, M3, was low grade and of regional nature. It is the only one recorded in the sedimentary envelope of the exotic blocks. The formation of magnesio-riebeckite is considered a retrograde reaction at greenschist facies during M2. The results indicate that in the Gariep belt subduction and subsequent obduction have occurred, although blueschist facies metamorphism has not been reached.

Notes: New data strongly suggest that the classical spiral garnet porphyroblasts of south-east Vermont, USA, generally did not rotate, relative to geographical coordinates, throughout several stages of non-coaxial ductile deformation. The continuity of inclusion trails (Si) in these porphyroblasts is commonly disrupted by planar to weakly arcuate discontinuities, consisting of truncations and differentiation zones where quartz–graphite Si bend sharply into more graphitic Si. Discontinuous, tight microfold hinges with relatively straight axial planes are also present. These microstructures form part of a complete morphological gradation between near-orthogonally arranged, discontinuous inclusion segments and smoothly curving, continuous Si spirals. Some 2700 pitch measurements of well-developed inclusion discontinuities and discontinuous microfold axial planes were taken from several hundred vertically orientated thin sections of various strike, from specimens collected at 28 different locations around the Chester and Athens domes. The results indicate that the discontinuities have predominantly subvertical and subhorizontal orientations, irrespective of variations in the external foliation attitude, macrostructural geometry and apparent porphyroblast-matrix rotation angles. Combined with evidence for textural zoning, this supports the recent hypothesis that porphyroblasts grow incrementally during successive cycles of subvertical and subhorizontal crenulation cleavage development. Less common inclined discontinuities are interpreted as resulting from deflection of anastomosing matrix foliations around obliquely orientated crystal faces prior to inclusion. Most of the idioblastic garnet porphyroblasts have a preferred crystallographic orientation. Dimensionally elongate idioblasts also have a preferred shape orientation, with long axes orientated normal to the mica folia, within which epitaxial nucleation occurred.Truncations and differentiation zones result from the formation of differentiated crenulation cleavage seams against porphyroblast margins, in association with progressive and selective strain-induced dissolution of matrix minerals and locally also the porphyroblast margin. Non-rotation of porphyroblasts, relative to geographical coordinates, suggests that deformation at the microscale is heterogeneous and discontinuous in the presence of undeformed, relatively large and rigid heterogeneities, which cause the progressive shearing (rotational) component of deformation to partition around them. The spiral garnet porphyroblasts therefore preserve the most complete record of the complex, polyphase tectonic and metamorphic history experienced in this area, most of which was destroyed in the matrix by progressive foliation rotation and reactivation, together with recrystallization.

Notes: Extensive examination of large numbers of spatially orientated thin sections of orientated samples from orogens of all ages around the world has demonstrated that porphyroblasts do not rotate relative to geographical coordinates during highly non-coaxial ductile deformation of the matrix subsequent to their growth. This has been demonstrated for all tectonic environments so far investigated. The work also has provided new insights and data on metamorphic, structural and tectonic processes including: (1) the intimate control of deformation partitioning on metamorphic reactions; (2) solutions to the lack of correlation between lineations that indicate the direction of movement within thrusts and shear zones, and relative plate motion; and (3) a possible technique for determining the direction of relative plate motion that caused orogenesis in ancient orogens.

Notes: The field relations from a quarry at Nuliyam, South India, illustrate dehydration of an amphibolite facies gneiss to granulite facies charnockite by CO2 influx, over a scale of 30 m. Both the calc-silicate source of the fluids and the full extent of their penetration into the gneiss are preserved in a continuous section. Fluid flow is by a hydraulic fracture mechanism, but is thought to be pervasive. The sharp reaction front predicted by the continuum mechanical theory for advective fluid transport is not observed. The front spreading is on too large a scale for either diffusive or dispersive control and is due to local kinetic disequilibrium between the fluid and rock, although the divariant nature of the reaction may also have a limited effect. The time-integrated fluid flux varies from the instantaneous porosity at the fluid front to 20 vol. % adjacent to the calc-silicate. Carbon isotope budgets suggest that decarbonation of the calc-silicate by a Rayleigh fractionation process provides a sufficient source for the CO2 influxing into the gneiss. Graphite abundances vary from 0.01 to 0.1% (by weight), it is principally derived by precipitation from the fluid and may be modelled from phase equilibria. Carbon isotope fronts coincide with the reaction front on the scale of sampling, although isotopic disequilibrium between graphite and inclusion-CO2 also implies local fluid-rock disequilibrium.

Notes: A high-grade Archaean gneiss terrane in the northern Gallatin Range, south-western Montana, USA, contains a trondhjemite–tonalite gneiss (TTG) sequence that was migmatized during pervasive ductile shearing. Metamorphism of these rocks is in the upper amphibolite to granulite facies at temperatures of 680–735°C, pressures in excess of 8 kbar, and a ‘clockwise’P–T–t path is inferred. Ductile shearing occurred in metre-scale anastomosing bands of high strain throughout the area. The TTGs have been extensively migmatized via vapour-present melt reactions involving the incongruent melting of biotite-bearing TTG to produce hornblende and granitic melt. The granitic melt is produced in narrow envelopes adjacent to ductile shear zones in response to infiltration of water-rich solutions. Melt migration occurred on a local scale, and extraction of melt from the system left behind a plagioclase–hornblende residuum with minor interstitial microcline. Ductile shearing and migmatization in the TTG operated in a positive feedback mechanism; the entire volume of gneiss was chemically and mechanically reworked through the cyclical infiltration of aqueous solutions, vapour-present melting and melt-enhanced deformation. The proposed melt reaction may be an important crustal differentiation process considering that (1) many collisional orogens do not attain temperatures high enough to permit vapour-absent melting, (2) pervasive networks of ductile shear zones at mid-crustal levels may serve as channels for fluid ingress and melt extraction, and (3) the large volumes of TTGs in Archaean and Phanerozoic orogens may constitute a significant source reservoir for certain types of high-level granites.

Notes: In the Southern Alps a progressive metamorphic zonation, with an increase in the geothermal gradient from NE to SW, has been widely proposed. However, recent investigations have shown that the greenschist metamorphic imprint of the low-grade zone corresponds to a metamorphic retrogression following amphibolite facies conditions. On the other hand, in the medium-grade zone, a later low-pressure, high-temperature (LPHT) metamorphic event has also been proposed. In an attempt to resolve these different interpretations, new petrological and partly new structural data have been obtained for two sectors of the Orobic Alps, traditionally attributed to different metamorphic zones. Thermobarometric determinations, supported by microstructural analysis, indicate the following different pressure-retrograde paths in each sector: (1) in the Val Vedello basement (VVB) rocks, a first metamorphic imprint characterized by P= 7–9 kbar and T= 570–610°C was followed by a greenschist retrogression (P≤ 4 kbar and T≤ 500° C); (2) in the Lario basement (LB) rocks, the first detectable metamorphic stage, characterized by mineral assemblages indicating P= 7–9 kbar and T= 550–630° C, was followed by a LPHT event, synkinematic with F2 extensional deformation. A greenschist retrogression marks the final uplift of these rocks.Reinterpretation of the available geochronological data indicates a diachronism for the two thermomechanical evolutions. In the light of these data, we interpret the retrograde P–T–t path of the VVB rocks as a pre-Permian post-thickening uplift and the retrograde P–T–t evolution of the LB rocks as a Permo-Mesozoic uplift related to the extensional tectonic regime of the Tethyan rifting.

Notes: The eastern Central Alps consist of several Pennine nappes with different tectonometamorphic histories. The tectonically uppermost units (oceanic Avers Bündnerschiefer, continental Suretta and Tambo nappes, oceanic Vals Bündnerschiefer) show Cretaceous/early Tertiary W-directed thrusting with associated blueschist facies metamorphism related to subduction of the Pennine units beneath the Austroalpine continental crust. This event caused eclogite facies metamorphism in the underlying continental Adula nappe. The gross effect was crustal thickening. The tectonically lower, continental Simano nappe is devoid of any imprint from this event. In the course of continent-continent collision, high-T metamorphism and N-directed movements occurred. Both affected the whole nappe pile more or less continuously from amphibolite to greenschist facies conditions. Crustal thinning commenced during the regional temperature peak. A final phase is related to differential uplift under retrograde P–T conditions. Further thinning of the crust was accommodated by E- to NE-directed extensional deformation.