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  • 1
    Electronic Resource
    Electronic Resource
    Hawaiite of High Pressure Origin from North-eastern New South Wales (1969)
    [s.l.] : Nature Publishing Group
    Nature 222 (1969), S. 553-555 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The hawaiite flow is exposed in a quarry about 2 miles l east of Kyogle on the road to Nimbin, in far north-eastern New South Wales. The host rook (Table 1) can be designated as a comparatively iron-poor hawaiite approaching mugearite in composition (K2O/Na2O = 0-38; normative plagioclase = 33-2 ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/222553a0
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  • 2
    Electronic Resource
    Electronic Resource
    Trace element fractionation trends of tholeiitic magma at moderate pressure: Evidence from an Al-spinel ultramafic-mafic inclusion suite (1981)
    Springer
    Contributions to mineralogy and petrology 75 (1981), S. 225-233 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Trace element data on an Al-spinel ultramafic-mafic inclusion suite in an analcimite support earlier proposals that the various inclusions are comagmatic and represent fragments of a layered tholeiitic ‘pluton’ which differentiated at pressures close to 8 kb. Ultramafic inclusions are dominantly pyroxenites, often websteritic, whereas the mafic inclusions are largely two pyroxene-plagioclase assemblages. Appropriate experimental data and abundances of Sc, Cr and V indicate that subcalcic clinopyroxene or relatively Ca-rich clinopyroxene was the major ferromagnesian phase fractionated, often accompanied by spinel in the early and middle stages of differentiation and, in the later stages, by titanomagnetite. Comparatively moderate decreases in Ni and Co suggest that olivine was a relatively unimportant fractionating phase. Clinopyroxene fractionation at moderate pressures should be assigned only a comparatively insignificant role in the production of evolved basaltic compositions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01166762
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  • 3
    Electronic Resource
    Electronic Resource
    Tholeiitic andesite of high-pressure origin from the tweed shield volcano, northeastern New South Wales (1973)
    Springer
    Contributions to mineralogy and petrology 39 (1973), S. 267-276 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract A high-alumina tholeiitic andesite from the southern portion of the Tweed Shield Volcano in northeastern New South Wales contains abundant megacrysts of plagioclase (Ab50An46Or4) and “megacrysts” of aluminian bronzite (Ca4Mg71Fe25) and relatively Ca-poor aluminian augite (Ca36Mg41Fe20). The pyroxenes commonly occur as inclusions in the plagioclase megacrysts. Electron probe microanalyses of the pyroxene megacrysts indicate that they differ in character and composition from the groundmass ferromagnesian phases, namely a more Al- and Na-poor augite (Ca41Mg42Fe17) and olivine (Fa53). The bulk composition of the plagioclase megacrysts is slightly more Ab-rich than that of the groundmass plagioclase, but differences in the two compositions are extended by microanalyses of groundmass plagioclases. Evaluation of the megacryst compositions in the light of experimental data and analogous occurrences in alkaline volcanics leads to the interpretation that the megacrysts represent cognate precipitates formed at pressures broadly equivalent to the crust-mantle boundary. More important, they provide strong evidence for the high pressure origin of tholeiitic andesites, customarily interpreted as the products of low pressure fractional crystallization of tholeiitic magma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00376467
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  • 4
    Electronic Resource
    Electronic Resource
    Ultramafic inclusions and high pressure megacrysts from a nephelinite sill, Nandewar Mountains, north-eastern New South Wales, and their bearing on the origin of certain ultramafic inclusions in alkaline volcanic rocks (1975)
    Springer
    Contributions to mineralogy and petrology 51 (1975), S. 235-262 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Ultramafic inclusions and megacrysts are unusually abundant in a nephelinite sill in the Nandewar Mountains in north-eastern New South Wales. The inclusions are divisible into a Cr-diopside group and a Ti-augite group, the former being dominated by Cr-spinel Iherzolites of restricted modal composition, the latter by olivine and titaniferous Al-rich clinopyroxene assemblages which vary widely in their modal proportions. The principal megacryst species are olivine and black, titaniferous Al-rich clinopyroxene; additional but comparatively rare megacrysts include titanphlogopite, kaersutitic amphibole, and deep green, relatively Fe-rich clinopyroxene. The Cr-spinel Iherzolites conform closely in mineralogy and chemistry with the spinel lherzolites which dominate upper mantle xenolith assemblages in alkaline mafic volcanic rocks from other provinces. Megacrysts and Ti-augite inclusion mineral assemblages are consistently more Fe-rich than analogous phases in the Cr-diopside xenoliths and also display more extensive cryptic variation. The available experimental data on the high pressure liquidus or near-liquidus phases in olivine nephelinite and related compositions indicate that the olivine and black clinopyroxene megacrysts were precipitated at pressures in the vicinity of 15–20 kb. The similarity in the nature and compositions of the principal megacryst species to analogous phases in the Tiaugite group of inclusions indicates that the latter also represent cognate cumulates derived from the olivine nephelinite at broadly comparable pressures. High pressure fractionation of the host olivine nephelinite liquid, controlled mainly by the separation of olivine and aluminous clinopyroxene, produced only comparatively minor compositional changes in the derivative liquid. The hiatus in olivine compositions at approximately Fo86–88, apparently characteristic of the olivines in coexisting Cr-diopside and Ti-augite inclusions, is assessed in terms of the compositions of olivine in equilibrium with alkali basaltic liquids at high pressures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00372144
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  • 5
    Electronic Resource
    Electronic Resource
    An Al-spinel ultramafic-mafic inclusion suite and high pressure megacrysts in an analcimite and their bearing on basaltic magma fractionation at elevated pressures (1975)
    Springer
    Contributions to mineralogy and petrology 53 (1975), S. 71-104 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract An analcimite sill, which intrudes Carboniferous sedimentary rocks northwest of the township of Barraba in northeastern New South Wales, is exceedingly rich in ultramafic and mafic inclusions and also contains a varied megacryst assemblage. The majority of inclusions belong to an ultramafic-mafic granulite suite whose members generally contain a Cr-poor green spinel. Layering is preserved in many inclusions and their textures are appropriate to those arising from recrystallization at subsolidus temperatures. Ultramafic granulites of the Al-spinel suite are mainly pyroxenites, with rarer lherzolites, and mafic granulites usually consist of the assemblage plagioclasea-luminous pyroxenes-spinel. Ca-rich tschermakitic clinopyroxenes and coexisting aluminous Ca-poor orthopyroxenes define a trend of moderate iron enrichment. Spinels also display significant Fe2+ → Mg substitution. Plagioclase in some plagioclase-bearing pyroxenites and mafic granulites contains numerous rod-like inclusions of spinel, compositionally similar to the discrete spinels unassociated with plagioclase. The formation of spinel in plagioclase is believed to have resulted largely from the migration of (Mg, Fe2+) to Al-rich nucleation sites in the feldspar. Other inclusion types include Cr-spinel lherzolites —more Fe-rich than Cr-diopside lherzolite inclusions in alkaline volcanics — and rare wehrlite heteradcumulates, probably cognate with the host analcimite. The megacryst assemblage is dominated by anorthoclase megacrysts, which are accompanied, in order of decreasing abundance, by megacrysts of tschermakitic clinopyroxene, titanbiotite, kaersutite, and aluminous titanomagnetite. The Al-spinel mafic granulites have low Ti, K and P contents and their petrochemical affinities are high-alumina mafic alkaline to transitional. They compare closely in major and minor element chemistry with some ocean ridge basalts. The Al-spinel ultramafic-mafic inclusions suite is interpreted as the remnants of a layered ultramafic-mafic “pluton ” which initially crystallized at pressures in the vicinity of 10 kb and subsequently re-equilibrated at subsolidus temperatures (ca 950° C) and comparable pressures. The parent magma was K-poor, ol-normative subalkaline and its fractionation at moderate pressures, controlled mainly by olivine and subcalcic clinopyroxene, resulted in decreases in the derivative liquids in their saturation levels and ol contents, and increases in Al and Ca. These trends are reflected in the compositions of the mafic granulites. The pressure regime of megacryst formation apparently was greater than 10–12 kb i.e. the megacrysts precipitated before acquisition of xenoliths of the Al-spinel granulite suite by the analcimite host. Anorthoclase fractionation produced only limited compositional changes in the original alkali basaltic melt.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00373125
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  • 6
    Electronic Resource
    Electronic Resource
    Some subcalcic clinopyroxenites from Salt Lake Crater, Oahu, and their petrogenetic significance (1976)
    Springer
    Contributions to mineralogy and petrology 58 (1976), S. 181-201 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Some inclusions from Salt Lake Crater are essentially single-phase subcalcic clinopyroxenites whose original clinopyroxenes, prior to extensive unmixing, were tschermakitic subcalcic varieties with compositions close to Ca34Mg54Fe12. In addition to copious amounts of orthopyroxene, very minor garnet and spinel also were exsolved from the subcalcic clinopyroxenes. The genesis of the garnet pyroxenite suite at Salt Lake Crater has been examined in terms of three models, namely: (i) cumulates from alkali basaltic magmas; (ii) fractional fusion of “basanitic” garnet clinopyroxenite; and (iii) anatexis of upper mantle lherzolites. Field, mineralogical, chemical and experimental data collectively favour model (iii) and indicate that the nodules are genetically unrelated to their nephelinitic hosts. The Salt Lake garnet pyroxenites can be closely equated with the garnet pyroxenites in magmatictype layers in certain alpine-type ultramafic massifs and they are also similar to many garnet pyroxenite xenoliths in alkaline volcanics from other localities. Liquids produced by anhydrous partial melting of spinel Iherzolite at pressures of approximately 20 kb commonly have picritic chemistries. The crystallization behaviour of picritic liquids at elevated pressures (∼ 20 kb) indicates that the initial crystallization products may be either essentially single-phase subcalcic clinopyroxenites (with minimal high pressure fractionation) or a range of olivine-aluminous orthopyroxene-aluminous subcalcic clinopyroxene-garnet-(spinel) assemblages with variable 100 Mg/(Mg+Fe) ratios (when fractionation has been operative). All these assemblages may be subsequently modified by subsolidus exsolution and recrystallization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00382184
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  • 7
    Electronic Resource
    Electronic Resource
    The Salt Lick Creek layered intrusion, East Kimberley region, Western Australia (1975)
    Springer
    Contributions to mineralogy and petrology 50 (1975), S. 1-23 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The Lower Proterozoic Salt Lick Creek intrusion, East Kimberley region, Western Australia, is a layered intrusion divisible into two well-defined zones, the Basal and Main Zones, whose combined stratigraphic thickness, as now exposed, is approximately 1000 metres. The Basal Zone, 360 metres thick, contains three members, two of which (Members 1 and 3) are dominated by olivine, plagioclase cumulates (including harrisites and allivalites); Member 2, near the middle of the Basal Zone, consists substantially of more olivine-rich cumulates, including plagioclase-bearing dunites. The Main Zone, commencing with Member 4 plagioclase, orthopyroxene cumulates, is composed largely of anorthositic cumulates of Member 5. Mild but nevertheless measurable rhythmic layering is superimposed upon the three members comprising the Basal Zone. Electron probe microanalyses of the primary phases across some 500 metres of cumulates indicate limited cryptic variation with stratigraphic height. Olivine ranges in composition from Fo81 to Fo84, orthopyroxene from Ca2Mg83Fe15 to Ca2Mg78Fe20, clinopyroxene from Ca48Mg46Fe6 to Ca44Mg48Fe8, and plagioclase from An84 to An88 but mineral compositions are not a simple function of stratigraphic height. It is inferred that the parental magma(s) was high-alumina mafic, intrinsically subalkaline, strongly olivine- and plagioclase-normative and in all likelihood tholeiitic in its affinities. The olivine-free cumulates of the Main Zone display a higher level of normative saturation than the cumulates of the Basal Zone but mineral and host rock chemistries, particularly 100 Mg/ (Mg+Fe2+) atomic ratios, are not favourable to proposals which would relate the origin of the Main Zone or the several members of the intrusion to the differentiation of a single pool of magma. It is suggested that the Main Zone, at least, derived from a separate pulse of relatively more saturated magma and that the lateral replenishment by more or less undifferentiated magma was also a fundamental and critical factor in the genesis of the Basal Zone cumulates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00385218
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  • 8
    Electronic Resource
    Electronic Resource
    Nephelines and analcimes in some alkaline igneous rocks (1994)
    Springer
    Contributions to mineralogy and petrology 118 (1994), S. 79-91 
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    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The paper presents electron microprobe analyses of nephelines and analcimes in alkaline igneous rocks ranging from theralite and basanite to mugearite and tinguaite. With few exceptions, the nephelines are Si-rich types whose Qz (quartz) components exceed those defining the limits of excess SiO2 in solid solution in the Ne-Ks-Qz-H2O system at 700°C and 1 kbarP H 2 O. Unlike the nephelines in the basanites which show only limited grain-to-grain compositional variation, those in theralites and tinguaites from the differentiated Square Top intrusion, New South Wales, and in a New Zealand tinguaite vary significantly in Ne (nepheline), Ks (kalsilite) and Qz, even within individual samples, and they also may be strongly zoned. The rims of zoned nephelines are enriched in Si and Fe3+, relative to core compositions. These zoning trends contrast with the composional trend of successive “bulk” nepheline fractions in the Square Top sequence theralite → tinguaite whereby Qz decreases. The nephelines coexist with high-temperature alkali feldspars. In the Ne-Ks-Qz system they plot on the Ne side of the Barth compositional join defined by the omission solid solution series with end-members K2Na6Al8Si8O32 (the Buerger ideal composition; Ne75Ks25 mol%) and □2Na6Al2Si10O32 (□=cavity cation vacancy). The compositions of most natural nephelines are restricted to the field defined by Ne and the Barth join, compositions more K-rich than the ideal composition being relatively rare. The compositions of nephelines on the Ne side of the join are controlled by a number of factors which include the physical conditions attending nepheline crystallization and the compositions of the alkaline hosts. Interstitial analcimes from the Square Top intrusion display extensive NaAl⇌Si substitution and their compositions extend from analcime of natrolite composition to compositions slightly more Si-rich than “ideal” NaAlSi2O6. Groundmass analcimes in the basanites, mugearite and New Zealand tinguaite have relatively constant compositions which approach stoichiometric NaAlSi2O6. An unusually Si-rich deuteric analcime (60.2% SiO2) is also present in vugs in the New Zealand tinguaite. Experimental and other evidence, includingP/T data defining the coexistence of analcime and silica-undersaturated silicate melt in the NaAlSiO4-KAlSiO4-SiO2-H2O system, and inferred solidus temperatures of the various hosts (they would have exceeded the stability range of analcime) preclude a primary magmatic origin for the interstitial and groundmass analcimes. These are interpreted as subsolidus phases produced by nepheline interaction with deuteric and/or hydrothermal fluids. Analyses of nephelines and their derivative analcimes indicate that the latter may form from both Si-rich and more Si-poor nephelines.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00310612
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  • 9
    Electronic Resource
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    Subcalcic clinopyroxenites and associated ultramafic xenoliths in alkali basalt near Glen Innes, northeastern New South Wales, Australia (1997)
    Springer
    Contributions to mineralogy and petrology 127 (1997), S. 272-290 
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    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract An alkali basalt near Glen Innes, northeastern New South Wales, contains a suite of Cr-diopside group ultramafic xenoliths which includes some spinel peridotites but which is dominated by a diverse spinel pyroxenite assemblage. Pyroxenite xenoliths range from subcalcic clinopyroxenites (composed largely of unmixed prismatic subcalcic clinopyroxene megacrystals and lesser orthopyroxene megacrystals) to equant mosaic textured websterites (orthopyroxene and Ca-rich clinopyroxene ± spinel). Rare orthopyroxenite xenoliths also occur. The pyroxenite xenoliths are characterised by high 100Mg/(Mg + Fe2+) ratios (M˜ 90) and low concentrations of Ti, K, P, La, Ce and Zr. The websterites are mineralogically and chemically similar to many spinel pyroxenites occurring as layers or dykes in peridotite massifs such as those at Ronda in southern Spain and at Ariège (French Pyrénées). T / P estimates indicate crystallization temperatures of 1250–1350 °C for subcalcic clinopyroxene-orthopyroxene megacrystal pairs and 900–1000 °C for the equilibrated mosaic textured websterites and associated peridotites at pressures of 9–13 kbar. Subcalcic clinopyroxene megacrystals, websterites and orthopyroxenites have LREE-depleted chondrite-normalised REE abundances with (La/Yb)CN 〈 1 and their convex-upwards REE patterns are typical of subcalcic clinopyroxene-dominated cumulates. The pyroxenites are not residua from partially melted pyroxenite layers or dykes in mantle peridotites nor are they completely crystallized protobasaltic or protopicritic magmas. They are interpreted as high-pressure crystal segregations from basaltic magmas (probably mildly alkaline or transitional) flowing within narrow mantle conduits (the flow crystallization model of Irving, 1980). The parental magma(s) was Ti-poor (0.6–0.7% TiO2) and relatively Mg-rich (M˜ 74 − 70). Pyroxenite genesis was a two-stage process involving crystallization of tschermakitic subcalcic clinopyroxenes and orthopyroxenes  ±spinel as liquidus or near-liquidus phases at 1250–1350 °C and 9–13 kbar to yield “primary” subcalcic clinopyroxenites which then re-equilibrated at 900–1000 °C and similar pressures to produce the mosaic textured “secondary” websterites. The pyroxenites show a wide range of 143Nd/144Nd and 87Sr/86Sr values (0.513298–0.512473 and 0.702689–0.704659, respectively). Their isotopic ratios appear to have been variably modified by exchange with adjacent mantle peridotites or migrating basaltic melts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004100050280
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  • 10
    Electronic Resource
    Electronic Resource
    Shonkin Sag laccolith, Montana (1970)
    Springer
    Contributions to mineralogy and petrology 25 (1970), S. 241-269 
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    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract A variety of rock types is developed in the Shonkin Sag laccolith, with extreme compositions represented by the porphyritic pseudoleucite-bearing chilled margin, shonkinitic in composition, and by the final differentiate, chemically a nepheline syenite. During differentiation the pyroxenes changed in composition from Ca-rich varieties through aegirine-augite to acmite; there is no evidence of an immiscibility gap between Ca-rich and Na-rich pyroxenes. Olivine compositions changed from approximately Fa20 to Fa40, but in marked contrast the coexisting biotites exhibit a more extensive compositional range, from annite24 to annite100; the crystal margins of annites in the most evolved rocks are manganophyllite-rich. Titanomagnetites are TiO2-poor varieties. Arfvedsonite and melanite occur in the most evolved syenites. From mineralogical and thermodynamic data initial and final temperatures of crystallization of the various rock types have been calculated. At an estimated total vapor pressure of 310 bars, the temperature of intrusion was 985° C. Final crystallization of the laccolith took place below 700° C, and crystallization intervals for most rock types are of the order of 170° C. Over the total magmatic temperature range the activity of silica in the melt decreased from 0.13 to 0.09. Oxygen fugacity falls with temperature approximately parallel to the synthetic fayalite-magnetite-quartz oxygen buffer until olivine disappears. The crystallization of Na-rich pyroxenes does not demand an increase in the fugacity of oxygen, but rather requires that the oxygen fugacity fall less rapidly with temperature than would be the case if olivine and magnetite were present.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00399286
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