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  • 1
    Electronic Resource
    Electronic Resource
    Pro- and retrograde P–T evolution of granulites of the Beit Bridge Complex (Limpopo Belt, South Africa): constraints from quantitative phase diagrams and geotectonic implications (2004)
    Oxford, UK : Blackwell Science Inc
    Journal of metamorphic geology 22 (2004), S. 0 
    Details
    ISSN: 1525-1314
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Interpretations based on quantitative phase diagrams in the system CaO–Na2O–K2O–TiO2–MnO–FeO–MgO–Al2O3–SiO2–H2O indicate that mineral assemblages, zonations and microstructures observed in migmatitic rocks from the Beit Bridge Complex (Messina area, Limpopo Belt) formed along a clockwise P–T path. That path displays a prograde P–T increase from 600 °C/7.0 kbar to 780 °C/9–10 kbar (pressure peak) and 820 °C/8 kbar (thermal peak), followed by a P–T decrease to 600 °C/4 kbar. The data used to construct the P–T path were derived from three samples of migmatitic gneiss from a restricted area, each of which has a distinct bulk composition: (1) a K, Al-rich garnet–biotite–cordierite–sillimanite–K-feldspar–plagioclase–quartz–graphite gneiss (2) a K-poor, Al-rich garnet–biotite–staurolite–cordierite–kyanite–sillimanite–plagioclase–quartz–rutile gneiss, and (3) a K, Al-poor, Fe-rich garnet–orthopyroxene–biotite–chlorite–plagioclase–quartz–rutile–ilmenite gneiss. Preservation of continuous prograde garnet growth zonation demonstrates that the pro- and retrograde P–T evolution of the gneisses must have been rapid, occurring during a single orogenic cycle. These petrological findings in combination with existing geochronological and structural data show that granulite facies metamorphism of the Beit Bridge metasedimentary rocks resulted from an orogenic event during the Palaeoproterozoic (c. 2.0 Ga), caused by oblique collision between the Kaapvaal and Zimbabwe Cratons. Abbreviations follow Kretz (1983).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1525-1314.2004.00501.x
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  • 2
    Electronic Resource
    Electronic Resource
    P–T path of high-pressure/low-temperature rocks and tectonic implications in the western Tianshan Mountains, NW China (1999)
    Oxford, UK : Blackwell Science Inc
    Journal of metamorphic geology 17 (1999), S. 0 
    Details
    ISSN: 1525-1314
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The Chinese western Tianshan high-pressure/low-temperature (HP–LT) metamorphic belt, which extends for about 200 km along the South Central Tianshan suture zone, is composed of mainly metabasic blueschists, eclogites and greenschist facies rocks. The metabasic blueschists occur as small discrete blocks, lenses, bands, laminae or thick beds in meta-sedimentary greenschist facies country rocks. Eclogites are intercalated within blueschist layers as lenses, laminae, thick beds or large massive blocks (up to 2 km2 in plan view). Metabasic blueschists consist of mainly garnet, sodic amphibole, phengite, paragonite, clinozoisite, epidote, chlorite, albite, accessory titanite and ilmenite. Eclogites are predominantly composed of garnet, omphacite, sodic–calcic amphibole, clinozoisite, phengite, paragonite, quartz with accessory minerals such as rutile, titanite, ilmenite, calcite and apatite. Garnet in eclogite has a composition of 53–79 mol% almandine, 8.5–30 mol% grossular, 5–24 mol% pyrope and 0.6–13 mol% spessartine. Garnet in blueschists shows similar composition. Sodic amphiboles include glaucophane, ferro-glaucophane and crossite, whereas the sodic–calcic amphiboles mainly comprise barroisite and winchite. The jadeite content of omphacite varies from 35–54 mol%. Peak eclogite facies temperatures are estimated as 480–580 °C for a pressure range of 14–21 kbar. The conditions of pre-peak, epidote–blueschist facies metamorphism are estimated to be 350–450 °C and 8–12 kbar. All rock types have experienced a clockwise P–T  path through pre-peak lawsonite/epidote-blueschist to eclogite facies conditions. The retrograde part of the P–T  path is represented by the transition of epidote-blueschist to greenschist facies conditions. The P–T  path indicates that the high-pressure rocks formed in a B-type subduction zone along the northern margin of the Palaeozoic South Tianshan ocean between the Tarim and Yili-central Tianshan plates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1525-1314.1999.00219.x
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  • 3
    Electronic Resource
    Electronic Resource
    Reaction textures and fluid behaviour in very high pressure calc-silicate rocks of the Münchberg gneiss complex, Bavaria, Germany (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    Details
    ISSN: 1525-1314
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Calc-silicate rocks occur as elliptical bands and boudins intimately interlayered with eclogites and high-pressure gneisses in the Münchberg gneiss complex of NE Bavaria. Core assemblages of the boudins consist of grossular-rich garnet, diopside, quartz, zoisite, clinozoisite, calcite, rutile and titanite. The polygonal granoblastic texture commonly displays mineral relics and reaction textures such as post kinematic grossular-rich garnet coronas. Reactions between these mineral phases have been modelled in the CaO-Al2O3-SiO2-CO2-H2O system with an internally consistent thermodynamic data base. High-pressure metamorphism in the calc-silicate rocks has been estimated at a minimum pressure of 31 kbar at a temperature of 630d̀ C with XH2, O ≥ 0.03. Small volumes of a CO2-N2-rich fluid whose composition was buffered on a local scale were present at peak-metamorphic conditions. The P-T conditions for the onset of the amphibolite facies overprint are about 10 kbar at the same temperature. XCo2 of the H2O-rich fluid phase is regarded to have been 〈0.03 during amphibolite facies conditions. These P-T estimates are interpreted as representing different stages of recrystallization during isothermal decompression. The presence of multiple generations of mineral phases and the preservation of very high-pressure relics in single thin sections preclude pervasive post-peak metamorphic fluid flow as a cause of a re-equilibration within the calc-silicates. The preservation of eclogite facies, very high-pressure relics as well as amphibolite facies reactions textures in the presence of a fluid phase is in agreement with fast, tectonically driven unroofing of these rocks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1525-1314.1994.tb00056.x
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  • 4
    Electronic Resource
    Electronic Resource
    P–T evolution of glaucophane–omphacite bearing HP–LT rocks in the western Tianshan Orogen, NW China:new evidence for ‘Alpine-type’ tectonics (2002)
    Oxford, UK : Blackwell Science, Ltd
    Journal of metamorphic geology 20 (2002), S. 0 
    Details
    ISSN: 1525-1314
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The late Palaeozoic western Tianshan high-pressure /low-temperature belt extends for about 200 km along the south-central Tianshan suture zone and is composed mainly of blueschist, eclogite and epidote amphibolite/greenschist facies rocks. P–T conditions of mafic garnet omphacite and garnet–omphacite blueschist, which are interlayered with eclogite, were investigated in order to establish an exhumation path for these high-pressure rocks. Maximum pressure conditions are represented by the assemblage garnet–omphacite–paragonite–phengite–glaucophane–quartz–rutile. Estimated maximum pressures range between 18 and 21 kbar at temperatures between 490 and 570 °C. Decompression caused the destabilization of omphacite, garnet and glaucophane to albite, Ca-amphibole and chlorite. The post-eclogite facies metamorphic conditions between 9 and 14 kbar at 480–570 °C suggest an almost isothermal decompression from eclogite to epidote–amphibolite facies conditions. Prograde growth zoning and mineral inclusions in garnet as well as post-eclogite facies conditions are evidence for a clockwise P–T path. Analysis of phase diagrams constrains the P–T path to more or less isothermal cooling which is well corroborated by the results of geothermobarometry and mineral textures. This implies that the high-pressure rocks from the western Tianshan Orogen formed in a tectonic regime similar to ‘Alpine-type’ tectonics. This contradicts previous models which favour ‘Franciscan-type’ tectonics for the southern Tianshan high-pressure rocks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1525-1314.2002.00347.x
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  • 5
    Electronic Resource
    Electronic Resource
    Phase relationships in grunerite–garnet-bearing amphibolites in the system CFMASH, with applications to metamorphic rocks from the Central Zone of the Limpopo Belt, South Africa (2005)
    Oxford, UK : Blackwell Science Inc
    Journal of metamorphic geology 23 (2005), S. 0 
    Details
    ISSN: 1525-1314
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: A petrogenetic grid in the model system CaO–FeO–MgO–Al2O3–SiO2–H2O is presented, illustrating the phase relationships among the minerals grunerite, hornblende, garnet, clinopyroxene, chlorite, olivine, anorthite, zoisite and aluminosilicates, with quartz and H2O in excess. The grid was calculated with the computer software thermocalc, using an upgraded version of the internally consistent thermodynamic dataset HP98 and non-ideal mixing activity models for all solid solutions. From this grid, quantitative phase diagrams (P–T pseudosections) are derived and employed to infer a P–T path for grunerite–garnet-bearing amphibolites from the Endora Klippe, part of the Venetia Klippen Complex within the Central Zone of the Limpopo Belt. Agreement between calculated and observed mineral assemblages and garnet zonation indicates that this part of the Central Zone underwent a prograde temperature and pressure increase from c. 540 °C/4.5 kbar to 650 °C/6.5 kbar, followed by a post-peak metamorphic pressure decrease. The inferred P–T path supports a geotectonic model suggesting that the area surrounding the Venetia kimberlite pipes represents the amphibolite-facies roof zone of migmatitic gneisses and granulites that occur widely within the Central Zone. In addition, the P–T path conforms to an interpretation that the Proterozoic evolution of the Central Zone was controlled by horizontal tectonics, causing stacking and differential heating at c. 2.0 Ga.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1525-1314.2005.00554.x
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  • 6
    Electronic Resource
    Electronic Resource
    Comment on the paper by Schmidt Mumm et al. High CO2 content of fluid inclusions in gold mineralisations in the Ashanti Belt, Ghana: a new category of ore forming fluids? (Mineralium Deposita 32: 107–118, 1997) (1998)
    Springer
    Mineralium deposita 33 (1998), S. 317-319 
    Details
    ISSN: 1432-1866
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001260050151
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  • 7
    Electronic Resource
    Electronic Resource
    Hydrothermally altered peraluminous Archaean granites as a provenance model for Witwatersrand sediments (1987)
    Springer
    Mineralium deposita 22 (1987), S. 227-235 
    Details
    ISSN: 1432-1866
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Hydrothermal alteration of peraluminous granitic rocks, occurring at Varkenskraal, northwest of the Witwatersrand Basin, consists of two major styles. The first style, pervasive in nature, is represented by two stages: i) A propylitic alteration and ii) A disseminated sericitization. Both alteration stages were accompanied by a deposition of disseminated sulphides. The second style is represented by a vein related alteration in four stages including potassium feldspar, minor carbonate and minor sulphide mineralization. Nodules of uraniferous carbonaceous matter and small amounts of particulate gold could possibly be associated with either one or both styles. Hydrothermally altered rocks of similar nature have been observed in a number of other localities close to the Witwatersrand Basin. Their abundance, large volumes and low-grade, disseminated pyrite/gold mineralization indicate that rocks of this type could have been the provenance of the Witwatersrand gold-bearing sediments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00206614
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  • 8
    Electronic Resource
    Electronic Resource
    The geology and geochronology of the Annandagstoppane granite, Western Dronning Maud Land, Antarctica (1987)
    Springer
    Contributions to mineralogy and petrology 97 (1987), S. 488-496 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The Annandagstoppane Granite is exposed at three nunataks in Western Dronning Maud Land, Antarctica. It comprises medium- to coarse-grained granite crosscut by veins of pegmatite and graphic granite and has many S-type characteristics such as containing normative corundum greater than 1.1%, molecular Al2O3/(CaO+K2O+Na2O) greater than 1.1 and very little zircon. Hydrothermal alteration in the Granite is variably developed and has affected only certain minerals in any phase. R-Sr and Pb whole rock and mineral isotopic data suggest: 1) that Sr isotopes within it were nearly homogenized on a whole rock scale about 2823 Ma ago by this hydrothermal alteration; 2) that the Pb isotopic system was also disturbed at that time, and 3) that the Granite may have been was emplaced sometime during the interval 3115 Ma to 2945 Ma ago. The Granite was probably intruded by the Annandagstoppane Gabbro about 1200 Ma ago, resetting the Rb-Sr system in biotite. The Annandagstoppane Granite may form part of a basement complex to the Proterozoic sedimentary, volcanic and mafic igneous rocks exposed to the east in the Ahlmannryggen and the Borgmassivet. Its chemical composition and geologic history appears to be unique in Antarctica and in the Kaapvaal Craton of Southern Africa, consistent with the possibility that the Annandagstoppane Granite is part of a crustal fragment that joined Antarctica relatively late in the history of that continent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00375326
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  • 9
    Electronic Resource
    Electronic Resource
    P-T evolution and fluid inclusion characteristics of retrograded eclogites, Münchberg Gneiss Complex, Germany (1989)
    Springer
    Contributions to mineralogy and petrology 102 (1989), S. 221-229 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Kyanite eclogites occur as part of the Münchberger nappe pile in NE-Bavaria, West Germany. Eclogites are overprinted by subsequent amphibolite facies metamorphism. The preservation of primary eclogitic textures as well as symplectitic textures are indicative of rapid decompression. Eclogite formation is estimated to have occurred under conditions of high H2O-activities at pressures between 20 and 26 kbar and temperatures ranging between 590 and 660° C, as is shown by the coexistence of omphacite (Jd 50), kyanite, zoisite and quartz. Minimum pressure estimates, independent of the water activity, range between 9 and 16 kbar at the relevant temperatures. Detailed studies of fluid inclusion reveal two predominant groups of aqueous-brine inclusions: high salinity (14–17 wt% NaCl equiv.) and low salinity (0–8 wt% NaCl equiv.) inclusions. Fluid compositions of both groups of inclusions yield isochores passing close to the estimated amphibolite facies PT-field. The compositions of these fluids are in good agreement with fluid compositions considered from mineral equilibria. None of the fluid inclusions has densities appropriate for eclogite facies metamorphism, but probably reflect later amphibolite facies metamorphism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00375342
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  • 10
    Electronic Resource
    Electronic Resource
    Fluid influence on mineral reactions in ultrahigh-pressure granulites: a case study in the Śnieżnik Mts. (West Sudetes, Poland) (1999)
    Springer
    Contributions to mineralogy and petrology 136 (1999), S. 358-373 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Small tectonic slices of undeformed eclogites and ultrahigh-pressure granulites occur in three tectonic units of the Śnieżnik Mts. (SW Poland). Ultrahigh-pressure granulite/eclogite transitions with peak metamorphic conditions between 21 and 28 kbar at 800 to 1000 °C occur only in the Złote unit. Conventional U-Pb multigrain analyses of zircons from a mafic granulite provided 207Pb/206Pb ages between 360 to 369 Ma which are interpreted to approximate timing of original crystallisation from a melt. Diffusion kinetics and the restricted availability of a fluid phase mainly controlled the conversion from granulite to eclogite, although some bulk-chemical differences were also recognised. The ultrahigh-pressure granulites from the Złote unit exclusively contain H2O-rich inclusions with variable salinities which distinguishes them from high-temperature (HT)-granulites world-wide. This is also in contrast to the fluid regime (H2O-N2-CO2) recognised in the lower-temperature eclogites (600–800 °C) from the closely associated Międzygórze and Śnieżnik units. The variation in fluid composition between the lower-temperature eclogites and ultrahigh-pressure granulites on the one hand and ultrahigh-pressure granulites and HT-granulites on the other hand probably indicates contrasting P-T-t paths as a result of different tectonic environments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004100050544
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