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Geochronology and Petrogenesis of Late Carboniferous to Early Permian Basalts in the Central Lhasa Subterrane, Southern Tibet: Implications for the Evolution of the Sumdo Paleo-Tethys Ocean

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Acta Geologica Sinica(English Edition) 2024年第4期98卷 955-968页

作者： MA Wang LIU Yingchao YANG Zhusen jan-marten huizenga LI Zhenqing YUE Longlong ZHAO Sibo School of Earth Sciences and Resources China University of GeosciencesBeijing 100083China Institute of Geology Sinoprobe LaboratoryChinese Academy of Geological SciencesBeijing 100037China MLR Key Laboratory of Metallogeny and Mineral Assessment Institute of Mineral ResourcesChinese Academy of Geological SciencesBeijing 100037China Faculty of Environmental Sciences and Natural Resource Management Norwegian University of Life SciencesNO-1432ÅsNorway Economic Geology Research Centre(EGRU) College of Science and EngineeringJames Cook UniversityTownsvilleQueensland 4811Australia Department of Geology University of JohannesburgAuckland Park 2006South Africa

Basalts from the Late Carboniferous to Early Permian are extensively developed in the central Lhasa subterrane, southern Tibet. Studying the petrogenesis of these rocks may have implications for the late Paleozoic arc magmatism along the central Lhasa subterrane uncovering more of the evolution of the Sumdo Paleo-Tethys Ocean and its dynamic mechanism. Basalt samples from the Luobadui Formation in the Leqingla area, NW of Linzhou City in the central Lhasa subterrane, southern Tibet exhibit arc-like geochemical signatures in a subduction-zone tectonic setting characterized by high Al_(2)O_(3) and low TiO_(2) contents, fractionated REE patterns with low Nb/La ratios and high LREE concentrations, and negative HFSE anomalies. Based on their higher Th/Ce, Nb/Zr, and lower Ba/Th, Pb/Nd ratios, slightly negative to positive ε_(Nd)(t) values, and the relatively high Sr-Pb isotopic compositions, these samples were probably derived from partial melting of a depleted mantle source of garnet + spinel lherzolite, metasomatized by subducted sediments around 297 Ma. Modeling of the trace elements indicates that these basalts experienced fractional crystallization of olivine, clinopyroxene and minor plagioclase during magma ascent and eruption. It is proposed that these Late Carboniferous–Early Permian basalts are associated with the northward subduction of the Sumdo Paleo-Tethys Ocean seafloor along the southern margin of the central Lhasa subterrane.

关键词： geochemistry northward subduction Sumdo Paleo-Tethys Ocean Lhasa terrane Tibet

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Fluid-rock interaction in retrograde granulites of the Southern Marginal Zone,Limpopo high grade terrain,South Africa

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Geoscience Frontiers 2014年第5期5卷 673-682页

作者： jan marten huizenga Dirk van Reenen Jacques L.R.Touret Unit of Environmental Sciences and Management North-West UniversityPrivate Bag X60012520South Africa Economic Geology Research Institute(EGRU) School of Earth and Environmental SciencesJames Cook UniversityTownsvilleQLD 4811Australia Department of Geology University of JohannesburgJohannesburgSouth Africa Institut de Mineralogie.de Physique des Materiaux et de Cosmochimie(IMPMC) Sorbonne Universites UPMC Univ Paris 06UMR CNRS 7590 Museum National d'Histoire Naturelle.IRD UMR 206.4 Place Jussieu.F-75005

Fluid infiltration into retrograde granulites of the Southern Marginal Zone （Limpopo high grade terrain） is exemplified by hydration reactions, shear zone hosted metasomatism, and lode gold mineralisation. Hydration reactions include the breakdown of cordierite and orthopyroxene to gedrite ＋ kyanite, and anthophyllite, respectively. Metamorphic petrology, fluid inclusions, and field data indicate that a low H2O-activity carbon-saturated CO2-rich and a saline aqueous fluid infiltrated the Southern Marginal Zone during exhumation. The formation of anthophyllite after orthopyroxene established a regional retrograde anthophyllite-in isograd and occurred at P-Tconditions of -6 kbar and 610 ℃, which fixes the minimum mole fraction of H20 in the CO2-rich fluid phase at ~ 0.1. The maximum H20 mole fraction is fixed by the lower temperature limit （~800 ℃） for partial melting at -0.3. C-O-H fluid calculations show that the CO2-rich fluid had an oxygen fugacity that was 0.6 log10 units higher than that of the fayalite-magnetite- quartz buffer and that the CO2/（CO2＋CH4） mole ratio of this fluid was 1. The presence of dominantly relatively low density CO2-rich fluid inclusions in the hydrated granulites indicates that the fluid pressure was less than the lithostatic pressure. This can be explained by strike slip faulting and/or an increase of the rock permeability caused by hydration reactions.

关键词： GranuliteFluidLimpopoRetrogradeSouthern Marginal Zone

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Charnockite microstructures:From magmatic to metamorphic

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Geoscience Frontiers 2012年第6期3卷 745-753页

作者： Jacques L.R.Touret jan marten huizenga Musee de Mineralogie MINES ParisTech75272 Paris Cedex 06France Department of Geology.School of Environmental Sciences and Development North-West UniversityPrivate Bag X6001Potchefstroom 2520South Africa

Charnockites sensu lato （charnockite-enderbite series） are lower crustal felsic rocks typically characterised by the presence of anhydrous minerals including orthopyroxene and garnet. They either represent dry （H2O-poor） felsic magmas that are emplaced in the lower crust or granitic intrusions that have been dehydrated during a subsequent granulite facies metamorphic event. In the first case, post- magmatic high-temperature recrystallisation may result in widespread metamorphic granulite microstruc- tures, superimposed or replacing the magmatic microstructures. Despite recrystallisation, magmatic remnants may still be found, notably in the form of melt-related microstructures such as melt inclusions. For both magmatic charnockites and dehydrated granites, subsequent fluid-mineral interaction at inter- grain boundaries during retrogradation are documented by microstructures including K-feldspar micro- veins and myrmekites. They indicate that a large quantity of low-H2O activity salt-rich brines, were present （together with CO2 under immiscible conditions） in the lower crust.

关键词： Charnockite Petrology Microstructure Melt inclusions

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