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The origin of shoshonites: new insights from the Tertiary high-potassium intrusions of eastern Tibet
Campbell, IH; Stepanov, AS; Liang, HY; Allen, CM; Norman, MD; Zhang, YQ; Xie, YW; ian.campbell@anu.edu.au
2014
Source PublicationCONTRIBUTIONS TO MINERALOGY AND PETROLOGY
ISSN0010-7999
Volume167Issue:3Pages:-983
AbstractThe shoshonitic intrusions of eastern Tibet, which range in age from 33 to 41 Ma and in composition from ultramafic (SiO2 = 42 %) to felsic (SiO2 = 74 %), were produced during the collision of India with Eurasia. The mafic and ultramafic members of the suite are characterized by phenocrysts of phlogopite, olivine and clinopyroxene, low SiO2, high MgO and Mg/Fe ratios, and olivine forsterite contents of Fo(87) to Fo(93), indicative of equilibrium with mantle olivine and orthopyroxene. Direct melting of themantle, on the other hand, could not have produced the felsic members. They have a phenocryst assemblage of plagioclase, amphibole and quartz, high SiO2 and lowMgO, with Mg/Fe ratios well below the values expected for a melt in equilibrium with the mantle. Furthermore, the lack of decrease in Cr with increasing SiO2 and decreasing MgO from ultramafic to felsic rocks precludes the possibility that the felsic members were derived by fractional crystallization from the mafic members. Similarly, magma mixing, crustal contamination and crystal accumulation can be excluded as important processes. Yet all members of the suite share similar incompatible element and radiogenic isotope ratios, which suggests a common origin and source. We propose that melting for all members of the shoshonite suite was initiated in continental crust that was thrust into the upper mantle at various points along the transpressional Red RiverAilao Shan-Batang-Lijiang fault system. The melt formed by high-degree, fluid-absent melting reactions at high-T and highP and at the expense of biotite and phengite. Themelts acquired their high concentrations of incompatible elements as a consequence of the complete dissolution of pre-existing accessory minerals. The melts produced were quartz-saturated and reacted with the overlying mantle to produce garnet and pyroxene during their ascent. The felsic magmas reacted little with the adjacent mantle and preserved the essential features of their original chemistry, including their high SiO2, low Ni, Cr and MgO contents, and low Mg/Fe ratio, whereas the mafic and ultramaficmagmas are the result of extensive reaction with the mantle. Although the mafic magmas preserved the incompatible element and radiogenic isotope ratios of their crustal source, buffering by olivine and orthopyroxene extensively modified their MgO, Ni, Cr, SiO2 contents and Mg/Fe ratio to values dictated by equilibrium with the mantle.
Department[Campbell, Ian H. ; Stepanov, Aleksandr S. ; Liang, Hua-Ying ; Allen, Charlotte M. ; Norman, Marc D.] Australian Natl Univ, Res Sch Earth Sci, Canberra, ACT 0200, Australia ; [Liang, Hua-Ying] Chinese Acad Sci, Guangzhou Inst Geochem, Key Lab Mineral & Metallogeny, Guangzhou 510640, Guangdong, Peoples R China ; [Zhang, Yu-Qiang ; Xie, Ying-Wen] Chinese Acad Sci, Lab Marginal Sea Geol, Guangzhou Inst Geochem, South China Sea Inst Oceanol, Guangzhou 510640, Guangdong, Peoples R China
KeywordShoshonite High-potassium Magmas High-potassium Intrusions Eastern Tibet Red River-ailao Shan-batang-lijiang Fault System
Subject AreaGeochemistry & Geophysics ; Mineralogy
Funding OrganizationChinese Academy of Sciences [XDB03010302]; China Scholarship Council; Chinese NSF [41121002, 41272099, 41172080] ; Chinese Academy of Sciences [XDB03010302]; China Scholarship Council; Chinese NSF [41121002, 41272099, 41172080] ; Chinese Academy of Sciences [XDB03010302]; China Scholarship Council; Chinese NSF [41121002, 41272099, 41172080] ; Chinese Academy of Sciences [XDB03010302]; China Scholarship Council; Chinese NSF [41121002, 41272099, 41172080]
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Indexed Bysci
Funding Project海洋地质
Funding OrganizationChinese Academy of Sciences [XDB03010302]; China Scholarship Council; Chinese NSF [41121002, 41272099, 41172080] ; Chinese Academy of Sciences [XDB03010302]; China Scholarship Council; Chinese NSF [41121002, 41272099, 41172080] ; Chinese Academy of Sciences [XDB03010302]; China Scholarship Council; Chinese NSF [41121002, 41272099, 41172080] ; Chinese Academy of Sciences [XDB03010302]; China Scholarship Council; Chinese NSF [41121002, 41272099, 41172080]
WOS IDWOS:000332585700006
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Document Type期刊论文
Identifierhttp://ir.scsio.ac.cn/handle/344004/10639
Collection中科院边缘海地质重点实验室
Corresponding Authorian.campbell@anu.edu.au
Recommended Citation
GB/T 7714
Campbell, IH,Stepanov, AS,Liang, HY,et al. The origin of shoshonites: new insights from the Tertiary high-potassium intrusions of eastern Tibet[J]. CONTRIBUTIONS TO MINERALOGY AND PETROLOGY,2014,167(3):-983.
APA Campbell, IH.,Stepanov, AS.,Liang, HY.,Allen, CM.,Norman, MD.,...&ian.campbell@anu.edu.au.(2014).The origin of shoshonites: new insights from the Tertiary high-potassium intrusions of eastern Tibet.CONTRIBUTIONS TO MINERALOGY AND PETROLOGY,167(3),-983.
MLA Campbell, IH,et al."The origin of shoshonites: new insights from the Tertiary high-potassium intrusions of eastern Tibet".CONTRIBUTIONS TO MINERALOGY AND PETROLOGY 167.3(2014):-983.
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