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Post-collisional ultrapotassic rocks and mantle xenoliths in the Sailipu volcanic field of Lhasa terrane, south Tibet: Petrological and geochemical constraints on mantle source and geodynamic setting

文献类型：期刊论文

作者Cheng, Zhihui1,2; Guo, Zhengfu1
刊名GONDWANA RESEARCH
出版日期2017-06-01
卷号46页码:17-42
关键词Ultrapotassic Magmatic Rocks Mantle Pyroxenite Mantle Xenoliths Indian Continental Lithosphere South Tibet
ISSN号1342-937X
DOI10.1016/j.gr.2017.02.008
文献子类Article
英文摘要Post-collisional ultrapotassic magmatic rocks (15.2-18.8 Ma), containing mantle xenoliths, are extensively distributed in the Sailipu volcanic field of the Lhasa terrane in south Tibet. They could be subdivided into highMgO and low-MgO subgroups based on their petrological and geochemical characteristics. The high-MgO subgroup has olivine-I (Fo(87-92)), phlogopite and clinopyroxene as phenocryst phases, while the low-MgO subgroup consists mainly of phlogopite, clinopyroxene and olivine-II (Fo(77-89)). These ultrapotassic magmatic rocks have high MgO (4.6-14.5 wt%), Ni (145-346 ppm), Cr (289-610 ppm) contents, and display enrichment in light rare earth element (REE) over heavy REE and enriched large ion lithophile elements (LILE) relative to high field strength elements (HFSE) with strongly negative Nb-Ta-Ti anomalies in primitive mantle-normalized trace element diagrams. They have extremely radiogenic (Sr-87/Sr-86)(i) (0.7167-0.7274) and unradiogenic (Nd-143/Nd-144)(i) (0.5118-0.5120), high (Pb-207/Pb-204)(i) (15.740-15.816) and (Pb-208/Pb-204)(i) (39.661-39.827) at a given (Pb-206/Pb-204)(i) (18.363-18.790) with high delta O-18 values (7.3-9.7 parts per thousand). Strongly linear correlations between depleted mid-ocean ridge basalt-source mantle (DMM) and the Indian continental crust (HHCS) in Sr-Nd-Pb-O isotopic diagrams indicate that the geochemical features could result from reaction between mantle peridotite and enriched components (fluids and melts) released by the eclogitized Indian continental crust (HHCS) in the mantle wedge. The high-MgO (13.7-14.5 wt%) subgroup displays higher (143Nd/144Nd) i, lower (87Sr/86Sr) i and (206Pb/204Pb) i ratios and lower delta O-18 values compared with the low-MgO (4.6-8.8 wt%) subgroup. High Ni (850-4862 ppm) contents of olivine phenocrysts and high whole-rock SiO2, NiO, low CaO contents indicate that the low-MgO ultrapotassic magmatic rocks are derived from partial melting of olivine-poor mantle pyroxenite. However, lower Ni concentrations of olivine phenocryst and lower whole-rock SiO2, NiO, higher CaO contents of the high-MgO ultrapotassic rocks may indicate their peridotite mantle source. This could be attributed to different amounts of silicate-rich components added into the mantle sources of the parental magmas in the mantle wedge caused by the northward subduction of the Indian continental lithosphere. The reaction-formed websterite xenoliths, reported for the first time in this study, are made up of anhedral and interlocking clinopyroxene (45-65 vol%) and orthopyroxene (30-50 vol%) with minor phlogopite (<3 vol%) and quartz (<2 vol%) and are suggested to be formed by silicate metasomatism of the mantle peridotite. The harzburgites, another major type of mantle xenolith in south Tibet, have a mineral assemblage of olivine (60-75 vol%), orthopyroxene (20-35 vol%), clinopyroxene (<3 vol%), phlogopite (<2 vol%) and spinel (<2 vol%) and may have experienced subduction-related metasomatism. Combined with two types of ultrapotassic magmas, we propose that compositions of mantle wedge beneath south Tibet may gradually evolve from harzburgite through lherzolite to websterite with strong metasomatism of silicate-rich components in their mantle source region. Partial melting of the enriched mantle sources could be triggered by rollback of Indian continental slab during 25-8 Ma in south Tibet.
WOS关键词INDIA-ASIA COLLISION ; ND ISOTOPIC CONSTRAINTS ; RICH MAFIC MAGMATISM ; NORTH CHINA CRATON ; BENEATH SOUTHERN ; LOWER CRUST ; CALC-ALKALINE ; CONTINENTAL SUBDUCTION ; LITHOSPHERIC MANTLE ; PLATEAU IMPLICATIONS
WOS研究方向Geology
语种英语
WOS记录号WOS:000399985000002
出版者ELSEVIER SCIENCE BV
资助机构Chinese Academy of Sciences(XDB03010600) ; National Natural Science Foundation of China (NSFC)(41572321 ; 41020124002 ; 41130314) ; Chinese Academy of Sciences(XDB03010600) ; National Natural Science Foundation of China (NSFC)(41572321 ; 41020124002 ; 41130314) ; Chinese Academy of Sciences(XDB03010600) ; National Natural Science Foundation of China (NSFC)(41572321 ; 41020124002 ; 41130314) ; Chinese Academy of Sciences(XDB03010600) ; National Natural Science Foundation of China (NSFC)(41572321 ; 41020124002 ; 41130314)
源URL[http://ir.iggcas.ac.cn/handle/132A11/52956]  
专题地质与地球物理研究所_中国科学院新生代地质与环境重点实验室
通讯作者Guo, Zhengfu
作者单位1.Chinese Acad Sci, Inst Geol & Geophys, Key Lab Cenozo Geol & Environm, POB 9825, Beijing 100029, Peoples R China
2.Univ Chinese Acad Sci, Beijing 100049, Peoples R China
推荐引用方式
GB/T 7714		 Cheng, Zhihui,Guo, Zhengfu. Post-collisional ultrapotassic rocks and mantle xenoliths in the Sailipu volcanic field of Lhasa terrane, south Tibet: Petrological and geochemical constraints on mantle source and geodynamic setting[J]. GONDWANA RESEARCH,2017,46:17-42.
APA Cheng, Zhihui,&Guo, Zhengfu.(2017).Post-collisional ultrapotassic rocks and mantle xenoliths in the Sailipu volcanic field of Lhasa terrane, south Tibet: Petrological and geochemical constraints on mantle source and geodynamic setting.GONDWANA RESEARCH,46,17-42.
MLA Cheng, Zhihui,et al."Post-collisional ultrapotassic rocks and mantle xenoliths in the Sailipu volcanic field of Lhasa terrane, south Tibet: Petrological and geochemical constraints on mantle source and geodynamic setting".GONDWANA RESEARCH 46(2017):17-42.

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来源：地质与地球物理研究所

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