Intra-continental boninite-series volcanic rocks from the Bangong-Nujiang Suture Zone, Central Tibet

被引:4
|
作者
Zhao, Bin [1 ,2 ]
Shi, Ren-Deng [1 ,3 ]
Zou, Hai-Bo [4 ]
Chen, Sheng-Sheng [1 ]
Huang, Qi-Shuai [1 ]
Sun, Ya-Li [1 ,3 ]
Yang, Jing-Sui [5 ]
机构
[1] Chinese Acad Sci, Inst Tibetan Plateau Res, Key Lab Continental Collis & Plateau Uplift, Beijing 100101, Peoples R China
[2] Univ Chinese Acad Sci, Beijing 100049, Peoples R China
[3] Chinese Acad Sci, Ctr Excellence Tibetan Plateau Earth Sci, Beijing 100101, Peoples R China
[4] Auburn Univ, Dept Geosci, Auburn, AL 36849 USA
[5] Nanjing Univ, Sch Earth Sci & Engn, Nanjing 210023, Peoples R China
基金
中国国家自然科学基金;
关键词
Boninite-series volcanic rocks; Intra-oceanic subduction; Lithospheric delamination; Bangong-Nujiang Suture Zone; Tibetan Plateau; PLASMA-MASS SPECTROMETRY; HIGH-MG ANDESITES; TRACE-ELEMENT; SUBDUCTION INITIATION; ISOTOPIC COMPOSITION; GEOCHEMICAL EVIDENCE; TECTONIC EVOLUTION; OPHIOLITE MELANGE; OCEANIC-CRUST; MANTLE;
D O I
10.1016/j.lithos.2021.106024
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
The boninitic volcanic rocks from Rutog, western Bangong-Nujiang Suture Zone (BNSZ), are characterized by high MgO, SiO2 but low TiO2 contents and interpreted as the products of intra-oceanic subduction in earlier studies. Recently, we discovered new breccia-like boninitic volcanic rocks (mainly trachyandesite and trachyte) that overlie the Rutog ophiolitic peridotites in BNSZ. These volcanic rocks not only show typical boninitic petro-graphical features of porphyritic texture in which euhedral augite phenocrysts (ca. 5 vol%) are embedded in fine-grained groundmass composed of pyroxene, plagioclase, quartz and minor glass, but also display strong boninitic geochemical affinities with high Mg# (61.59?67.90), Al2O3/TiO2 (40.31?55.97) ratios and low TiO2 (0.26?0.35 wt%) contents. In addition, their rare earth elemental patterns show a slight right-dip pattern with (La/Gd)N values of-1.28 and (Gd/Yb)N values of-1.31. Given the evolutionary trend from magnesium-rich inter-mediate to acid series, the boninite-series are therefore used to describe the vlocanic rocks. Zircon U-Pb isotopic dating on these boninite-series volcanic rocks yielded an age of ca. 79.3 +/- 2.0 Ma, after the closure of the Bangong-Nujiang Tethyan Ocean (BNTO) that occurred before 96 Ma. The newly recognized boninite-series vol-canic rocks probably formed more than 20 Ma after the latest regional magmatism related to subduction process and thus the subduction setting is not suitable for these boninite-series volcanic rocks. The enrichment in com-patible elements and depletion in high field elements indicate the Rutog boninite-series originated from a se-verely depleted mantle while several lines of evidence (e.g., the enrichment in light rare earth elements, large iron lithophile elements) imply that the mantle source has been modified by continental crust. Given the wide-spread Cretaceous high Sr/Y magmatic rocks within BNSZ, the Rutog boninite-series rocks may provide an exam-ple of the crust-mantle interaction as a result of the delamination in a partially thickened and cratonized convergent margin during the late Cretaceous within BNSZ, central Tibetan Plateau. ? 2021 Elsevier B.V. All rights reserved.
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页数:16
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