Island arc-type bimodal magmatism in the eastern Tianshan Belt, Northwest China: Geochemistry, zircon U-Pb geochronology and implications for the Paleozoic crustal evolution in Central Asia

被引:109
作者
Chen, Xijie [1 ,4 ,5 ]
Shu, Liangshu [1 ]
Santosh, M. [2 ,3 ]
Zhao, Xixi [4 ,5 ]
机构
[1] Nanjing Univ, Sch Earth Sci & Engn, State Key Lab Mineral Deposits Res, Nanjing 210093, Jiangsu, Peoples R China
[2] Kochi Univ, Fac Sci, Kochi 7808520, Japan
[3] China Univ Geosci, Sch Earth Sci & Resources, Beijing 100083, Peoples R China
[4] Univ Calif Santa Cruz, Dept Earth & Planetary Sci, Santa Cruz, CA 95064 USA
[5] Univ Calif Santa Cruz, Inst Geophys & Planetary Phys, Santa Cruz, CA 95064 USA
基金
美国国家科学基金会;
关键词
Bimodal volcanic rocks; Geochemistry; Zircon U-Pb geochronology; Sr-Nd isotopes; Late Paleozoic; Eastern Tianshan Belt; ND ISOTOPIC EVIDENCE; DEPLETED-MANTLE SOURCE; TRACE-ELEMENT; NW CHINA; CALC-ALKALINE; GEODYNAMIC EVOLUTION; CONTINENTAL GROWTH; TECTONIC EVOLUTION; NORTHERN XINJIANG; VOLCANIC-ROCKS;
D O I
10.1016/j.lithos.2012.10.006
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 bimodal association of basalts and rhyolites in the Hongshankou area of the East Tianshan area (NW China) provides an important suite to investigate magma petrogenesis and tectonics evolution in a convergent margin setting. In this study we present petrological, geochemical and zircon U-Pb geochronological data from the basalts and rhyolites. Zircons from the basalts yield crystallization ages of 347.1 +/- 3.9 Ma whereas those from the rhyolites are dated as 344.4 +/- 1.9 and 345.0 +/- 2.5 Ma. The major and trace element signatures of basalts suggest high alumina basalt (HAB) as the source magma which was generated from metasomatised asthenosphere mantle. Both the mafic and felsic rocks are enriched in light rare earth elements (LREE) and large ion lithophile elements (LIE), and are depleted in high field strength elements (HFSE). Broadly homogenous Rb-Sr and Sm-Nd isotopic compositions of mafic and felsic rocks are also characteristic. The basalts display a distinct enrichment in incompatible elements and positive epsilon(Nd)(345 Ma) (from +5.87 to +8.25). We envisage a subduction-related origin to account for the LIE enrichment with arc-like melts (enriched in Th and LREE and depleted in Nb, with epsilon(Nd)(345 Ma) > + 6) produced through the partial melting of a depleted-mantle source, and the involvement of minor crustal component. The rhyolites also display high epsilon(Nd)(345 Ma) (from +635 to +8.53). Consequently, we suggest a mixing process between a source similar to mid-ocean ridge basalt (depleted end-member mantle) and arc-like magmas for the petrogenesis of the mafic rocks, whereas the rhyolites are best interpreted to have formed by fractional crystallization from the parental magma of the basalts. Several lines of evidence from elemental and isotopic geochemistry suggest a close genetic relationship between the mafic and felsic rocks in the Hongshankou bimodal suites. We propose that the essentially bimodal character of this complex reflects the features of back-arc extensional magmatism, induced by the subduction of the Junggar plate during the Late Paleozoic. (C) 2012 Elsevier B.V. All rights reserved.
引用
收藏
页码:48 / 66
页数:19
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