Citation: | CHEN Jian, WANG Xin, MENG Yuanku, XIONG Fahui, MENG Fanxue. 2024. Petrogenesis and Tectonic Implications of the Carboniferous Andesites from Bayingou in the North Tianshan Belt, Xinjiang. Northwestern Geology, 57(3): 91-112. doi: 10.12401/j.nwg.2024006 |
The Late Paleozoic volcanic rocks in the North Tianshan complex belt are the products of closure of the North Tianshan Ocean, which are important for understanding the Paleozoic evolution history of the Paleo-Asian Ocean. In this study, we present new petrological, mineralogical, geochronological and geochemical data on the Carboniferous Bayingou andesites in the North Tianshan belt, and discuss their petrogenesis and tectonic implications of the andesites. The results show that: ① the andesites belong to the calc-alkaline series that formed in a convergent continental margin setting related to the plate subduction in this study, whereas these andesites have low MgO (<3%) contents that are different from typical high-Mg andesites (>6%), whereas the andesites have high Mg# values (>45), indicating mantle materials participating in the formation of the andesites. ② In-situ LA-ICP-MS zircon U-Pb dating on the andesites of the Bayingou Formation yielded an weighted average age of (324.1±1.1) Ma (MSWD=1.5), representing the emplacement age of the andesites. The Carboniferous andesites were a mixing product of the felsic and mantle-derived melts, and the felsic melts were derived from partial melting of the mafic lower crust in the North Tianshan orogenic belt. Integrated with the previous studies and geological data, this study holds that the Bayingou Carboniferous andesites were generated in a subduction zone or arc-related environment, which further indicates that the North Tianshan Ocean was still not closed in the late Early Carboniferous.
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新疆北部地区石炭纪火山岩分布简图(a)(据夏林圻等,2002,2004;李源等,2011;熊发挥等,2011)和
北天山巴音沟地区地质简图(b)
北天山巴音沟安山岩野外分布照片
巴音沟组中酸性火山岩显微照片(a~c)和电子背散射图像(d~f)
安山岩TAS图解(a)(Le et al., 2002)(碱性与亚碱性系列分界线来自Irvine et al.,1971);安山岩的SiO2 vs.
K2O图解(Morrison, 1980)(b)
北天山巴音沟安山岩全岩主量元素哈克图解
北天山巴音沟安山岩微量元素原始地幔标准化蜘蛛网图(a)(标准化值据Sun et al., 1989)和稀土元素球粒陨石
标准化分布模式图(b)(标准化值据Boynton., 1984)
北天山巴音沟安山岩中锆石阴极发光CL图像
北天山巴音沟安山岩中锆石LA-ICP-MS U-Pb谐和图(a)和加权年龄图(b)
北天山巴音沟安山岩岩石地球化学图解 La vs. La/Yb图解(a)(矿物分离结晶模拟据Ersoy et al., 2010)、Mg# vs. SiO2 图解(b)(地壳AFC曲线据Stern et al., 1996)、主量元素成分判别图解(c)(底部据Altherr et al., 2000修)、
Y vs. Sr/Y图解(d)(据Tatsumi, 2006)
安山岩Ti/100-Zr-Y×3图解(Pearce et al., 1973)
安山岩Th/Yb-Nb/Yb图解(a)(据韩作振等,2018)和安山岩La/Yb-Th/Yb图解(b)(Pearce et al., 1981)