Citation: | LI Lijuan, ZHANG Tao, LI Qiang, YUN Jie, HE Li, CHENG Xueqin, ZHAO Liying. 2024. Petrogenesis and Tectonic Implications of Carboniferous Granites and Its Dark Enclaves in the Western Awulale Mountain, Western Tianshan. Northwestern Geology, 57(3): 73-90. doi: 10.12401/j.nwg.2024011 |
The petrogenesis and dynamic background of the magmatic rocks in the West Tianshan Mountains are of great significance to reveal the tectonic evolution history of the restoration area. In this paper, the granite and its dark enclaves in the northwestern area of Kunes Zhongyangchang in the western Awulale Mountain were selected for petrology and zircon U-Pb chronology and petrogeochemical analysis. The results show that the dark enclaves are fine-grained diorite, with K2O=0.93~2.50, K2O/Na2O=0.20~0.21, A/CNK=0.83~0.87 and σ=2.33~3.02, which are quasi-aluminous calc-alkaline rock series. Host granites belong to I type granites with K2O=2.92~3.48, K2O/Na2O=0.60~0.79, Ritman index σ=1.87~2.17, and A/CNK =1.01~1.04, which are weakly peraluminous calc-alkaline rock series. Both of them are enriched in large ion lithophile elements (LILE, e.g. Rb、Ba、Pb) and depleted in high field strength elements (HSFE, e.g. Nb, Ta, Ti), The total amount of rare earth elements is low, accompanied by the relative enrichment of light rare earth elements, and the relative loss of heavy rare earth element. The diorite enclaves have no significant Eu and Sr anomalies, while the granites have obvious negative Eu anomalies and strong loss of Sr, P and Ti elements. Zircon U-Pb dating shows that the formation age of granite is (320.0±2.7) Ma, belonging to the early Late Carboniferous. The diagenetic age of the diorite enclaves is (344.5±1.4) Ma, belonging to the Early Carboniferous. The type of diorite enclaves is xenolith, which were captured during the rising of the host granitic magma. The geochemical and chronological characteristics of the rocks reveal that they have different petrogenesis. The dioritic enclaves were formed during the northern Tianshan Ocean subduction southward, and the granite intrusion was located in the post-collision extension environment, which was formed due to the upwelling of the asthenosphere, leading to the partial melting of the lower crust. Based on regional geological data, it is likely that the early Carboniferous to late Carboniferous is an important stage of tectonic system transformation in the western Tianshan Mountain, that is, the tectonic environment transformed from compression to extension.
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doi: 10.1029/2019TC005822 |
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中国西天山地质简图(a据Long et al.,2011修)和研究区地质简图(b)
寄主花岗岩及闪长质包体野外照片及正交偏光显微照片
花岗岩(13XY-24)和闪长质包体(13XY-12)锆石阴极发光图
闪长质包体(a、b)和寄主花岗岩(c、d)锆石U-Pb谐和图及加权平均年龄图
花岗岩和闪长质包体TAS图解(a据 Middlemost,1994)和K2O-SiO2图解
(b据Peccerillo et al.,1976,虚线据Middlemost,1985)
花岗岩和捕掳体稀土元素球粒陨石标准化配图(a)和微量元素原始地幔标准化蛛网图(b)
花岗岩FeOT/MgO-
研究区闪长质包体Th/Yb-Ta/Yb(a据Pearce,1982)和La/Yb-Th(b据Bailey,1981)图解
花岗岩和包体R1-R2(a据Batchelor et al.,1985)和Rb-Yb+Nb(b据Pearce,1996)构造环境判别图解