Petrogenesis of rhyolite at Kalatage in the Eastern Tianshan, Northwest China: Evidences from geochemistry, zircon U-Pb geochronology, and Hf isotopes
Petrogenesis of rhyolite at Kalatage in the Eastern Tianshan, Northwest China: Evidences from geochemistry, zircon U-Pb geochronology, and Hf isotopes
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东天山卡拉塔格流纹岩岩石成因：地球化学、锆石U-Pb年代学和Hf同位素证据
DOI：
10.1002/gj.3175
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发表时间：
2018
影响因子：
1.8
通讯作者：
Tan Xijuan
中科院分区：
文献类型：
--
作者：
Sun Xiaohui;Luan Yan;Tang Haoshu;Tan Xijuan
中亚造山带是世界范围内显生宙新生代地壳生长最重要的场所之一，而位于中亚造山带南部的中国西北东天山是揭示增生过程和大陆生长的关键地区之一。对东天山哈里克-大南湖弧中部卡拉塔格地区上石炭统岐山组流纹岩进行了锆石U-Pb年代学、Hf同位素和全岩地球化学分析，以探讨其岩石成因和地球动力学环境。通过激光烧蚀电感耦合质谱（LA-ICP-MS）获得的锆石U-Pb年龄表明流纹岩的锆石结晶年龄为299.1±2.1Ma。流纹岩分为弱碱性和高K钙碱性系列，A/CNK值主要低于1.10。稀土元素分布呈右倾曲线，Eu负异常，微量元素蜘蛛网图显示Nb、Ta和Eu的贫化，这与岛弧钙碱性岩浆经历分异结晶的地球化学特征一致。原位锆石 Hf 同位素分析得出正初始 εHf(t) 值，范围为 8.0 至 11.9，两阶段 Hf 同位素地壳模型年龄 (TDMC) 为 554 至 807 Ma。这表明流纹岩是新生地壳重熔的产物。流纹岩的地球化学数据表明它们可能是在超俯冲带环境中生成的。推测北天山洋壳在上石炭世晚期向北俯冲到Harlik-Dananhu弧之下，流纹岩源自新生地壳的重熔并在超俯冲带环境中生成。
The Central Asian Orogenic Belt was one of the most important sites for juvenile crustal growth during the Phanerozoic worldwide, and Eastern Tianshan, Northwest China, located in southern Central Asian Orogenic Belt, is one of the key areas for unravelling the accretionary processes and continental growth. Zircon U–Pb geochronological, Hf isotopic, and whole‐rock geochemical analyses are reported for the Upper Carboniferous Qishan Formation rhyolites from the Kalatage area in the middle of the Harlik–Dananhu arc, Eastern Tianshan, to investigate its petrogenesis and geodynamic setting. Zircon U–Pb ages obtained by laser‐ablation inductively coupled mass spectrometry (LA‐ICP‐MS) indicated that zircon crystallization age of the rhyolite was 299.1 ± 2.1 Ma. The rhyolites are classified as subalkaline and high‐K calc‐alkaline series with A/CNK values mainly lower than 1.10. The REE patterns exhibit right inclined curves with negative Eu anomalies, and the trace element spider diagrams show depletions in Nb, Ta, and Eu, which is consistent with the geochemical characteristics of the island arc calc‐alkaline magma suffered fractional crystallization. In situ zircons Hf isotopic analyses yielded positive initial εHf(t) values ranging from 8.0 to 11.9 and the two‐stage Hf isotope crustal model ages (TDMC) of 554 to 807 Ma. It indicated that the rhyolite was derived from remelting of juvenile crust. The geochemical data for the rhyolites indicate that they were probably generated in a suprasubduction zone setting. It is proposed that the North Tianshan oceanic crust subducted northward beneath the Harlik–Dananhu arc during the Late Upper Carboniferous, and the rhyolites were derived from remelting of juvenile crust and generated in a suprasubduction zone setting.