东天山卡拉塔格晚石炭世岛弧火山岩

发现的地质意义

马志杰¹　柴凤梅¹　许强奋²　王　雯¹　毛启贵³　祁冬梅¹

（1. 新疆大学，新疆中亚造山带大陆动力学与成矿预测实验室 乌鲁木齐 830049；2. 新疆维吾尔自治区有色地质勘查局地球物理探矿队 乌鲁木齐 830013；3. 中国科学院新疆生态与地理研究所矿产资源研究中心 乌鲁木齐 830049）

摘　要　东天山大南湖岛弧带内古生代火山岩地层时代一直存在争议，其北部卡拉塔格地区核部火山岩尤为复杂。本研究通过详细的野外工作，在该区识别出一套晚石炭世（299.6±2.1 Ma）流纹岩地层。地球化学研究表明：流纹岩具有高SiO₂（75.83%~77.96%）、低Al₂O₃（10.41%~11.94%）和TiO₂（0.30%~0.34%）含量，富钠贫钾（Na₂O/K₂O=52~215），莱特碱度率（A.R.）为2.84~3.28，属钙碱性低钾系列岩石；所有岩石显示轻微富集大离子亲石元素和轻稀土元素(La/Yb)_N = 2.12~2.43、亏损髙场强元素Nb、Ta和Ti，并呈现Eu负异常（Eu/Eu^*=0.64 ~ 0.82），与俯冲相关的钙碱性岛弧岩浆岩特征相似。结合区域研究成果，本文认为该流纹岩是北天山洋向北俯冲过程中岩浆活动的产物，晚石炭世北天山洋尚未闭合。本研究成果为东天山大南湖岛弧带岩浆活动时限和构造演化提供了新资料。

关键词　流纹岩　岛弧火山岩　锆石U-Pb年代学　地球化学　卡拉塔格　东天山

The discovery of Low-Carboniferous arc volcanic rocks and its tectonic signifance at the Kalatag area in the eastern Tianshan

Ma Zhijie¹　Chai Fengmei¹　Xu Qiangfen²　Wang Wen¹　Mao Qigui³　Qi Dongmei¹

（1. Xinjiang Key Laboratory for Geodynamic Processes and Metallogenic Prognosis of the Central Asian Orogenic Belt, Xinjiang University, ürümuqi 830049；2. Geophysical Exploration Party of Xinjiang Geoexploration Bereau for Nonferrous Metals,

ürümuqi 830011；3. Xinjiang Research  Center for Mineral Resources, Xinjiang Institute of Ecology and Geography,

Chinese Academy of Sciences, ürümuqi 830049）

Abstract　Kalatage area is located in the Dananhu island arc belt on eastern Tianshan, Xinjiang, China, and volcanic age was extensively controversial in the cluster area. Based on fieldwork, we have discovered a new set of rhyolite strata of Late Carboniferous (299.6±2.1 Ma). Geochemical data shows that they are characterized by high SiO₂ (75.83%~77.96%), low Al₂O₃ (10.41%~11.94%) and TiO₂ (0.30%~0.34%) contents. Additionally, Na₂O/K₂O and Wright alkalinity ratio (A.R.) range from 52~215 and 2.84~3.28, respectively, indicating that rhyolites belong to calc-alkaline and low potassium series. The rhyolites are negative Eu anomalies (Eu/Eu^*=0.64~0.82) and relatively enriched in large ion lithophile elements (LILE) and depleted in high field strength elements (Nb, Ta, Ti) and exhibit LREE-enriched (La/Yb)_N=2.12~2.43, which is similar to the characteristics of subduction-related calc-alkaline island-arc magmatic rocks. Combined with previous findings, the rhyolites formed in an island arc environment related to the northward subduction of the North Tianshan Ocean, indicate that the North Tianshan  Ocean was not closed during the Late Carboniferous. This discovery provides new data in understanding the time limit of magmatic activity and tectonic evolution of the Dananhu arc belt of the eastern Tianshan.

Keywords　Rhyolite, Island arc volcanic rock, Zircon U-Pb dating, Geochemistry, Kalatag, Eastern Tianshan

新疆东天山大南湖岛弧带位于中亚造山带南缘，是研究古亚洲洋俯冲作用、弧—陆碰撞等演化过程的关键地区之一（马瑞士等, 1997；Xiao et al., 2004；王京彬等, 2006；Mao et al., 2014, 2021；Zhang et al., 2018；Zhao et al., 2020）。目前岛弧带内的地层年代学格架及其构造背景尚有争议，尤其以大南湖岛弧带北部卡拉塔格隆起核部含矿火山—沉积岩地层的时代归属问题争议较大，如：一些学者认为是下古生界地层^①②（毛启贵等, 2010；李玮等, 2016；龙灵利等, 2017；Chai et al., 2019）；部分学者将其划分为下泥盆统卡拉塔格组^③（唐俊华等, 2006；陈磊等, 2018）；也有一些学者认为其形成时代为奥陶纪—石炭纪（Mao et al., 2014, 2021；Yu et al., 2019）。地层归属问题也使得大南湖岛弧带古生代期间的构造环境的认识更加复杂。

本研究对卡拉塔格核部地层开展了详细的野外地质工作，发现了晚石炭世流纹岩地层，对其进行了岩相学和元素地球化学分析，以期为卡拉塔格核部地层火山作用研究提供新证据，为东天山大南湖岛弧带构造演化研究提供新依据。                                             

图1　东天山矿产地质图（据Mao et al., 2018修编）

Fig. 1　Geological map of metal deposits in East Tianshan (modified after Mao et al., 2018)

① 新疆维吾尔自治区地质矿产勘查局地质调查院. 2003. 1∶250 000 五堡幅（K46C002002）区域地质调查报告.

② 北京矿产地质研究院. 2016. 卡拉塔格铜（锌）矿整装勘查区1∶50 000六幅区域地质矿产调查报告.

③ 新疆地质矿产局第一区域地质调查大队. 1988. 1∶200 000康古尔塔格幅（K-46-XIV）区域地质调查报告及地质图.

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