西天山巴尔盖提花岗岩体年龄、地球化学特征与构造意义

Geochronology, geochemical properties and tectonic significance of Baergaiti granitoid in western Tianshan Mountain, NW China

高山林

Gao Shanlin

中国石化 石油勘探开发研究院, 北京 100083

SINOPEC Petroleum Exploration and Production Research Institute, Beijing 100083, China

巴尔盖提花岗岩体位于伊犁盆地北缘西天山博罗霍洛构造带。锆石LA-ICP-MS U-Pb年龄（374±7.0）Ma显示岩体侵位于晚泥盆世。岩石为斑状黑云母花岗岩，其主量元素SiO2、Al2O3、K2O、Na2O的含量分别为70.72%~79.12%，9.87%~14.51%，4.13%~5.54%，2.87%~4.35%，富碱、高钾、低镁钛，属高钾钙碱性系列；轻稀土相对富集，（La/Yb）N为7.61~16.31，具有显著的负Eu异常；相对富集大离子亲石元素Rb、U和Th等，亏损Nb、Ta和Ti等高场强元素，地球化学特征总体显示了I-A花岗岩过渡特征。区域上地层不整合关系、沉积特征及地球化学构造图解特征综合分析表明，巴尔盖提花岗岩体形成于晚泥盆世区域性造山后伸展背景，与石炭纪火山-沉积建造构成了晚古生代完整的开合构造演化旋回。

The Baergaiti granitoid is located in the Boluohuoluo tectonic belt in the western Tianshan Mountain of the Yili Basin. LA-ICP-MS zircon U-Pb shows age of 374±7.0 Ma, corresponding to the Late Devonian. Petrogeochemical analyses suggest that the intrusion belong to calc-alkaline metaliferous rocks characterized with high silica, potassium, and alkalinity, low magnesium and titanium. The contents of SiO2, Al2O3, K2O, Na2O range 70.72%-79.12%, 9.87%-14.51%, 4.13%-5.54%, 2.87%-4.35%, respectively. Meanwhile, the REE contents show an obvious rich LREE pattern ((La/Yb)N ranges 7.61-16.31) with negative Eu anomalies. Large ion lithophile elements such as Rb, Th and U are relatively enriched, whereas high strength field elements such as Nb, Ta and Ti are relatively depleted. Geochemical and isotope characteristics show a transition feature of high-K calc-alkaline I-A type granite. The analyses of a regional angular unconformity and sedimentary features suggest that the Baergaiti granitoid was deposited under a post-orogenic intra-continental extensional tectonic setting during the Late Devonian, and formed a complete tectonic evolution cycle coupling with the Carboniferous volcanic-sedimentary strata.

中国石化油田部项目“海域盆地勘探动态跟踪及选区评价部署研究”（G5800-16-ZS-YTB025）资助。

https://doi.org/10.11781/sysydz201703362