大兴安岭南段早白垩世早期后碰撞构造环境——来自林西县兰家营子辉长闪长岩的证据  

Early early-Cretaceous post-collisional tectonic setting of the southern segment of the Great Xing’an Range:Evidence from the Lanjiayingzi gabbro-diorite in Linxi area

作　　者：车亚文 刘建峰[1] 赵硕 葛茂卉 吕前露 CHE Yawen;LIU Jianfeng;ZHAO Shuo;GE Maohui;LYU Qianlu(Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China)

机构地区：[1]中国地质科学院地质研究所,北京100037

出　　处：《地质通报》2021年第1期152-163,共12页Geological Bulletin of China

基　　金：国家重点研发计划项目《北方东部复合造山带岩石圈三维架构与成矿地质背景》(编号:2017YFC0601301);国家自然科学基金项目《内蒙古东南部早—中三叠世镁铁质火山岩的成因及地质意义》(批准号:41472055);中国地质调查局项目《北方山系西拉木伦与贺根山基础地质调查》(编号:DD20190004)和《兴蒙造山带关键地区构造格架与廊带地质调查》(编号:DD20160201-01)。

摘　　要：对大兴安岭南段林西县以北兰家营子辉长闪长岩开展了系统的岩石学、锆石年代学和地球化学分析,以揭示该岩体的成因,并探讨大兴安岭南段早白垩世大地构造背景。锆石U-Pb定年结果表明,该岩体的形成时代为145.6±0.6 Ma,为早白垩世早期侵入体。地球化学分析结果表明,该岩体SiO2含量为53.38%~54.45%,K2O含量为1.34%~1.43%,Na2O含量为3.85%~4.05%,铝饱和指数A/CNK值介于0.8~0.9之间,属于钙碱性偏铝质岩浆岩。岩石的MgO和TFe2O3含量分别为5.44%~5.73%和7.53%~8.33%相应的Mg#值介于36.96~38.24之间,结合斜长石的环带和辉石的包橄结构,认为岩石是幔源原始岩浆经历分离结晶作用的产物。岩石相对富集Rb、Ba等大离子亲石元素,亏损Nb、Ta等高场强元素,锆石εHf(t)介于5.4~9.0之间指示岩浆起源于亏损的受俯冲流体交代过的岩石圈地幔。兰家营子辉长闪长岩与林西地区同时代A型花岗岩构成双峰式岩浆岩组合指示它们是伸展环境的产物。综合区域地质资料,认为大兴安岭南段早白垩世早期岩浆岩的形成与蒙古-鄂霍茨克洋闭合引起的碰撞后伸展背景有关。Based on the systematic petrology,zircon chronology and geochemistry analysis of the Lanjiayingzi gabiodiorite pluton in the north of Linxi County in southern Great Khingan Range,genesis of the pluton and the Early Cretaceous tectonic setting are discussed.Zircon U-Pb dating reveals that the pluton was formed in Early Cretaceous(145.6±0.6 Ma).Geochemistry of the pluton is characterized by 53.38%~54.45% of SiO2 contents,1.34%~1.43% of K2 O contents and 3.85%~4.05 % of Na2 O contents,with 0.8~0.9 of A/CNK,which indicates that the pluton belongs to a calc-alkaline metaluminous magmatic rock.Its MgO and TFe203 contents vary from 5.44%~5.73% and 7.53%~8.33% respectively,with 36.96 to 38.24 of Mg# values.Combined with the girdle of plagioclase and the poikilitic texture of olivine in clinopyroxene,it is suggested that the pluton was the product of the fractional crystallization of mantlederived primary magma.In addition,the pluton is relatively rich in LILEs such as Rb and Ba,and depletion in HFSEs such as Nb and Ta,with+5.4 to +9.0 of zircon εHf(t) values,which indicates that the pluton was derived from a depleted lithospheric mantle that experienced metasomatism from the subduction fluid.The Lanjiayingzi gabbrodiorite and coeval A-type granites in Linxi area constitute the bimodal magmatic assemblage,which suggests that they were formed in an extensional setting.Combined with regional geology,it is suggested that the formation of the Early Cretaceous magmatic rocks in southern Great Khingan Range has relation with the postcollision extensional setting resulting from closure of the Mongol-Okhotsk Ocean.

关 键 词：大兴安岭南段 辉石闪长岩 早白垩世 地球化学 岩石成因 

分 类 号：P588.12[天文地球—岩石学] P534.53[天文地球—地质学]