甘肃北山地区芦草沟富闪深成岩的成因  

Petrogenesis of Lucaogou Appinities in the Beishan Area of Gansu Province,NW China

作　　者：余吉远[1,2,3] 计波 王国强[1,2,3] 卜涛 过磊[1,2] YU Jiyuan;JI Bo;WANG Guoqiang;BU Tao;GUO Lei(Xi’an Center,China Geological Survey,Xi’an 710054,Shaanxi,China;Northwest China Center Geoscience Innovation,Xi’an 710054,Shaanxi,China;Orogen Research Center of China Geological Survey,Xi’an 710054,Shaanxi,China)

机构地区：[1]中国地质调查局,西安地质调查中心,陕西西安710054 [2]西北地质科技创新中心,陕西西安710054 [3]中国地质调查局造山带地质研究中心,陕西西安710054

出　　处：《大地构造与成矿学》2023年第2期461-472,共12页Geotectonica et Metallogenia

基　　金：中国地质调查局地质调查项目(DD20230005,DD20230215,DD20230334);国家自然科学基金项目(41202045,41703038);陕西省自然科学基金项目(2023-JC-YB-233)联合资助。

摘　　要：富闪深成岩是一类罕见的岩石类型,角闪石含量很高,矿物组合十分罕见,对岩浆作用和地球动力学过程具有敏感的指示意义。本文对甘肃北山地区首次发现的芦草沟二叠纪富闪深成岩开展野外调查、LA-ICP-MS锆石U-Pb测年、全岩主量和微量元素地球化学分析,结果表明,岩石的SiO_(2)含量为45.43%~51.84%,Na_(2)O含量为2.76%~3.98%,K_(2)O含量为0.18%~0.59%,Al_(2)O_(3)含量为16.59%~20.58%,MgO含量为4.18%~6.34%,显示贫钾富钠的特征;岩石的微量元素组成显示富集大离子亲石元素Rb、Ba、U等,亏损高场强元素Nb、Ta、Zr和Hf,Eu异常不明显(δEu=0.81~1.46)。锆石U-Pb年龄为286.7±2.5 Ma,即形成于早二叠世。结合区域地质背景,认为芦草沟富闪深成岩是俯冲碰撞环境壳幔相互作用的产物,而中亚造山带大范围发育中晚二叠世花岗岩是碰撞后构造岩浆事件的产物,暗示北山地区的古亚洲洋在中二叠世才完全消亡,进入陆内演化阶段。Appinite is a rare type of igneous rocks,which is a sensitive indicator of magmatic and geodynamic processes.This paper reports the discovery of the Lucaogou Permian appinite in the Beishan area,Gansu province.With aims to improve the understanding of the tectonic evolution of the Beishan area,a systematic investigation of the geological and tectonic background,age,and petrogenesis of the appinite was carried out.Zircon U-Pb dating of the appinite yielded a weighted ^(206)Pb/^(238)U mean age of 286.7±2.5 Ma.The appinite is characterized by moderate SiO_(2)(45.43%to 51.84%),relatively rich Na_(2)O(2.76%to 3.98%)and low K_(2)O(0.18%to 0.59%),enriched in LILE(Rb,Ba,U)and depleted in HFSE(Ti,Nb,Ta,Zr and Hf),and obvious positive Eu anomalies(0.81 to 1.46).Combined with the regional geological background,it is considered that the appinite is the product of crust-mantle interaction in a subduction collision environment,while the middle-late Permian granites in the Central Asian orogenic belt are post-collisional.We,therefore,suggest that the ancient Asian Ocean in the Beishan area was completely closed and evolved into intracontinental regime in the middle Permian.

关 键 词：LA-ICP-MS锆石U-PB年龄 富闪深成岩 地球化学 岩石成因 俯冲‒碰撞 甘肃北山 

分 类 号：P597[天文地球—地球化学] P595[天文地球—地质学]