大兴安岭中段央格力雅山地区扎文河岩体地球化学特征及其构造意义

Geochemistry and tectonic implications of the Zhawenhe intrusion in Yanggeliya Mountain area,central Great Xing’an Range

古亚洲洋在大兴安岭中段的构造演化长期以来争议不断,尤其是古生代岩浆活动亟待展开详细研究。本文在系统野外地质调查和岩相学分析的基础上,系统分析大兴安岭中段央格力雅山地区扎文河岩体的全岩地球化学特征,揭示其岩石成因,旨在深入对嫩江洋构造演化的理解。扎文河岩体主要由闪长岩、花岗闪长岩及正长花岗岩三个单元组成。三个岩石单元均为中钾—高钾偏铝质铁质岩石,相对富集轻稀土元素和大离子亲石元素,亏损重稀土元素和高产强元素,总体显示右倾型REE模式,但中—重稀土元素之间配分不明显,具有弱Eu负异常。闪长岩单元很可能是幔源玄武质岩浆分离结晶作用早—中期阶段的产物,并遭受了一定程度的俯冲流体交代。花岗闪长岩和正长花岗岩单元属于高钾钙碱性I型花岗岩,它们与闪长岩单元具有相同的岩浆源区,很可能是富集地幔玄武质岩浆分离结晶作用中—晚期阶段的产物。扎文河岩体形成于安第斯型大陆弧背景,指示早石炭世期间嫩江洋存在向兴安地块之下的俯冲,俯冲过程中所形成的挤压环境和岩浆活动反映了该时期古亚洲洋构造域在大兴安岭中段的构造演化。

The tectonic evolution of the Paleo-Asian ocean in the central Great Xing’an Range has long been controversial.Based on systematic field geological investigations and petrographic observations,this study presents new whole-rock geochemical data for the Zhawenhe intrusion from Yanggeliya Mountain area,central Great Xing’an Range,and deciphers its petrogenesis,in order to give a better understanding of tectonic evolution of the Nenjiang ocean.The Zhawenhe intrusion consists of three units,including diorite,granodiorite,and syenogranite.These three units are medium-high-K,metaluminous,ferroan rocks,they are enriched in light rare earth elements(LREE)and large ion lithophile elements(LILE),but depleted in HREE and high field strength elements(HFSE).They show right-sloping REE patterns with unobrials differentiated MREE and HREE,and have slight negative Eu anomalies.The diorite unit was probably derived by early-middle stage fractional crystallization of mantle-derived basaltic magma,and was metasomatized moderately by subduction-related fluids.The granodiorite and syenogranite units are high-K calc alkaline I-type granitoids,they origined from the same magma source of the diorite unit,and were possibly exporienced middle-late stage fractional crystallization of mantle-derived basaltic magma.The Zhawenhe intrusion was formed in an Andean-type continental arc setting,indicating that the Nenjiang oceanic plate was subducted beneath the Xing’an Block during the early Carboniferous.The compressional environment and magmatic activity related to the subduction processes may dominate the evolution of the Paleo-Pacific ocean tectonic regime in the central Great Xing’an Range.