北山造山带公婆泉岩浆弧的组成、时代及其大地构造意义

Composition, Age and Polarity of Gongpoquan Arc and Its Tectonic Significance in Beishan Orogen

公婆泉岩浆弧近东西向展布于北山造山带牛圈子-洗肠井蛇绿混杂岩带北侧的公婆泉-石板井-小黄山一带,其物质组成、不同岩石组合的形成时代及其空间展布规律对于研究北山造山带早古生代地质构造演化具有十分重要的意义.在对三十余幅1∶5万区调填图数据研究分析的基础上,明确了公婆泉岩浆弧主要由510~470 Ma的辉长岩-闪长岩侵入岩组合和玄武岩、470~430 Ma片麻状英云闪长岩-花岗闪长岩和少量的闪长岩-石英闪长岩组合及大面积分布的安山岩、430~410Ma正长花岗岩-二长花岗岩组合等3期较强的构造岩浆作用组成.结合区域地质认识以及上述岩石组合的地球化学资料提出,3期岩浆作用分别形成于早期俯冲、主俯冲期和后碰撞期3个不同的构造演化阶段.其中主俯冲期的花岗岩组合的空间展布,具有由南向北的分布规律,物质提出指示了月牙山-洗肠井洋具有往北俯冲的极性.

Gongpoquan arc extends nearly east-west in Gongpoquan-Shibanjing-Xiaohuangshan area on the north side of NiuquanziXichangjing ophiolite mèlange belt in Beishan orogen.Its material composition,formation age of different rocks and spatial distribution pattern are very important for studying the Early Paleozoic tectonic evolution of Beishan orogen.Based on the study and analysis of data from more than 30 pieces of 1∶50000 regional geological mapping,It′s made clear that the Gongpoquan arc is mainly composed of three stages of strong tectono-magmatism,which are gabbro-diorite assemblages and basalts of 510-470 Ma,gneissic tonalites-granodiorite assemblages and a small amount of diorite-quartz diorite assemblages as well as large-scale andesite of 470-430 Ma,syenogranite-monzogranite assemblage of 430-410 Ma.Combined with the regional geological knowledge and the geochemical data of the above rock assemblages,they were formed in three different stages of tectonic evolution:initial subduction,main subduction and post collision periods.The spatial distribution of granite assemblages in the main subduction period has a distribution pattern from south to north.The variations of lithology indicates that the YueyashanXichangjing Ocean has a polarity of northward subduction.