内蒙古崇根山蛇绿岩前弧玄武岩的发现及其地质意义  

Discovery and Significance of the Fore-Arc Basalts from the Chonggenshan Ophiolite in Inner Mongolia

作　　者：王成 任利民[2] 张晓军[3] 余国飞 方磊 Wang Cheng;Ren Limin;Zhang Xiaojun;Yu Guofei;Fang Lei(Xinjiang Geological Survey Academy,Urumqi 830000,China;School of Earth Sciences,China University of Geosciences(Wuhan),Wuhan 430074,China;Faculty of Earth Resources,China University of Geosciences(Wuhan),Wuhan 430074,China;No.1 Geological Party of Hubei Geological Bureau,Huangshi Hubei 435100,China;No.266 Geological Party of Jiangxi Nuclear Industrial Geological Bureau, Nanchang 330038,China)

机构地区：[1]新疆地质调查院,乌鲁木齐830000 [2]中国地质大学(武汉)地球科学学院,武汉430074 [3]中国地质大学(武汉)资源学院,武汉430074 [4]湖北省地质局第一地质大队,湖北黄石435100 [5]江西省核工业地质局266大队,南昌330038

出　　处：《地质科技情报》2019年第3期1-11,共11页Geological Science and Technology Information

基　　金：中国地质调查局地质调查项目(1212011220448)

摘　　要：内蒙古崇根山SSZ型蛇绿岩位于兴蒙造山带北部的二连浩特-贺根山蛇绿岩带,为贺根山蛇绿岩中出露面积最大、岩性出露最为齐全的蛇绿岩块,主要组成端元为橄榄岩,少量堆晶辉长岩和拉斑玄武岩片。研究表明,该玄武岩为一套前弧玄武岩,岩性为低钾拉斑玄武岩。岩石w(SiO_2)为48.58%～51.23%,含较低的TiO_2(1.63%～2.08%),富Na_2O (3.13%～4.73%)而贫K_2O(0.05%～0.20%),Na_2O/K_2O为23.7～79.0;岩石具有亏损型稀土元素配分模式,类似N-MORB,微量元素富集Rb、Ba、U、Ta、Hf,亏损Th、Nb、Sr,元素质量分数普遍略高于N-MORB,与弧拉斑玄武岩相似。地球化学特征上兼具洋中脊与岛弧双重特点,且更偏向洋中脊,与马里亚纳前弧玄武岩(FAB)相一致。综合分析前人对于崇根山蛇绿岩块及区域蛇绿岩同位素年代学研究成果表明,二连浩特-贺根山蛇绿岩带在早石炭世存在前弧玄武岩,说明二连浩特-贺根山洋盆在早石炭世发生了洋内初始俯冲和洋陆转化岩浆作用。The Chonggenshan SSZ-type ophiolite is in the eastern part of the Erenhot-Hegenshan ophiolite belt that belongs to the Xing′anling-Mongolian Orogenic Belt. It is the largest of Hegenshan ophiolitic belts and is mainly composed of metamorphic peridotite and a few cumulate metagabbro and basalts.In this paper,the Chonggenshan basalts are thought to be fore-arc basalts. The basalts are low-K arc tholeiite with characterized by moderate concentrations of SiO2(48.58%-51.23%),low TiO2(1.63%-2.08%) and rich in Na2O(3.13%-4.73%) and poor in K2O(0.05%-0.20%) and high ratio of Na2O/K2O(23.7-79.0). They show light REE(LREE)-depleted chondrite-normalized REE patterns like N-MORB,rich in Rb,Ba,U,Ta,and Hf,depleted in Th,Nb,and Sr. However,the Chonggenshan basalts,compared with N-MORB,generally,show slightly higher content of trace elements,similar to those of island arc tholeiite(IAT).These geochemical characteristics indicate that the Chonggenshan basalts have both the characteristics of N-MORB and island arc tholeiite,and are more like N-MORB,which is consistent with the fore-arc basalts(FABs) of Mariana fore-arc. More comprehensive analysis of isotopic geochronology proves that Chonggenshan ophiolite and regional ophiolite belong to the Erenhot-Hegenshan ophiolite belt. This study holds that the Early Carboniferous fore-arc basalts exist in the Erenhot-Hegenshan ophiolite belt,and suggests that the Erenhot-Hegenshan ancient ocean began to subduct initially and occurred magmatism of the ocean-land transformation in Early Carboniferous.

关 键 词：前弧玄武岩 地球化学 早石炭世 崇根山SSZ型蛇绿岩 二连浩特-贺根山蛇绿岩带 

分 类 号：P588.145[天文地球—岩石学]