青海省欧龙布鲁克微陆块东北缘红柳沟北镁铁——超镁铁质岩体形成时代及成因探讨  

Study on the Formation Age and Petrogenesis of Hongliugoubei Mafic——Ultramafic Intrusion,Northeastern Margin of Olongbuluck Micro-block in Qinghai

作　　者：周伟[1] 夏昭德[1] 杜玮[1] 夏明哲[1] 姜常义[1] 凌锦兰 赵彦锋 康珍 

机构地区：[1]长安大学地球科学与资源学院,西安710054 [2]陕西核工业集团公司,西安710100 [3]西北有色地质勘查局,西安710054 [4]中国科学院地质与地球物理研究所,北京100029

出　　处：《地质论评》2015年第6期1293-1304,共12页Geological Review

基　　金：国家自然科学基金项目(编号41302070;41102045);中央高校基本科研业务费(编号2013G1271100;2014G1271066);地质大调查项目(编号1212011121089)的成果

摘　　要：位于青海省欧龙布鲁克微陆块东北缘的红柳沟北镁铁——超镁铁质单式侵入体,其围岩为古元古代达肯大坂岩群(Pt1dk),主要由暗色橄榄辉长岩和辉长岩组成。岩体为中等富集Fe—Ti—P的铁质超基性岩体(m/f=2.66~3.04)。岩相学的观察表明岩石发育包橄结构、含长结构及堆晶结构,各造岩矿物的结晶顺序为橄榄石—→橄榄石+斜长石+斜方辉石→斜方辉石+单斜辉石+斜长石。各类岩石均富集轻稀土元素和大离子亲石元素,而亏损Nb、Ta。地球化学的信息显示岩浆在结晶过程中经历了一定程度的同化混染作用,混染源为上地壳物质,部分熔融作用发生于尖晶石稳定域内。采用SHRIMP锆石U-Pb法,获得岩体暗色橄榄辉长岩中锆石年龄为418.3±2.8Ma,属晚志留世。结合岩体的地球化学特征、形成年龄及区域地质资料,判断它应形成于大陆边缘伸展或裂谷化阶段,同时也佐证了柴达木盆地北缘晚志留世——晚泥盆世处于陆内伸展环境。The Hongliugoubei simple mafic—ultramafic intrusion is located in the northeastern margin of Olongbuluck micro-block,its wall rock is the Dakendaban Group( Pt1dk) of Palaeoproterozoic and the intrusion mainly composed of melaolivine——gabbro and gabbro. It's a moderately-enriched Fe—Ti—P ferruginous ultrabasic intrusion with m / f value being 2. 66 to 3. 04. The rocks from Hongliugoubei intrusion is well pervasive cumulatic texture,olivine-poikilitic texture and plagioclase-poikilitic texture. The crystallization sequence of minerals is olivine→ olivine + plagioclase + orthopyroxen—e→orthopyroxene + clinopyroxene + plagioclase. All kinds of the rocks from the intrusion are enriched in light rare earth elements( LREE) and large ion lithophile elements( LILE) and depleted in Nb,Ta. The Geochemistry information indicates that the magma has undergone some degree assimilation and contamination from upper crust. Partial melting process occurs in spinel stable field.SHRIMP zircon U-Pb age is 418. 3 2. 8Ma belonging to late Silurian. The Geochemical characteristics of this intrusion,formation age and regional geological data show that it forms in the extensional( or rifting) environment of ancient continental margin. It also suggests northern margin of Qaidam Basin is extensional during late Silurian to late Devonian.

关 键 词：柴达木盆地北缘 镁铁—超镁铁质岩体 年代学、地球化学 陆内伸展环境 

分 类 号：P588.1[天文地球—岩石学]