造山带环境中的东疆型镁铁-超镁铁杂岩  

THE EAST XINJIANG-TYPE MAFIC-ULTRAMAFIC COMPLEXES IN OROGENIC ENVIRONMENTS

作　　者：顾连兴[1] 诸建林 郭继春[1] 廖静娟[1] 严正富[1] 杨浩[1] 王金珠 

机构地区：[1]南京大学地球科学系,新疆地矿局第六地质大队

出　　处：《岩石学报》1994年第4期399-356,共1页Acta Petrologica Sinica

基　　金：国家自然科学基金;国家305攻关项目

摘　　要：新疆东部黄山－镜儿泉一带产有大－中型铜镍矿床的镁铁－超镁铁岩体是中石炭统弧后盆地引张环境下的热侵位产物，主要岩石类型有橄榄岩、辉橄岩、橄辉岩、二辉岩、辉长苏长岩、苏长辉长岩、辉长岩、橄长岩、辉长岩和闪长岩等；其超镁铁岩相对富铁．不具变质组构，并具橄榄石＋斜方辉石＋单斜辉石＋角闪石±斜长石矿物组合；岩石化学以富硅、贫碱、贫铝、贫钙为特征，并具拉斑玄武岩系演化趋势。这些岩体是造山带杂岩体的一种新类型，可称为东疆型。More than twenty mafic-ultramafic complexes occur in the Huangshan-Jing'erquan belt.These complexes are intruded in the Mid-Carboniferous back-arc sequences which has been metamorphosed to greenschist or amphibolite factes. They are equidimensional or lense-like in plan and several tens of metres or several kilometres in size.and are mostly funnel-shaped on cross section.Rock types are dominated by peridotite,pyroxine peridotite,olivine pyroxenite,troctolite,two-pyroxene pyroxenite, gabbroic norite,gabbro and diorite.There are no constant relations in space and time between mafic and ultramafic rocks.Ultramafic rocks in these complexes have relatively high Mg/Fe ratios and are characterized mineralogically by all assemblage of olivine + orthopyroxene + clinopyroxene + hornblende ± plagioclase without metamorphic textures.They contain olivines of Fo 75～90 with a majority of Fo 85～90,orthopyroxenes of En 76～95 and clinopyroxenes being predominated by cliopside and endiopside with minor augite(Al2O3=1.5%～4.8% ).The ultramafics have two sorts of hornblendes different ill appearence and composition.Granular hornblende has lower contents of titanium and was crystallized earlier,whereas poikilitic hornblende is higher in titanium and was formed at the latest stage of magma crystallization.Magnetite is a common accessary, but nowhere an economic concentration is reached.With the increase of plagioclase content ultramafic rocks will grade into mafic ones.Ultramafic rocks are characterized petrochemically by relatively high contents of silica and lower contents of alkali,aluminium and calcium with high Fe/Mg ratios and evolve along a tholeiitic trend.The primary magma of these complexes are postulated to be olivine-tholeiitic in composition.Several copper-nickel sulphide deposits large or middle in size have been defined by dimond drilling.The mafic-ultramafic complexes in the Huangshan-Jing'erquan belt were emplaced in an extensional environment of a Mid-Carboniferous back-arc basin.They are distinctive from the

关 键 词：造山带 镁铁-超镁铁 岩石成因 杂岩 

分 类 号：P588.36[天文地球—岩石学]