【作者】 卢荣辉；

【导师】 姜常义；

【作者基本信息】 长安大学 ， 矿物学、岩石学、矿床学， 2010， 硕士

【摘要】 红石山镁铁质-超镁铁质层状岩体位于塔里木板块东北部的新疆北山地区。北山地区是我国主要的镁铁质-超镁铁质杂岩带之一,已发现该类杂岩体近百个,红石山岩体是其中最具代表性的镁铁质-超镁铁质层状岩体之一。本文通过对红石山岩体岩相学、晶体化学、稀土元素、微量元素和Nd、Sr、Pb同位素方面的系统研究,科学论证了其岩浆过程、岩浆性质、地幔源区特征。通过研究取得的了以下几点初步认识：1、红石山镁铁质-超镁铁质层状岩体存在两种岩相：橄榄岩相和辉长岩相。两种岩相是同源岩浆演化到不同阶段的产物。橄榄岩相的岩石类型有：纯橄岩、单辉橄榄岩、含长橄榄岩、橄长岩；辉长岩相的岩石类型有：橄榄辉长岩、辉长岩、斜长岩。橄榄岩相岩石化学成分明显富MgO、FeOT,贫CaO、Al2O3, m/f=5.74-8.76,属铁质-镁质超基性岩；辉长岩相岩石化学成分明显富CaO、Al2O3,贫MgO、FeOT, m/f=1.81-4.56,属铁质超基性岩。橄榄岩相与金属硫化物矿化关系密切,而辉长岩相与磁铁矿化关系密切。红石山岩体呈岩盆状,形成于早二叠世。2、红石山岩体是一堆晶层理非常发育的镁铁质-超镁铁质层状岩体。通过对2个钻孔的编录,红石山岩体至少可以划分为4个旋回,每一个旋回代表着一次岩浆贯入,各个旋回之间堆晶韵律明显,完整的堆晶韵律为“纯橄岩+单辉橄榄岩+含长橄榄岩+橄长岩+橄榄辉长岩+辉长岩+斜长岩”。3、红石山层状岩体岩石结构以正堆晶结构为主,堆晶矿物为橄榄石、尖晶石、斜长石和磁铁矿,填隙相主要为单斜辉石。岩相学和地球化学特征表明岩浆在演化过程中经历了橄榄石、尖晶石、斜长石、单斜辉石和磁铁矿的分离结晶作用,结晶次序为橄榄石+尖晶石→橄榄石+尖晶石+单斜辉石→橄榄石+尖晶石+斜长石→橄榄石+斜长石+单斜辉石→斜长石+单斜辉石+磁铁矿。4、红石山岩体稀土元素和微量元素含量都很低,为原始地幔的1-10倍。稀土元素配分曲线大体上表现为平坦型,相对富集大离子亲石元素,相对亏损TiO2、P2O5、Na2O、K20和高场强元素,具有不同程度的正铕异常。Nd、Sr、Pb同位素特征表明红石山岩体源自于亏损型地幔,局部与围岩发生了同化混染作用。5、原生岩浆属苦橄质岩浆,这种高温高镁的苦橄质岩浆是地幔柱轴部部分熔融形成的,这为塔里木东北部早二叠纪地幔活动提供了确凿的证据。更多还原

【Abstract】 Hongshishan mafic-ultramafic layed intrusion lies in the Beishan zone in Xinjiang, northeast of the Tarim plate.The Beishan zone is one of the most important mafic-ultramafic layed complex zone in China.lt is reported that almost hundreds of such intrusions has been found in this area, while the Hongshishan intrusion is one of the most representative mafic-ultramafic intrusions. According to systematically research the petrography, crystal chemistry, rare earth elements, trace elements and Sr, Nd, Pb isotopic geochemistry of Hongshishan intrusion, it’s demonstrateed its magmatic process, magma nature and mantle source district features in this paper. Based on such researches,we get some initial understanding as follows:1. In the Hongshishan mafic-ultramafic layed intrusion, there are two phases:peridotitic facies and gabbroic.facies,which are products of different stages of comagmatic rock.The facies units of the peridotitic facies are dunite,clinopyxene peridotite,peridotite,feldspathic peridotite,troctolite,while the gabbroic facies are olivine gabbro,gabbro,anorthosite. MgO as well as FeOT are rich and CaO、Al2O3 poor in the peridotitic facies,the m/f ratio is 5.74-8.76 and belong to ferruginous-magnesium ultrabasic rocks,while CaO、Al2O3 are rich and MgO、FeOT are poor in the gabbroic facies,the m/f ratio is 1.81-4.56 and belong to feruginous ultrabasic rocks. The peridotitic facies have a relation with sulfide metallization,while the gabbroic facies with magnetite metallization. The intrusion is a chonolith,forming in the Early Permian.2.The Hongshishan intrusion is a mafic-ultramafic layered intrusion with cumulate bedding well development.After researchs on two cores,at least four cycles can be classified in the Hongshishan intrusion,and every cycle can be representative for a magma injection.The cumulate rhythmicities are obvious in every cycles,and a complete cumulate rhythmicity should be dunite+clinopyroxene peridotite+ feldspathic peridotite+ troctolite+ olivine gabbro+gabbro+anorthosite.3.The orthocumulate texture is the primary texture in the Hongshishan intrusion. The cumulate minerals is olivine,spinel, plagioclase,magnetite,and the intercumulate mainerals is primaryly clinopyroxene.Petrography and geochemistry characters shou that the Hongshishan intrusion had undergone fractional crystallizition of olivine,spinel,plagioclase,clinopyroxene and magnetite in the magma evolution,with crystallization order of olivine +Cr-spinel→olivine+Cr-spinel+clinopyroxene→olivine+Cr-spinel+ plagioclase→olivine+ plagioclase+ clinopyroxene→plagioclase+ clinopyroxene+ magnetite.4. The concentrations of rare earth elements and trace elements are very low with 1 to 10 times for that of the primitive mantle.The REE patterns are flattened,with positive Eu anomalies to different extent.The Large Ion Lithpophile Elements (LILE) are enriched,while TiO2、P2O5、Na2O、K2O as well as high field-strength elments(HFSE) depleted in the Hongshishan intrusion. The characters of Nd、Sr、Pb isotopes show that the magmatic source belong to the depleted mantle (DM),and it was locally inflenced by contamination with the wall rocks.5. The primary magma of the Hongshishan intrusion belong to Mg-enriched and high-temperature picritic magma,which forms in the axle center of mantle plume under fraction melting.It is a conclusive evidence to mantle plume of northeast Tarim Plate.更多还原