【作者】 辜平阳；

【导师】 李永军；

【作者基本信息】 长安大学 ， 构造地质学， 2009， 硕士

【摘要】 本文以西准噶尔西南达尔布特蛇绿岩为研究对象,从岩石组合特征、岩石学特征、岩石地球化学特征、构造环境、形成时代、就位机制及大地构造意义等方面对该混杂岩作了比较系统的研究,论文摘要如下:1.达尔布特蛇绿岩以片状蛇纹岩为基质,各构造岩块为其组成部分的构造混杂带。蛇绿岩中变质橄榄岩、堆积杂岩、基性火山岩较为发育,代表扩张机制的岩墙群规模很小,硅质岩不发育,斜长花岗岩呈岩枝状穿插于辉长岩中。空间位置关系上,蛇纹岩岩片出露位置最低,辉长岩、辉绿岩及玄武岩堆积于片状蛇纹岩中,薄层硅质岩覆盖在玄武岩之上。层序组合虽受构造破坏,但从总体来看仍是一组合比较完整的蛇绿岩。岩石变形变质强烈,普遍强蚀变碎裂岩化、黝帘石化、纤闪石化、糜棱岩化。2.达尔布特蛇绿岩中变质橄榄岩主量元素低TiO₂、Al₂O₃、CaO和全碱,富MgO特征,属镁质超镁铁岩,代表了原始地幔发生部分熔融的亏损地幔岩。稀土总量很低,轻稀土富集,呈“凹”型或“U”型分布。基性熔岩主量元素相对富MgO,贫Al₂O₃、K₂O、P₂O₅和ω（Na₂O）>ω（K₂O）。∑REE总体较低,稀土配分曲线表现为轻稀土亏损,重稀土平坦,类似于MORB型岩石。在此基础上富集LILE,Nb、Ta亏损,HFSE分异不明显,揭示岩浆源于亏损的地慢源区,表明其成因与俯冲作用有关。3.结合达尔布特蛇绿岩岩石地球化学特征和构造环境判别图解,推断其形成于消减带之上的弧后盆地环境。4.锆石U—Pb年龄为391.1±6Ma,MSWD=0.97（95%置信度）,形成时代属于中泥盆世。5.达尔布特断裂两侧石炭纪地层具有可比性,而非重要的岩相古地理、生物组合、变质作用、岩浆活动的分界线。说明达尔布特断裂不是洋盆闭合后的板块缝合带,可能是在弧后盆地拉张过程形成的深断裂,为镁铁—超镁铁质岩浆上涌的通道,或是在弧后盆地闭合过程中形成的推覆构造。6.达尔布特蛇绿岩的形成与洋盆主体消减时间相当,且是洋壳俯冲,弧后盆地被打开,导致新的洋壳（蛇绿岩）生成。最终在挤压机制下岩石向陆一侧拼贴就位。7.蛇绿岩带两侧沉积盆地属同一地层区,修正了过去曾以该蛇绿岩带作为地层分区的界线,将蛇绿岩带两侧沉积盆地划分为两个地层区的结论。更多还原

【Abstract】 This dissertation is object on Dalabute ophiolitic in Western Junggar,Xinjiang. Systemic researching the character of ophiolitic of rock combination、petrology、petrochemistry、geochemistry、tectonic setting、formtive age、emplacement mechanisms、tectonic significance and so on.1.It is composed of different tectonic blocks which come from ophiolitic,and chaotic matrixes which are slice serpentinite.The metaperidotites、cumulate complex、basic volcanic rock of Dalabute ophiolitic m（?）lange are more developmental,Siliceousrock and the scale of dike swarm which stand for spreading mechanism are small,plagiogranite apophysis interweave gabbro.The position of serpentinite is lowest,gabbro、diabase and basalt accumulate on the serpentinite,and siliceousrock cover with basalt.Although succession of strata is demolished,the combination of ophiolitic are integrated.The rocks are intensively deformation、pervasive metamorphose、cataclasis、zoisitization、uralitization and mylonitizaion.2.The metaperidotites of Dalabute ophiolitic m（?）lange,show low TiO₂、Al₂O₃、CaO and total alkali,high MgO,Mg^#,and have lowΣREE,enriched LREE,the rare earth element distribution patterns appear "凹" or "U",they are depletion pyrolite form primitive mantle which had undergone part melting.Basic rock show high MgO,low MgO,A1₂O₃、K₂O、P₂O₅andω（Na₂O）＞ω（K₂O）.The geochemical of basic rock characteristic of lowΣREE,depleted in LREE and HREE flat,unfractionated in HSF elements indicates that they are similar to a normal mid-ocean basalt（N-MORB）,meanwhile,samples are showing distinguishable enrichment in large-ion lithophile elements（LILE）,depeletion in Nb and Ta.They are indicate that the magma root depletion mantle,showing that it related with subdution.3.Combine the character of Dalabute ophiolitic of geochemistry with tectonic discrimination diagrams,it is reasonable suggest that the Dalabute ophiolitic was formed in a back-arc basin setting.4.Zircon U—Pb dating of gabbro from Dalabute ophiolite,give the age of 391.1±6.8Ma,MSWD=0.97（95%confidence）,indicating a Middle Devonian age of Dalabute ophiolite.5.Carboniferous stratum of both sides of Dalabute fault have some close characteristics,and the Dalabute rupture is not important boundary of lithofacies、biology combinnation、metamorphism、magmatic activity,showing that Dalabute fault was not suture belt after ocean basin closed,it may be a deep fault formed along witn the extention of back-arc basin,providing a channel for mafic magma intrusion,or a nappe structure with the closure of back-arc basin.6.The time of Dalabute ophiolitic came into being correspond with the ocean basin began to eliminate,it was new oceanic crust after oceanic crust beginning to subducted which induced back-arc basin was unclosed.Finally,Dalabute ophiolitic adhered to land after extrusion mechanism.7.Sedimentary basin beside Dalabute ophiolitic m（?）lange belong to a stratigraphic division,correcting a conclusion that the Dalabute ophiolitic m（?）lang was served as a borderline to two stratigraphic divisions.更多还原