【摘要】 藏东羌塘地块变质基底的时代归属和构造演化一直以来存在较大争议,沿龙木错-双湖缝合带东段出露的由酉西群和吉塘群组成的吉塘变质杂岩体成为解决这一问题的理想研究对象。本文对酉西群变质岩和吉塘群变质岩进行了系统的岩石学、岩相学、地球化学及锆石年代学研究。吉塘变质杂岩体的基底主要由中-新元古代的变沉积岩组成,其中酉西群岩性主要为云母绿泥钠长片岩,吉塘群则以黑云母二长片麻岩和黑云母斜长片麻岩为主,它们具有高Si O2、高Al2O3、富Fe OT、贫碱和贫钙的特征。微量元素均显示富集K、Rb、Th等大离子亲石元素(LILE),亏损Ti、Nb、Ta等高场强元素(HFSE),而Zr、Hf、Th、U等轻度富集则说明其源区更富集长英质组分而贫镁铁组分。碎屑锆石均为岩浆成因,年龄峰值范围为560～600Ma、808～865Ma、925～997Ma和1071～1119Ma,代表变质基底的年龄主要由泛非期和格林威尔造山期的构造-岩浆热事件所形成,在560Ma的沉积时代之前,源区可能发生有4次岩浆事件。地球化学特征和碎屑锆石组成指示酉西群和吉塘群原岩分别以泥砂质沉积岩和长英质粘土岩及砂砾岩等副变质岩为主。吉塘变质杂岩体所在的南羌塘地块与喜马拉雅地块和拉萨地块具有相近的物源区,故而认为南羌塘地块在中-新元古代期间可能属于冈瓦纳大陆的一部分。更多还原

【Abstract】 The characteristics and provenance of the metamorphic basement of the Qiangtang Terrane in eastern Tibet have been in controversial for a long time. The Jitang metamorphic complex consisting of the Youxi and Jitang groups along the Longmuco-Shuanghu Suture provides an ideal research subject to solve this problem. In this contribution, we present the petrology, petrography,geochemistry and zircon geochronology of metamorphic rocks from the Youxi and Jitang groups. Analytical results show that the Jitang metamorphic complex is composed of mica-chlorite-albite schist from Youxi Group and biotite monzonitic gneiss and biotite plagioclase gneiss from Jitang Group. The metamorphic complex is characterized by high Si O2,Al2 O3,Fe OT,with low alkaline and calcium. The trace elements show the enrichment of large ion lithophile elements( LILE) such as K,Rb,Th besides Ba,with strong depletion of Ti,Nb,Ta and other high field strength elements( HFSE). It is weakly enriched in Zr,Hf,Th and U,showing that these sedimentary rocks have more felsic components with minor mafic components. The detrital zircons are characterized by magmatic origin,with age peaks of 560 ～ 600 Ma,808 ～ 865 Ma,925 ～ 997 Ma and 1071 ～ 1119 Ma,indicating the evolution of the metamorphic basement is associated with Pan-African and Grenville tectonic-magmatic thermal events. The tectonic-magmatic thermal events of the orogenic period indicate that the source region may have four stage magmatic events before 560 Ma. The geochemical characteristics and detrital zircon dating indicate that these meta-sedimentary rocks of the Youxi and Jitang groups are dominated by argillo arenaceous sedimentary rocks and felsic-claystone and glutenite. Together with chronological characteristics,the Jitang metamorphic complex has similar provenance with the Himalayan and Lhasa terranes,confirming that the southern Qiang Terrane was probably a part of the Gondwana continent in Meso-Neoproterozoic.更多还原