东昆仑造山带花岗岩及地壳生长  

Granitoids and Crustal Growth in the East-Kunlun Orogenic Belt

作　　者：莫宣学[1] 罗照华[1] 邓晋福[1] 喻学惠[1] 刘成东[2] 谌宏伟[1] 袁万明[1] 刘云华[3] 

机构地区：[1]中国地质大学,北京100083 [2]东华理工大学,南昌330013 [3]长安大学,西安7100643

出　　处：《高校地质学报》2007年第3期403-414,共12页Geological Journal of China Universities

基　　金：中国地质调查局重点基础研究花岗岩项目(200113900018);青藏高原基础地质调查成果集成和综合研究工作项目"青藏高原岩浆岩与大陆碰撞过程综合研究"(1212010610104);国家重点基础研究计划项目(2002CB41260)的资助

摘　　要：东昆仑造山带是青藏高原内可与冈底斯相媲美的又一条巨型构造岩浆岩带。该带内的花岗岩形成可以划分为4个时段,分别与4个造山旋回相对应:前寒武纪(元古宙);早古生代;晚古生代—早中生代;晚中生代—新生代。其中,以晚古生代—早中生代(或称华力西—印支旋回)、特别是三叠纪的花岗岩最为发育。东昆仑造山带基底主要形成于古元古代晚期。其早古生代构造-岩浆事件序列与北祁连造山带可以对比,属祁连—东昆仑加里东造山系统的一部分。到晚古生代—早中生代时东昆仑卷入古特提斯构造体制,属于古特提斯造山系统的北缘。华力西—印支是一个完整的造山旋回,与西南"三江"古特提斯的演化历史相似。昆南缝合带是当时中国南北大陆的主要构造分界线。新生代印度—欧亚大陆的碰撞,使东昆仑造山带又卷入了青藏大陆碰撞造山系统,但对东昆仑的影响是一种远程效应。东昆仑造山带大陆地壳主要形成于古元古代晚期,但在显生宙还有新生地壳(juvenilecrust)产生,与兴蒙、冈底斯、安第斯等造山带相似。东昆仑花岗岩带中丰富的幔源岩浆底侵作用与壳-幔源岩浆混合作用的证据,以及花岗岩类的Nd、Sr同位素成份(87Sr/Sr初始值多数小于0.710;εNd(t)值变化于-9.2和+3.6之间),说明86地幔物质的注入及其与地壳物质的混合,对显生宙地壳的形成演化起着重要作用,是显生宙东昆仑地壳生长的重要方式。根据花岗质寄主岩、镁铁质暗色微粒包体(MME)及底侵辉长岩的锆石SHRIMPU-Pb定年,东昆仑造山带在显生宙发生过两次大规模的底侵作用与岩浆混合作用,一次在早-中泥盆世(394～403Ma),另一次在中三叠世(239～242Ma),分别相当于加里东旋回、华力西-印支旋回的俯冲结束/碰撞开始阶段。The East-Kunlun orogenic belt （abbrev. EKOB） is one of major tectono-magmatic belts in the Tibetan plateau. Four stages of granitoid plutonism took place in Precambrian （the Proterozoic）, early Paleozoic （ ∈ -D3）, late Paleozoic-early Mesozoic （D3-T3）, and late Mesozoic-Cenozoic （after early Jurassic）, respectively. Among them, the late Paleozoic-early Mesozoic, especially Triassic granitoids are predominant. The basement of EKOB formed in late Paleo-Proterozoic. The early Paleozoic tectono-magmatic event sequence is comparable to that in the North- Qilian orogenic belt, and became a part of the Qilian-East-Kunlun Caledonian orogenic system. However, EKOB was involved in the Paleo-Tethyan tectonic regime during late Paleozoic-early Mesozoic period, and yielded an integrated Variscian-Indosinian orogenic cycle, similar to the Sanjiang Paleo-Tethyan orogeny. The south-Kunlun suture zone during that time was the main boundary between the north and the south China continents. Subsequently, EKOB was involved in the Tibetan collisional orogenic system in the Cenozoic since Indo-Eurasia collision. While the continental crust of EKOB mainly formed in late Paleo-Proterozoic, juvenile crust was also generated in the Phanerozoic time, similar to the Xing＇anling-Mongolia, the Gangdese and the Andes orogenic belts. There are abundant conclusive evidences of underplating and magma mixing in the East-Kunlun granitoid belt. Initial values of 87^Sr/86^Sr of the East-Kunlun granitoids are mostly less than 0.710 and εNd （t） values of them range from - 9.2 to ＋ 3.6. These features imply that inputting of mantle materials and mixing between mantle-and crust-derived materials played an important role in crustal generation and evolution in EKOB during the Phanerozoic time. According to SHRIMP U-Pb dating of zircons from granitoid host rocks, mafic microgranular enclaves （MMEs） and associated gabbros, two major events of underplating and magma mixing took place in EKOB in the early-middle Devonian �

关 键 词：东昆仑造山带 花岗岩 底侵作用 岩浆混合作用 地壳生长 

分 类 号：P588.1[天文地球—岩石学] P54[天文地球—地质学]