东昆仑造山带三叠纪岩浆混合成因花岗岩的岩浆底侵作用机制  

Underplating mechanism of Triassic granite of magma mixing origin in the East Kunlun orogenic belt

作　　者：谌宏伟[1] 罗照华[2,3] 莫宣学[2,3] 刘成东[4] 柯珊[2] 

机构地区：[1]中国地质大学北京市水资源与环境工程重点实验室 [2]中国地质大学地球科学与资源学院 [3]教育部岩石圈构造,深部过程及探测技术重点实验室,北京100083 [4]东华理工学院地球科学与资源信息系

出　　处：《中国地质》2005年第3期386-395,共10页Geology in China

基　　金：中国地质调查局地质大调查项目(200113900069-4-3;200113900018-5)资助。

摘　　要：东昆仑造山带广泛出露三叠纪岩浆混合成因花岗岩,它们具有共同的特征:岩体成分变化大;花岗岩类岩石中富含镁铁质微粒包体(maficmicrogranularenclave——MME);不同岩性之间常常呈渐变过渡关系。同时,这些岩体无一例外都和代表下地壳的深变质岩共生,暗示岩浆就位于地壳深部。此外,东昆仑地区广泛发育基性侵入体,它们产在深变质岩中,或者与岩浆混合成因花岗岩类共生,暗示下地壳物质的部分熔融和岩浆混合成因花岗岩的形成有可能与基性岩浆底侵作用有关。笔者选择东昆仑加鲁河这一典型的岩浆混合成因花岗岩体为例,对其岩石学、地球化学、同位素地球化学等特征进行了详细研究,认为幔源岩浆底侵作用是这类岩体形成的直接原因,并对幔源岩浆底侵作用和岩浆混合成因花岗岩之间的成因联系以及幔源岩浆底侵作用在东昆仑造山带三叠纪地壳生长和构造演化中所起的重要作用进行了讨论,构建了加厚陆壳背景下的断离—底侵—混合—拆沉作用模型。Triassic granites of magma mixing origin are widespread in the East Kunlun orogenic belt. They have the following common features： the composition of granites varies greatly; granites contain abundant mafic microgranular enclaves （MME）; and different rock types tend to show gradational relationships. Particularly, these rocks co-exist with low-grade metamorphic rocks representing the lower crust without exception, implying that the magma was emplaced in the deep crust. In addition, basic intrusive rocks are widely developed in the area.They either occur in high-grade metamorphic rocks or occur together with granites of magma mixing origin,suggesting that partial melting of the lower crust and formation of the granites of magma mixing origin are probably related to underplating of basic magma. Take for example the Jialuhe granite--a typical granite intrusion of magma mixing origin in the East Kunlun area, the authors studied in detail its petrological, geochemical and isotope geochemical characteristics. It is concluded that the mantle-derived magma underplating was the direct cause of the formation of such granites and played an important role in the Triassic crustal growth and tectonic evolution in the East Kunlun orogenic belt. Furthermore, the genetic relation between the mantle-derived magma underplating and granites of magma mixing origin is discussed and a model of breaking-off-underplating-mixing-delamination in the setting of the thickened continental crust is constructed.

关 键 词：幔源岩浆底侵作用 岩浆混合作用 镁铁质微粒包体(MME) 三叠纪 东昆仑 

分 类 号：P588.121[天文地球—岩石学]