摘要
东昆仑造山带中灶火地区镁铁质岩墙群以闪长玢岩为主,含少量闪斜煌斑岩、辉绿玢岩及辉绿岩,LA-ICPMS锆石U-Pb年代学指示该套岩墙群结晶侵位年龄为（249±1）Ma。稀土元素含量整体较高,富集轻稀土元素（∑REE=99.9×10-6~173.9×10-6,（La/Yb）N=3.5~9.3）;微量元素表现出富集大离子亲石元素（LILE）,亏损高场强元素（HFSE）的特征;源区分析表明,镁铁质岩浆为俯冲洋壳析出的流体交代富集地幔的结果,且在岩石成因中部分熔融起到主导作用,地壳混染和分离结晶作用对岩浆成分分异起到的作用有限。构造环境分析表明,岩石的形成与俯冲作用有关,结合区域构造演化认为镁铁质岩墙群的成因为：早三叠世,在古特提斯洋向北俯冲的环境下,俯冲板片释放的流体交代富集地幔,诱发地幔部分熔融形成镁铁质岩浆,受弧后伸展的动力学背景影响,岩浆最终上升侵位形成镁铁质岩墙群。
The Zhongzaohuo mafic dyke swarms in East Kunlun are principally composed of dioritic porphyrite with minor lamprophyre, porphyritic diabase, and diabase. The LA-ICP-MS zircon U-Pb dating indicates that the mafic dykes were emplacedat（249 ± 1） Ma. The mafic dykes are enriched in LILE and depleted in HFSE. The rocks have higher total REE,with slightly enriched LREE（∑REE=99.9×10-6~173.9×10-6,（La/Yb）N=3.5~9.3）. Source region analysis shows that mafic magma resulted from the fluid from subducted ocean crust and the mantle metasomatism, and partial melting played a dominant role in magma evolution,while crustal contamination and fractional crystallization played a limited role in magmatic differentiation. Tectonic setting analysis shows that the formation of the rocks was related to subduction; in combination with the tectonic evolution of East Kunlun, the authors hold that the formation process of mafic dyke swarms in this paper is as follows： in early Triassic, as the result of northward subduction of Paleo- Tethys Ocean, fluids from the subduction slab were dehydrated and mantle peridotite experienced metasomatism, which promoted the mantle peridotite partial melting into mafic magma; the magma was affected by the dynamic background of the back-arc extension, and then it migrated upward to the upper crust along the fissures to form the mafic dykes.
出处
《中国地质》
CAS
CSCD
北大核心
2015年第5期1457-1470,共14页
Geology in China
基金
中国地质调查局地质调查项目(1212010918021)资助
