北祁连山东段苏家山高Mg埃达克岩地球动力学意义  

Sujiashan high-Mg adakite in the eastern section of North Qilian Mountains:implications for geodynamics

作　　者：王金荣[1] 吴继承[1,2] 贾志磊[1] 

机构地区：[1]兰州大学资源环境学院 [2]武警黄金技术学校,湖北襄樊441002

出　　处：《兰州大学学报（自然科学版）》2008年第3期16-23,27,共9页Journal of Lanzhou University(Natural Sciences)

基　　金：国家自然科学基金重点项目(40534020);甘肃省自然科学基金(ZS001-A25-006-Z)资助.

摘　　要：苏家山花岗闪长岩位于北祁连山东段，老虎山弧后盆地残留体北侧，侵入于原奥陶系阴沟群及前寒武纪变质岩系中，在空间分布上与米家山、扁强沟、清凹山、黄家凹山、银硐梁以及东侧南华山花岗岩共同构成长约220km的花岗岩带，沿NW-NWW向展布．地球化学研究结果表明：苏家山花岗闪长岩富Na贫K，属钙碱性系列；高Sr低Y，Yb，高Mg^#，Ni，Cr，可划归高Mg，Sr低Y型花岗闪长岩；微量元素蛛网图显示，岩石富集大离子亲石元素，亏损高场强元素及HREE，（w（La）／w（Yb））N〉22，δEu轻微负异常；K-Ar同位素年龄为425Ma．结果指示：苏家山花岗闪长岩具有高镁埃达克岩的特点，是在早古生代晚期北祁连东段造山作用过程中，滞留在地幔楔中的老虎山弧后盆地俯冲板片发生部分熔融，熔体与地幔橄榄岩发生明显的交代作用而形成．与此同时，阿拉善古陆南缘也卷入了造山作用，埃达克岩浆作用使陆壳在垂向上得以生长．Sujiashan granitoids are located in the eastern section of North Qilian Mountains and the north of the residue of Laohushan back-arc basin, intruding into what were originally called the Yin＇gou Group and Precambrian metamorphic rocks. From the west to the east, the granitoids of Mijiashan, Bianqianggou, Qing＇aoshan, Huangjiaaoshan, Yindongliang, Sujiashan and Nanhuashan compose a granitoid zone about 220 km long, stretching in NW-NWW. The geochemical results show that the Sujiashan granitoids have high Na and low K, belonging to calc-alkaline series; and high Sr low Y and Yb, Ni and Cr contents are compared with the typical adakites from the circum-Pacific, indicating they belong to the high-Mg andesites （adakites）. They are also obviously rich in LILE and LREE, and depleted in HSFE and HREE with slightly negative δEu, （w（La）/w（Yb））N〉22, and have K-Ar isotope age of 425 Ma. Similar to the geochemical characteristics of high-Mg adakite, the geochemical characteristics indicate that Sujiashan granitoids are derived from the partial melting of the subducted slab retaining in the mantle of Laohushan back-arc basin in the orogenic process of the eastern section of North Qilian Mountains in the late period of early Palaeozoic. The adakite magmatism cause the crust of the south continental margin of the Alxa to grow vertically.

关 键 词：高镁埃达克岩 板片熔融 地壳生长 北祁连山东段 苏家山 

分 类 号：P588.121[天文地球—岩石学] P534.1[天文地球—地质学]