【摘要】 东昆仑地区广泛分布了大量花岗岩。已有的研究工作表明,东昆仑地区的花岗岩主要形成于晚二叠世-中三叠世和晚三叠世两个时期。本文提供了香日德地区二长花岗岩和花岗闪长岩的锆石U-Pb定年数据和全岩化学,稀土微量元素及Sr、Nd同位素地球化学研究资料,结合前人对该区不同时期花岗岩的研究成果,对香日德晚三叠世花岗岩的成因及其形成的动力学背景进行了讨论。研究表明东昆仑东段香日德地区的二长花岗岩和花岗闪长岩分别形成于223.2±1.7Ma和220.6±1.5Ma,属晚三叠世花岗岩浆作用的产物。根据该花岗岩的主量元素(特别是A/CNK比值),岩石富集大离子亲石元素(LILE:Rb、Th和K)和轻稀土(LREE),明显亏损高场强元素(HFSE:Nb、Ta、Ti和P),以及岩石具有相对高的Isr值(0.70820~0.71148)和相对低的εNd(t)值为-6.4~-3.6和较古老的模式年龄t2DM(1.5~1.7Ga)等地球化学特征,论证了该花岗岩的成因,指出香日德花岗闪长岩-二长花岗岩的起源和成因与碰撞后的背景下岩石圈的拆沉诱发的古老地壳物质的部分熔融作用有关,晚三叠世花岗岩岩浆作用是对自晚海西期以来幔源玄武质岩浆长期的底侵作用及地壳不断加厚的一种响应。它进一步证明在东昆仑地区,阿尼玛卿古特提斯洋的俯冲作用一直持续到早三叠纪,至晚三叠世才全面转入陆内碰撞造山阶段。晚三叠世花岗岩与晚二叠世-中三叠世花岗岩在暗色包体含量、岩浆混合作用的特征等方面的差异,可以用幔源物质贡献量的差异以及花岗质岩浆作用所经历的MASH过程的不同来解释。更多还原

【Abstract】 A large number of granites are widely distributed in the East Kunlun Orogen. Previous work indicates that the granites are mainly formed in the Late Permian-Middle Triassic and Late Triassic two periods. In this paper,we reporter Xiangride intrusion located in the eastern part of the East Kunlun orogen,which is composed of monzogranites and granodiorites,The LA-ICPMS U-Pb analyses suggest that the formation ages of granodiorites and monzogranites are 223. 2 ± 1. 7Ma and 220. 6 ± 1. 5Ma respectively. Granodiorites and monzogranites are characterized by enrichment of large lithophile elements( LILE,such as Rb,Th and K) and light rare earths element( LREE),significant negative anomalies of HFSE( eg. Nb,Ta,Ti and P),relatively high ISrvalues( 0. 70820 ~ 0. 71148),low εNd( t) values(- 6. 4 ~- 3. 8),and the older Nd isotopic model ages( the t2 DMvalues are 1. 5 ~ 1. 7Ga). The geochemical characteristics of the granites indicate that Xiangride intrusion is originated from partial melting of ancient crust which is resulted from magma underplating. Since the Late Hercynian mantle-derived basaltic magma underplated bottom of lower crust constantly and made it thickened,finally,the thickened crust occurred delamination in the Late Triassic. The subduction of the A’nimaque paleo-ocean was lasting up to the Early Triassic,and the Late Triassic witnessed the intracontinental collision. The systematic discrepancies between the Late Triassic granites and the Late Permian-Middle Triassic granites,in terms of the abundance of MMEs and magma mixing,can be explained by the different contribution from mantle materials and the diverse paths of the experienced MASH processes.更多还原