新疆西准噶尔玛依勒山地区阔依塔斯杂岩体地球化学特征及锆石U-Pb年龄

Geochemical characteristics and zircon U-Pb ages of the Kuoyitasi complex body from Mayileshan area in western Junggar, Xinjiang

新疆西准噶尔北部广泛发育中酸性侵入岩,其形成时代为晚石炭世—早二叠世,岩石类型为辉石闪长岩、石英闪长岩和花岗闪长岩。阔依塔斯杂岩体的形成年龄为（297±2）Ma,Si O2为52.40%-67.53%;高Al2O3,14.92%-17.85%;里特曼指数（δ）小于3.3,介于1.47-1.98;富钠贫钾,K2O/Na2O为0.15-0.49;铁高而镁低,Fe OT/Mg O为1.01-1.69。其稀土配分模式右倾,轻重稀土分馏明显,具有微弱铕正异常。地球化学和年代学特征表明：岩体形成于后碰撞演化的晚期阶段,这一时间早于东准噶尔后碰撞的时间（二叠纪末）。该杂岩体主体可能为幔源岩浆底侵镁铁质下地壳,导致发生部分熔融的产物。

There are large-scale intermediate-acid intrusive rocks distributed in the north of western Junggar, Xinjiang. The rocks formed during late Carboniferous to early Permian. The typical plutons include pyroxene diorite, quartz diorite and granodiorite. The Kuoyitasi intrusion is among one of them. It has Si O2 values of 52.40%- 67.53%, high Al2O3content（14.92%- 17.85%） and Na content, and low K and Mg O content. Rittman values（δ） of the samples vary from 1.47 to 1.98, and the Fe OT/Mg O values arebetween 1.01 and 1.69. The REE patterns are characterized by LREE enrichment and slight Eu anomalies with obvious fractionation between LREE and HREE. The geochemical characteristics suggest that the Kuoyitasi intrusion formed in a post- collisional extensional tectonic environment, and should be formed earlier than the collision time of east Junggar terrain. The rocks were probably derived from partial melting of the lower crust which was intruded by mafic magmas.