东昆仑夏日哈木地区二长花岗岩年代学、地球化学特征及地质意义

Geochronological and geochemical characteristics and geological significance of the monzogranite in Xiarihamu area of East Kunlun

东昆仑夏日哈木地区首次发现了早泥盆世二长花岗岩,对其开展年代学和地球化学特征研究,进一步探讨其岩石成因和构造地质背景。二长花岗岩锆石U-Pb年龄为(412.1±5.7)Ma(MSWD=0.95),形成于早泥盆世早期;岩石为过弱铝质亚碱性花岗岩,富SiO 2(含量为71.41%~72.46%)、K 2 O(含量为5.27%~6.16%),贫Fe 2 O 3(含量为1.86%~2.05%)、P 2 O 5(含量为0.08%~0.12%),富集轻稀土元素,具明显的负Eu异常;在原始地幔标准化微量元素蛛网图上可以看出,岩石明显富集Rb、Th、Zr、Hf,强烈亏损Nb、Sr、P、Ti、Ba。夏日哈木地区二长花岗岩属于I型花岗岩,其源岩可能由幔源岩浆底侵加热下地壳岩石致其部分熔融而形成,处于由同碰撞向后碰撞转换的构造环境,说明东昆仑夏日哈木地区在早泥盆世早期已进入伸展阶段。

The Early Devonian monzogranite was reported for the first time in Xiarihamu area of East Kunlun,so the authors investigated its geochronological and geochemical characteristics to further explore the petrogensis and tectonic setting.The U-Pb of zircon age of the monzogranite is(412.1±5.7)Ma(MSWD=0.95),which formed in early Early Devonian,and the monzogranite belongs to slightly peraluminous subalkaline series.The monzogranite is characterized by high SiO 2(71.41%~72.46%)and K 2O(5.27%~6.16%),low Fe 2O 3(1.86%~2.05%)and P 2O 5(0.08%~0.12%),and high LREE with obvious negative Eu anomalies.Rb,Th,Zr and Hf are obviously enriched,while Nb,Sr,P,Ti and Ba are strongly depleted on the primitive mantle-normalized trace element spider diagram.The monzogranite in Xiarihamu area belongs to I-type granite,and the magma of the source rock may come from the partial melting of the lower crust materials caused by the underplating heating of mantle-derived magma.The monzogranite was formed in the tectonic environment of syn-collision converting to post-collision,suggesting that Xiarihamu area of East Kunlun had been in the post-orogenic extension stage since early Early Devonian.