东昆仑造山带晚三叠世岩浆混合作用:以和勒冈希里克特花岗闪长岩体为例

摘要

In the East Kunlun orogenic belt (EKOB),mafic microgranular enclaves (MME) occur frequently in Late Permian-Triassic granitic rocks.In this paper,the authors took Helegang Xilikete granodiorites in the eastern part of the EKOB as an example to study their host rocks and MME in detail.Characteristics of the host rocks and the MME,such as field occurrence,morphology,texture and structure and mineralogy,together with the geochemistry,show that they were cooled and crystallized in a short time immediately after the intrusion of basaltic magma into intermediate-acidic magma and thus have similar distribution patterns to the host rocks in the REE diagram and trace element spider diagram,such as the enrichment of the LtEE and LILE and the depletion of the HREE and HFSE,reflecting a typical feature of magma mixing.The result of LA-ICP-MS zircon geochronology implies that the crystallization age of the MME is about 224.9±4.1 Ma,very close to that of the host rock (225±5 Ma),suggesting a crust-mantle magma mixing event at the stage of post-collision in the EKOB in Late Triassic.%东昆仑造山带晚华力西期-印支期花岗质岩石中广泛发育暗色微粒包体.本文以东昆仑东段和勒冈希里克特花岗闪长岩体为例,对暗色微粒包体及其寄主岩进行了详细研究.包体的野外产出特征、形态、结构构造和矿物学特征表明,他们是基性岩浆进入中酸性岩浆快速冷凝结晶的产物,和寄主花岗岩有着相似的稀土元素配分模式,显示轻稀土富集,重稀土亏损,轻重稀土元素分馏明显的特征,微量元素蛛网图也具有明显的相似性,富集大离子亲石元素,亏损高场强元素,反映了岩浆混合作用的特征;LA-ICP-MS锆石U-Pb同位素年代学研究显示,暗色微粒包体的形成年龄为(224.9±4.1)Ma,与寄主岩的同位素年龄值(225±5)Ma在误差范围内一致,表明了在晚三叠世期间东昆仑地区存在着后碰撞阶段壳-幔岩浆混合作用.