东昆仑西段落雁山花岗闪长斑岩年代学、地球化学特征及地质意义

Chronology,Geochemistry and Geological Significance of Luoyanshan Granodiorite Porphyry in the West Section of East Kunlun

东昆仑造山带发育大量花岗质岩浆岩,对其研究不仅能为东昆仑的岩浆、构造提供新的信息,且对探讨古特提斯的构造-演化过程具重要意义。本文报道东昆仑西段落雁山花岗闪长斑岩体的两组锆石U-Pb年龄和地球化学数据,并对其成因及构造意义进行探讨。两组落雁山花岗闪长斑岩体锆石^(206)Pb/^(238)U-年龄分别为(312.4±2.0)Ma、(312.4±2.2)Ma,形成于晚石炭世。岩石地球化学特征显示,该岩体具高钾钙碱性准铝质花岗岩特征,稀土元素标准分布曲线呈右倾,富集轻稀土,轻、重稀土分异明显,微量元素中大离子亲石元素(LILE:Rb,Ba)相对富集;高场强元素(HFSE:Nb,P,Ti)亏损。锆石Hf同位素特征和岩石成因物源研究表明,落雁山花岗闪长斑岩为少量幔源岩浆参与的壳幔混源I型花岗岩。据区域构造研究,落雁山花岗闪长斑岩形成于晚石炭世古特提斯洋壳俯冲作用背景下的岛弧晚期岩浆活动。

A large number of granitic magmatic rocks are developed in the East Kunlun orogenic belt,and its research can not only provide new information for the magma and structure of the East Kunlun,but also has important significance for exploring the tectonic-evolution process of Paleo-Tethys.This article reports two sets of zircon U-Pb age and geochemical data of the Yanshan granodiorite porphyry in the western section of the East Kunlun Mountains,and discusses its genesis and tectonic significance.The two sets of LA-ICP-MS zircon U-Pb dating results of the Luoyanshan granodiorite porphyry body are(312.4±2.0)Ma and(312.4±2.2)Ma respectively,which were formed in the Late Carboniferous.The rock geochemical characteristics show that the rock body has the characteristics of high-potassium calcium-alkaline quasi-aluminum granite.The standard distribution curve of rare earth elements is right-leaning.It is rich in light rare earths and has obvious differentiation between light and heavy rare earths.Among the trace elements,large ion lithophile elements(LILE:Rb,Ba)are relatively enriched;high field strength elements(HFSE:Nb,P,Ti)are depleted.Studies on zircon Hf isotopic characteristics and petrogenesis and provenance indicate that the Luoyanshan granodiorite porphyry is a type I granite with a small amount of mantle-derived magma.According to regional tectonic research,the Luoyanshan granodiorite porphyry was formed in the late Carboniferous Paleo-Tethys oceanic crust subduction-related background during the late island arc magmatic activity.