新疆伊犁地块南缘志留纪和泥盆纪花岗质侵入体锆石SHRIMP定年及其形成时构造背景的初步探讨

Zircon SHRIMP dating of Silurian and Devonian granitic intrusions in the southern Yili block,Xinjiang and preliminary discussion on their tectonic setting

位于新疆西天山的伊犁地块南缘发育大量古生代侵入岩,本文从前人划分的华力西期侵入岩中识别出泥盆纪和志留纪的中酸性侵入岩,对其中三个侵入体的锆石进行SHRIMP U-Pb定年研究,分别获得436±8Ma、370±7Ma、366±8Ma的^(206)Pb/^(238)U表面年龄;同时对其岩石学和地球化学进行了研究,结果显示该区志留纪、泥盆纪侵入岩均具有较典型的活动陆缘侵入岩的特征,结合该活动陆缘区域岩浆活动资料以及前人研究成果,初步确定志留纪至早石炭世期间,南天山碰撞造山带前身洋盆的洋岩石圈板块一直在向伊犁地块之下俯冲。

In the southern margin of Yili block, west Tianshan, Xinjiang, there are a lot of granitic intrusions which had been previously thought to be emplaced in Variscan period. The authors use precise dating methods of zircons to identify some of intrusions emplaced in Devonian and Silurian. Zircon SHRIMP U-Pb dating of three intrusions yields apparent ^206Pb/^238U ages of 436 ± 8Ma, 370 ± 7Ma, and 366 ± 8Ma. Meanwhile, petrology and geochemistry studies indicate that the Devonian and Silurian intrusions are similar to active continental margin intrusions. Based on the available data, the authors propose that the oceanic lithosphere of the ancient oceanic basin of current Southern Tianshan had been subducting beneath the Yili-Yisaokehu block from Silurian to early Carboniferous.