新疆富蕴县希勒库都克岩体锆石U-Pb定年、地球化学和Hf同位素特征及其意义

Zircon U-Pb geochronology,geochemistry and Hf isotopes of the Xilekuduk granite in Fuyun County,Xinjiang,and their significance

在阿尔泰地体与萨吾尔地体之间的额尔齐斯碰撞带之南侧发现了希勒库都克岩体具侵位与穿切变形带的特征,为后碰撞岩体。该岩体二长花岗岩属弱过铝质高钾钙碱性I型花岗岩,稀土配分模式呈明显右倾、轻稀土富集型,基本无铈异常,无铕异常或弱的正铕异常,富集Rb、Ba、U、K、La、Pb、Sr等元素,而相对亏损Th、Nb、Ta、Ti和P元素,岩石具有后碰撞的地球化学特征,表明希勒库都克岩体形成于后碰撞环境。岩石的锆石U-Pb年龄为324Ma,因此将东准噶尔北部地区进入后碰撞阶段的时限约束到了324Ma。希勒库都克岩体的二长花岗岩具有较高的176 Hf/177 Hf平均值(0.283010±0.000019)、εHf(t)值(10.1~14.7,平均12.8),表明形成希勒库都克岩体的后碰撞岩浆可能主要来自于早古生代新生洋壳的部分熔融。

The Xilekuduk pluton,located on south side of the Irtysh collision belt between Altay terrain and Sawuer terrain,invading through deformation zone,has the characteristics of post-collisional granite.The monzonitic granites from the Xilekuduk pluton are high-K,calc-alkalic and weakly peraluminous＂I＂-type granites,with the REE distribution patterns of obviously rightward declining and LREE-enriched,without Ce anomaly,without or with weakly positive Eu anomaly.These rocks have the geochemical signatures of post-collisional granites,enrichment in Rb,Ba,U,K,La,Pb,Sr,and depletion in Th,Nb,Ta,Ti,P,suggesting that the Xilekuduk pluton might be formed in post-collisional setting.The zircons＇ U-Pb age of the monzonitic granites from the pluton is 324 Ma,so the earliest time for the northern area in East Junggar entering post-collisional period was restrained at 324 Ma.Higher176 Hf/177 Hf ratio（average 0.283010±0.000019）andεHf（t）values（10.1to 14.7,average 12.8）,suggesting that the granites might derived from partial melting of the Early Paleozoic new formed oceanic crust.