新疆库鲁克塔格地区古生代花岗质侵入岩全岩Sr-Nd和锆石Hf同位素地球化学特征及其意义

白海子南岩体是库鲁克塔格地区典型的古生代花岗质侵入岩。深入了解该岩体岩石成因及物质来源，对研究库鲁克塔格地区构造背景及古生代地壳演化过程具有重要意义。笔者对白海子南岩体进行了系统的全岩Sr-Nd和锆石Hf同位素及锆石微量元素研究。结果表明，该岩体具有中等ISr（0.710 01~0.712 87）比值，富集的εNd（t）值（-21.01~-18.07）和εHf（t）值（-26.55~-17.28），对应的Nd二阶段模式年龄（TDM2）和Hf模式年龄（TDMC）分别为2.60~2.84 Ga和2.43~3.00 Ga，表明其是古元古代早期—新太古代地壳物质再循环的产物。锆石微量元素分析表明，该岩体锆石为壳源岩浆锆石，TZr均值为745℃，TTi均值为692℃，属于“冷”岩浆，岩体形成于主动大陆边缘，是南天山洋向南俯冲到塔里木克拉通之下后期阶段的产物，俯冲过程中幔源岩浆底侵产生的余热为该岩体熔融提供热源。在库鲁克塔格地区发现多期次古生代花岗质侵入岩，这些岩体的εNd（t）值和锆石εHf（t）值随年龄的减小呈现先上升后下降的趋势，结合前人已有资料，推测在南天山洋向塔里木克拉通俯冲过程中，库鲁克塔格地区奥陶纪—早石炭世地壳演化经历了先减薄再加厚的演化过程。

Geochemical Characteristics and Significance of the Whole Rock Sr-Nd and Zircon Hf Isotopic in the Paleozoic Granite-plutons in Kuruktag,Xinjiang

The Baihaizi pluton is typical Paleozoic granitic intrusive rock in Kuruktag area.A deep understanding of the petrogenesis and the source material of the rock is of great significance to the study of the tectonic setting and Paleozoic crustal evolution in this area. This paper studied the whole rock Sr-Nd, zircon Hf isotope and zircon trace elements of the Baihaizi pluton.The isotopic results indicate that the rocks have the intitial medium value of ISr (0.710 01~0.712 87), with the negative εNd(t) (-21.01~-18.07) and negative εHf(t) (-26.55~-17.28) values. The corresponding Nd two stage mode age (TDM2) and Hf mode age (TDMC) range from 2.60 Ga to 2.84 Ga and from 2.43 Ga to 3.00 Ga, respectively, indicating that it is the product of the recycling of crustal materials from the early Paleoproterozoic to the Neoarchean.The zircon trace element analysis shows that the zircons are magmatic crust zircons, with an average TZr=745℃ and TTi=692℃.The "cold" magma formed in the active continental margin and it was the product of the southward subduction of the south Tianshan ocean to the lower part of the Tarim Craton in the late stage. Many Paleozoic granitic intrusive rocks have been found in the Kuruktag area, the εNd(t) value and zircon εHf(t) value increase first and then decrease with a reduction of age.Combined with the previous data, it is held that crustal evolution in the Kuruktag area experienced a thin-to-thick process in the subduction of the south Tianshan ocean to the Tarim block during the Ordovician-Early Carboniferous.