再论塔里木北缘阿克苏蓝片岩的时代和成因环境:来自锆石U-Pb年龄、Hf同位素的新证据

Revisit to time and tectonic environment of the Aksu blueschist terrane in northern Tarim,NW China: New evidence from zircon U-Pb age and Hf isotope

阿克苏蓝片岩和基性岩墙形成时代和构造背景对认识塔里木地块前寒武纪构造演化以及新元古代超大陆重建具有重要意义。本文通过对含蓝片岩的阿克苏群中变质碎屑岩和侵入阿克苏群的基性岩墙的锆石U-Pb定年及Hf同位素分析表明,（长石）石英片岩中碎屑锆石出现2个明显的统计峰值,较老一组锆石207Pb/206Pb的表面年龄集中在~1.9Ga,并有少量太古代的年龄信息;另一组较年轻锆石206Pb/238U表面年龄峰值为~820Ma,代表阿克苏群的最大沉积年龄。侵入阿克苏群的基性岩墙锆石U-Pb年龄为~760Ma。阿克苏蓝片岩相变质的时间被严格限定在820~760Ma区间内。碎屑锆石Hf同位素地壳模式年龄峰值出现在2.2~2.3Ga,2.6Ga和3.2~3.3Ga。综合本次工作及前人研究成果,表明阿克苏蓝片岩地体是塔里木早前寒武纪基底之上发育起来的大陆边缘岩浆弧。

It is of significant importance to understand the Precambrian tectonic evolution and reconstruction of the Neoproterozoic supercontinent of Tarim block in northwestern China by the study of the timing and tectonic background of the Aksu blueschist and the mafic dyke swarms intruding it. In this study,we carry out U-Pb dating and Hf isotope analysis on zircons from both the meta-clastic rocks of the Aksu blueschist and the mafic dyke swarms. There are two significant age peaks in the U-Pb age spectra of the detrital zircons from the schist,i. e.,the older zircon group concentrates at ~ 1. 9Ga,with minor Archaean component; another group peaking at ~ 820 Ma and representing the oldest deposit time of the Aksu blueschist. The mafic dyke swarms intruding the Aksu blueschist yields a zircon U-Pb age of ~ 760 Ma. Hence,the time of the Aksu blueschist facies metamorphism can be quite precisely defined in the range of 820 ~ 760 Ma. The peaks of the detrital zircon Hf crust-model age spectra appears at 2. 2 ~ 2. 3Ga,2. 6Ga and 3. 2 ~3. 3Ga respectively,implying that Aksu blueschist terrane may be continental margin magmatic arc developed on the Early Precambrian Tarim basement.