雪峰山黔阳地区基性岩锆石SHRIMPU-Pb年龄及意义

Zircon SHRIMP U-Pb Ages of the Mafic Rocks from the Qianyang Region in Xuefengshan and Their Implication

雪峰山中段基性岩锆石SHRIMP U-Pb测年结果表明雪峰山地区存在多期基性岩。在黔阳(安江)地区发现了的晚三叠世和新元古代的基性岩。在所测的三个不同地区的样品中,发现了一些新太古代-古元古代、中元古代、新元古代以及中生代(印支运动)构造热事件信息,但缺少典型Rodinia超大陆聚合信息。早期的基性岩中锆石成分比较复杂,有很多来自基底的捕获锆石,随着时代的变新,来自基底的信息逐渐减少甚至没有。黔阳地区的基性岩及其时代研究表明:(1)桃江-安化-黔阳-溆浦-靖州断裂是雪峰山的中央断裂,它有多期活动历史,并控制了不同阶段的基性-超基性岩的产出;(2)晚三叠世的基性岩在雪峰山中央断裂左行走滑拉分区域形成,不代表裂谷或碰撞后伸展环境;(3)扬子板块东南缘存在新太古代-古元古代基底。

Zircon SHRIMP U-Pb dating results of the mafic rocks from the central Xuefengshan area showed that multi-stage mafic intrusions occurred in the study region. Late Triassic and Neoproterozoic mafic rocks have been reported in the Qianyang region（Anjiang）. Tectonothermal events of the Neoarchean-Paleoproterozoic, Mid-Proterozoic, Neoproterozoic and Mesozoic have been recorded in the samples from three different areas in the Qianyang region, but there is no information concerning the aggregation of the Rodinia Supercontinent. The composition of zircons from the mafic rocks of the early stages are more complicated, many zircon grains were captured from the basement of the Yangtze Plate, however, fewer zircons from the basement have been found in the younger mafic rocks. The occurrence of multi-stage mafic rocks in the Qianyang region shows that（1） the Taojiang-Anhua-Qianyang-Xupu-Jingzhou Fault is the Central Fault Zone in Xuefengshan. It had a long and complex history and controlled the occurrence of the various stages mafic-ultramafic rocks;（2） Late Triassic mafic rocks in the Qianyang region occurred in the pull-apart region of the sinistral Taojiang-Anhua-Qianyang-Xupu-Jingzhou Fault of Xuefengshan, but they were not produced in the rifting valley or the post-collisional extension environment;（3） the Neoarchean-Paleoproterozoic basement may underlie the southeast margin of the Yangtze Plate.