江南造山带东段赣东北蛇绿岩的形成时代:来自辉长岩LA-ICP-MS锆石U-Pb年龄的证据

摘要

赣东北元古宙蛇绿岩位于江南造山带东段,主要由蛇纹石化超基性岩、堆晶岩、辉长岩、辉绿岩、低温高压蓝片岩以及斜长花岗岩组成.对赣东北蛇绿岩中辉长岩进行了LA-ICP-MS锆石U-Pb定年,获得207 pb/206 Pb加权平均年龄值为(992 ±25) Ma(MSWD=1.19),以此代表该辉长岩的结晶年龄.这一年代学结果表明扬子陆块东南缘古洋盆在新元古代早期就已存在,但晚于扬子北缘中元古代晚期古洋盆(～1 120 Ma),暗示扬子克拉通中一新元古代结晶基底的形成具有从西北往东南逐步拼贴的特征.%Proterozoic Ophiolite of the eastern Jiangnan orogenic belt in Northeastern Jiangxi was mainly composed of serpentinized ultramafic rock,cumulated rock,isotropic gabbro and diabase,low-temperature and high-pressure blueschist and plagiogranite.LA-ICP-MS zircon U-Pb dating for one gabbro sample from the Northeastern Jiangxi Ophiolite yielded a 207pb/206pb age of (992 ± 25) Ma (MSWD =1.19),which represented the intrusion time of the gabbro.The geochronological result suggests the existence of Early Proterozoic palaeooceanic basin in the southeastern Yangtze block,which is younger than the late Meso-Proterozoic oceanic basin in the northern margin of the Yangtze block.Therefore,it is proposed that the Meso-Neoproterozoic crystallization basement rocks in the Yangtze craton were formed in a gradually aggregated process with characteristics of trending from northwest to southeast direction.