伊犁果子沟地区新元古代冰成沉积的碎屑锆石LA-ICP-MS U-Pb年龄及其地质意义

为了对新疆果子沟地区塔里萨依组冰成沉积进行时代限定及前寒武纪地质演化讨论,开展了碎屑锆石LA-ICP-MS U-Pb定年工作。碎屑锆石最年轻年龄介于620~610 Ma和580~572 Ma之间,表明塔里萨依组冰成杂砾岩代表了埃迪卡拉纪时期的产物,而且在一次大冰期中发生了2次的小冰期旋回,同库鲁克塔格地区的汉格尔乔克组冰碛砾岩对应。碎屑锆石年龄谱没有反映出1000~700 Ma的年龄分布,但这个年龄段相关的岩浆活动在伊犁以北至温泉地区被广泛发现。而在年龄谱中大量存在的650~600 Ma年龄,本区附近却没有相关岩浆活动记录的报道,结合本区同库鲁克塔格地区新元古代冰期沉积存在的相似性,说明塔里萨依组冰期沉积物可能接收了更远的"伊犁块体"以南地区的物源。同时探讨了650~600 Ma岩浆活动可能与"伊犁块体"同塔里木板块分离,向哈萨克斯坦板块聚合有关。

LA-ICP-MS U-Pb Dating of Detrital Zircons from Neoproterozoic Glacial Sediments in Guozigou Area, Ili and Its Geological Implication

There is one unit of Neoproterozoic glacial sediment-Talisayi Formation outcrops in Guozigou area, which is located in the north of Ili and south of Sailimu Lake. LA-ICP-MS U-Pb dating works of detrital zircon were carried out in order to identify the glaciation age and the Precambrian geological evolution. Several younger ages are 620~610 Ma and 580~572 Ma, which indicates the glaciation happened in Ediacaran period, and contained two glacial cycles. The Talisayi Formation correlated with Hangelchaok diamictites in Quruqtagh area. There is no age from 1000 Ma to 700 Ma recorded in detrital zircons, but lots of ages from 650~600 Ma. The ages suggest that the provenance of the glacigenic sediments was from the south of Yili. The tectonic events during 650~600 Ma correlated with the ending of breakup from Tarim and the beginning of assemblage to Kazakhstan.