新疆北部富蕴县埃达克岩的同位素年代学及其对古亚洲洋板块俯冲时限的制约

Geochronology of the Fuyun adakite,north Xinjiang and its constraint to the initiation of the Paleo-Asian Ocean subduction.

采用 LA-ICP-MS 锆石 U-Ph 同位素定年方法对分布于新疆北部富蕴县托让格库都克组中的埃达克岩进行了年代学研究。结果表明,以往被认为属早泥盆世的埃达克岩的形成年龄为441.3±1.8Ma,属早志留世。由于托让格库都克组中的埃达克岩被认为是由新生的古亚洲洋板块俯冲后部分熔融形成的,因此,埃达克岩的同位素年代学研究结果表明,新疆北部东准噶尔地区古亚洲洋的板块俯冲从早志留世就已经开始。这是首次采用精确的同位素定年手段确定的古亚洲洋板块俯冲作用开始的时间,具有十分重要的地质意义。

Zircon LA-ICP-MS U-Pb dating of the Fuyun adakites of Tuoranggekuduke Group, north Xinjiang has been carried out in this study. The Tuoranggekuduke Group was previously considered to be early Devonian. Our result indicates that the zircon U-Pb age of the Fuyun adakites is 441.3 ± 1.8Ma. They might be formed at early Silurian. Previous studies suggest that the formation of the adakites approximately represents the beginning of oceanic crust subduction. Since the Fuyun adakites were suggested to be derived from the partial melting of the newly subducted Paleo-Asian Oceanic crust, our result indicates that the initiation of the Paleo-Asian Ocean subduction in north Xinjiang occurred at early Silurian. This is the first accurately isotopic age for the initiation of the Paleo- Asian Ocean subduction.