新疆东准噶尔卡拉麦里蛇绿岩的形成和侵位时限——来自辉绿岩和凝灰岩LA-ICP-MS锆石U-Pb年龄的证据

新疆东准噶尔卡拉麦里蛇绿岩是中亚造山带中最具代表性的蛇绿岩之一,其所代表的古洋盆的形成和关闭时限一直受到地学界的密切关注。采用LA-ICP-MS锆石U-Th-Pb同位素方法,获得卡拉麦里蛇绿岩中辉绿岩的年龄为416.7Ma±3.2Ma,代表了卡拉麦里蛇绿岩的形成年龄。不整合于蛇绿岩之上的地层凝灰岩的年龄为343.0Ma±5.0Ma,限定了卡拉麦里蛇绿岩侵位时代的上限,同时也为沉积盖层提供了可靠的年龄依据。即卡拉麦里蛇绿岩所代表的古大洋形成于早泥盆世洛霍考夫期,闭合于早石炭世杜内期前。卡拉麦里蛇绿岩形成和侵位时代的准确限定对研究东准噶尔的构造演化和古生代中亚地区构造格局提供了重要的制约。

Formation and emplacement age of Karamaili ophiolite：LA-ICP-MS zircon U-Pb age evidence from the diabase and tuff in eastern Junggar,Xinjiang

The Karamaili ophiolite is one of the representative ophiolites in the Central Asian Orogenic Belt（CAOB）.The time limits of the opening and closure of the Karamaili oceanic basin remain a key problem due to the lack of high accuracy isotopic ages.The LA-ICP-MS zircon U-Th-Pb dating of diabase in Karamaili ophiolite yielded an age of 416.7±3.2 Ma,recording the generation of the oceanic crust.Sedimentary rocks conformably overlies Karamaili ophiolite.The 343.0±5.0Ma zircon U-Pb age from the tuff overlying the strata constrains the upper limit of the emplacement age of the Karamaili ophiolite and suggests that the sedimentary cover is Early Carboniferous in age.Therefore these ages indicate that the Karamaili oceanic basin was opened in the Lochkovian stage during Early Devonian and closed before the Tourmaisian stage during Late Carboniferous.Accurate constraints on the formation and emplacement age of Karamaili ophiolite provide important constraints for the tectonic evolution of the eastern Junggar Orogenic Belt and the tectonic framework of the CAOB during the Palezoic period.