东准噶尔西缘晚古生代火山岩的锆石U-Pb年龄和Hf同位素特征及构造意义

白碱沟和帐篷沟剖面位于东准噶尔西缘,出露有大量古生代火山岩,是研究东准噶尔古生代火山岩及构造演化的有利区域.本文利用LA-MC-ICP-MS锆石U-Pb定年法和Hf同位素系统对该区中的玄武岩、玄武质安山岩、流纹岩、角斑岩以及少量的凝灰岩和正长斑岩进行了地质年代学研究,认为它们形成于早泥盆世至晚石炭世之间(400～307...

Zircon U-Pb age and Hf isotopic systematics of Late Paleozoic volcanic from the western margin of east Junggar and tectonic implication

Two sections,namely Baijiangou and Zhangpenggo,in the western margin of east Junggar,where expose a large number of Paleozoic volcanic rocks,are the favorable areas to study the tectonic evolution of the east Junggar.LA-MC-ICP-MS zircon U-Pb dating and Hf isotopic systematics study of igneous rocks(basalt,basaltic andesite,rhyolite and keratophyre with minor tuff and syenite-porphyry),using geochrony technology,suggests that they were formed during Early Devonian to Late Carboniferous(400～307 Ma).Basalts and basaltic andesites are more likely output as dikes,and they display age-range from 435 Ma to 300 Ma and show positive ε_Hf(t) values(+0.7～+15.4),which suggests that the east Junggar terrane is controled by juvenile crust and that the Precambrian crystalline rocks must be very limited,if there is any.The Zhangpenggou rhyolite and keratophyre,zircon U-Pb ages of 332 Ma and 336 Ma respectively,were formed in a volcanic arc environment or a environment which was mixed with part of island arc.The Baijiangou syenite-porphyries with positive ε_Hf(t) values in Late Carboniferous(307 Ma and 315 Ma)indicate a vertical accretion of crustal materials.The Baijiangou rhyolites which show positive ε_Hf(t)values and zircon U-Pb ages of 315 Ma and 323 Ma suggests a lateral accretion of crustal materials.Therefore,the east Junggar is mainly accretionary prism undering extensional settings of post-collisional period,and it's considered today to be a Paleozoic Mariana-type intra-oceanic island arc.