摘要
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 Ma)。玄武岩和玄武质安山岩多以岩脉产出,年龄在435～300 Ma之间,正的ε_(Hf)(t)(+0.7～+15.4)值,这意味着东准噶尔为年轻地壳控制,前寒武纪基底即便存在也非常有限。白碱沟地区侵入的正长斑岩锆石U-Pb年龄为307 Ma和315 Ma,正的ε_(Hf)(t)值,表明地壳物质的垂向增生。该区流纹岩锆石U-Pb年龄为323 Ma和315 Ma,也有正的ε_(Hf)(t)值,表明地壳物质的侧向增生。帐篷沟地区角斑岩和流纹岩锆石U-Pb年龄分别为336 Ma和332 Ma,其形成于火山弧或受到了部分岛弧物质混染的环境中。因此,在后碰撞伸展垮塌背景下,东准噶尔主要为俯冲增生地体,现今可定义为古生代马里亚纳型洋内岛弧。
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）. Basahs and basaltic andesites are more likely output as dikes, and they display age-range from 435 Ma to 300 Ma and show positive nf（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 6.f （t） values in Late Carboniferous（307 Ma and 315 Ma）indicate a vertical accretion of crustal materials. The Baijiangou rhyolites which show positive 8Hf（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.
出处
《地质科学》
CAS
CSCD
北大核心
2012年第4期955-979,共25页
Chinese Journal of Geology(Scientia Geologica Sinica)
基金
国家科技重大专项"准噶尔盆地深层火山岩储集体形成演化与分布预测"(编号:2011ZX05008-003-40)资助
关键词
中亚造山带
东准噶尔
锆石U-Pb定年
Hf同位素
年轻地壳
岛弧
陆壳增生
Central Asian orogenic belt,East Junggar,Zircon U-Pb dating, Hf isotopic,Juvenile crust, Island arc, Continental growth
