Zircon age and occurrence of the Adaatsag ophiolite and Muron shear zone, central Mongolia: constraints on the evolution of the Mongol–Okhotsk ocean, suture and orogen
Zircon age and occurrence of the Adaatsag ophiolite and Muron shear zone, central Mongolia: constraints on the evolution of the Mongol–Okhotsk ocean, suture and orogen
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DOI：
10.1144/0016-764903-146
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发表时间：
2005-01
影响因子：
2.7
通讯作者：
O. Tomurtogoo;B. Windley;A. Kröner;G. Badarch;Dunyi Liu
中科院分区：
文献类型：
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作者：
O. Tomurtogoo;B. Windley;A. Kröner;G. Badarch;Dunyi Liu
蒙古东部的阿达察格蛇绿岩位于蒙古-鄂霍次克缝合带，该缝合带从蒙古中部穿过外贝加尔湖延伸到鄂霍次克海，并将西伯利亚板块和阿穆尔（蒙古）板块分开。蛇绿岩序列从蛇纹岩混杂岩和蛇纹化纯橄榄岩和方辉橄榄岩向上穿过层状辉长岩（含淡色辉长岩伟晶岩脉）、韦尔岩和单斜辉石岩，到达各向同性辉长岩和淡色辉长岩、席状镁铁质岩脉和富含橄榄石的玄武质熔岩，其上覆红色燧石和变碎屑沉积物。一条淡色辉长岩伟晶岩脉的单颗粒锆石207 Pb/206 Pb蒸发年龄为325.4 ± 1.1Ma，记录了该深成岩套的岩浆结晶时间，从而记录了蛇绿岩形成的蒙古-鄂霍次克洋洋壳的形成时间。对一个糜棱岩化花岗岩的U-Pb二次电离质谱（西姆斯）和蒸发锆石年龄为172 Ma，提供了发生在蒙古-鄂霍次克缝合带左侧的Muron剪切带的最大年龄，表明蒙古东部缝合带至少形成于中侏罗世。我们回顾了俯冲构造的证据和模型，俯冲构造引起了主要的钙碱性岩基沿着活跃的大陆边缘的接壤板块和广泛的，后碰撞，碱性过碱性岩浆活动。虽然造山带的岩浆历史比较清楚，但海洋的年龄以及缝合带的形成和变形时间却不清楚。我们关于阿达察格蛇绿岩和穆龙剪切带的新数据为蒙古-鄂霍次克海洋和造山带的早期和晚期发展提供了关键制约因素。
The Adaatsag ophiolite in eastern Mongolia is situated in the Mongol–Okhotsk suture zone, which extends from central Mongolia through Transbaikalia to the Sea of Okhotsk and separates the Siberian and Amurian (Mongolian) plates. The ophiolite sequence passes upwards from serpentinite mélange and serpentinized dunite and harzburgite, through layered gabbro (with leucogabbro pegmatite dykes), wehrlite and clinopyroxenite, to isotropic gabbro and leucogabbro, sheeted mafic dykes, and olivine-rich basaltic lavas, overlain by red chert and meta-clastic sediments. A single-zircon mean 207Pb/206Pb evaporation age of 325.4 ± 1.1 Ma for a leucogabbro pegmatite dyke records the time of igneous crystallization of the plutonic suite, and thus the time of formation of oceanic crust in the Mongol–Okhotsk ocean that gave rise to the ophiolite. A U–Pb secondary ionization mass spectrometry (SIMS) and evaporation zircon age of 172 Ma for a mylonitized granite provides a maximum age for the left-lateral Muron shear zone, which occurs close to the left-lateral Mongol–Okhotsk suture, and indicates that the suture in eastern Mongolia formed at least by the mid-Jurassic. We review the evidence and models for subduction tectonics that gave rise to major calc-alkaline batholiths along active continental margins of the bordering plates and to extensive, post-collisional, alkaline to peralkaline magmatism. Whereas the magmatic history of the orogen is better known, the age of the ocean, and the time of formation and deformation of the suture zone are not. Our new data on the Adaatsag ophiolite and Muron shear zone provide key constraints on the early and late stages of development of the Mongol–Okhotsk ocean and orogen.