柴北缘—东昆仑地区造山型金矿床的Ar-Ar测年及其地质意义

Ar-Ar dating of orogenic gold deposits in northern margin of Qaidam and East Kunlun Mountains and its geological significance

通过对柴北缘—东昆仑地区一批金矿床中绢云母的Ar_Ar测年,确定金矿床形成于晚加里东期和晚华力西—印支期,是该区加里东和晚华力西—印支复合造山过程的产物,是典型的造山型金矿床。金成矿作用主要发生在碰撞造山过程的晚期,金成矿与柴北缘—东昆仑地区的复合造山作用在时空上的“构造迁移”相一致。

The region of northern Qaidam margin and East Kunlun Mountains, located in western Qinghai Province, is a typical multiple orogenic belt in western China. The multiple orogenic belt originally consisted of three microplates (Oulongbuluke, Qaidam and Central Kunlun) together with some micro-oceans and/or aulacogens of different stages located respectively on the southern and northern sides of the microplates. During Early Paleozoic, North Qaidam, North Kunlun and South Kunlun extended into aulacogens and/or micro-oceans, which were closed at the end of Caledonian stage due to their soft collision with the contiguous microplates. The microplates were combined with Eurasia into one body in Late Paleozoic and shifted northward. Meanwhile the southern side of these microplates developed into the Animaqing Carboniferous-Permian micro-ocean belonging to Paleo-Tethys, which was closed during Middle-Late Permian. Early-Middle Triassic foreland deposits were formed on the southern side of the microplates, and Late Variscan-Indosinian collisional granite and large-scale shear zones were produced in the inner part of the microplates. At the same time, the sea/ocean shifted southward and Lower Triassic deposits of passive continental margin were developed in northern Bayan Har on the southernmost side of the region, which experienced collision and orogenic movement during Middle-Late Triassic. Thirteen orogenic gold deposits were discovered in the region of northern Qaidam margin and East Kunlun Mountains, all of which were formed in the multiple orogenic movement. Sericite samples selected from gold ores of six representative gold deposits were used to conduct Ar-Ar dating, and their ore-forming ages are as follows: (425.5±2.1) Ma (Saibagou), (409.4±2.3) Ma (Qinglonggou), (284.04±2.95) Ma (Tanjianshan), (246±3) Ma (Yeluotuoquan), (236.5±0.5) Ma (Wulonggou), and (218.6±3.2) Ma (Dachang). These age data show that the gold deposits were formed in late Early Paleozoic and late Late Paleozoic-Triassic and were products of the multiple orogeny in the region during Caledonian and Late Variscan-Yindosinian. They belong to typical orogenic gold deposits and were mainly formed in the late stage of collisional orogeny. The gradual decrease in ages of the deposits from north to south is coincident with the spatial-temporal tectonic shift of the multiple orogeny in this region.