西藏龙马拉Cu-Fe-Pb-Zn多金属矿床金云母Ar-Ar定年及其地球动力学意义

冈底斯北缘Pb-Zn-Ag-Cu-Fe多金属成矿带内发育有大量的矽卡岩矿床。本文研究的龙马拉矿床便是位于该成矿带东侧典型的层控式矽卡岩型Cu-Fe-Pb-Zn多金属矿床。对矿床成矿时代的精确厘定,是理解矿床成因机制和冈底斯北缘大规模矽卡岩型成矿地质背景的关键。本文首先对龙马拉矿床中与磁铁矿共生的蚀变云母进行了电子探针分析,结果显示这些云母为金云母;金云母的Ar-Ar同位素测年显示,其Ar-Ar坪年龄为56.32±0.48 Ma,等时线年龄为55.58±0.93 Ma。根据金云母与矿石矿物的共生关系可知,该年龄应代表龙马拉多金属矿床的成矿时代。综合前人的研究结果,认为龙马拉多金属矿床形成于印-亚陆陆碰撞的主碰撞汇聚成矿阶段,新特提斯洋壳板片的回卷很可能是该矿床形成的深部动力学机制。

Ar-Ar age of phlogopite from the Longmala copper-iron-lead-zinc deposit in Tibet and its geodynamic significance

The north Gangdise Pb-Zn-Ag-Cu-Fe belt is one of the most important metallogenic belt in the Tibetan collisional orogenic belt. The Longmala deposit is located in the eastern part of the Gangdise metallogenic belt. Constraining the timing of mineralization of this deposit is crucial to the better understanding of the genesis of the deposit and the deep geodynamic processes which controlled the large-scale mineralization of this area. The electron microprobe analyses reveal that the altered mica is phlogopite. This paper presents the Ar-Ar dating results for magnetite mineralization conducted on phlogopites collected from the Longmala deposit. Phlogopite from the Longmala deposit yielded a well-defined ⁴⁰Ar/³⁹Ar plateau age of 56.32±0.48 Ma and an isochron age of 55.58±0.93 Ma. These ages suggest that the Longmala deposit was developed in the period of main collisional orogenic setting in Tibetan orogenic belt. Combined with the former research and the data of regional geology, the authors hold that the deep geodynamic process which controlled the formation of this deposit was the rollback of the Neo-Tethys slab.