河南商城县汤家坪钼矿辉钼矿铼-锇同位素年龄及地质意义

Re-Os isotopic ages of Tangjiaping molybdenum deposit in Shangcheng County,Henan and their geological significance

为查明商城县汤家坪大型钼矿床形成的时代,建立钼多金属矿成矿模式,利用电感耦合等离子体质谱仪对汤家坪等3个钼矿床的7件辉钼矿样品进行了Re-Os同位素年龄测定,获得汤家坪钼矿床辉钼矿Re-Os等时线年龄为(113.1±7.9)Ma,准确厘定其成矿时代为早白垩世;测得天目沟钼矿床辉钼矿Re-Os同位素模式年龄为(121.6±2.1)Ma,大银尖钼矿床辉钼矿Re-Os同位素模式年龄为(122.1±2.4)Ma,初步确定大别山钼成矿带的成矿年龄大约在(122.1±2.4)～(113.1±7.9)Ma之间。结合前人研究成果,认为大别山北麓钼成矿作用的地球动力学背景为燕山晚期大别造山带在伸展机制下岩石圈减薄,中国中东部区域构造-动力体制由近EW向构造为主向近SN向构造为主的大转换时期。

In order to determine the age of the Tangjiaping large-size molybdenum deposit in Shangcheng County and establish the metallogenic model for molybdenum-polymetallic ore deposits, the authors dated seven molybdenite samples from Tangjiaping and two other molybdenum deposits by using such ionic mass spectrographs as inductance coupling. The results show that the Re-Os isochron age of molybdenite from the Tangjiaping molybdenum deposit is （113.1±7.9） Ma, suggesting Early Cretaceous, the Re-Os isotopic model age of molybdenite from the Tianmugou molybdenite is （121.6 ±2.1）Ma, and the Re-Os isotopic model age of molybdenite from the Dayinjian molybdenum is （122.1 ± 2.4）Ma. It is thus thought that the ore-forming age of the Dabie molybedum metallogenic belt should be （ 122.1 ±2.4） - （ 113.1 ± 7.9） Ma. Considering also the achievements made by previous workers, the authors hold that the molybdenum metallogenic geodynamic background of the northern slope of the Dabie Mountain should be a great transformation period during which the lithosphere of the Dabie orogenic belt became thinner under the stretching mechanism and the regional tectonic-dynamic system of central and eastern China turned from nearly EW-trending to nearly SN-trending structures.