闽东古田西朝钼矿床成岩成矿年龄的厘定及其地质意义

Determination of rock-forming and ore-forming ages of the Xichao molybdenum ore deposit in Gutian, eastern Fujian Province, and its geological significance

西朝钼矿是近年来在闽东地区新发现的中型斑岩型钼矿床。通过LA-ICP-MS锆石U-Pb定年及辉钼矿Re-Os等时线定年,获得与成矿密切相关的黑云母二长花岗岩锆石U-Pb年龄为115±1.2 Ma(MSWD=0.90),辉钼矿187 Re-187 Os模式年龄加权平均值为112.6±0.7 Ma(MSWD=0.82),187 Re-187 Os同位素等时线年龄为113.4±0.9 Ma(MSWD=0.11),成岩、成矿年龄基本一致,成矿稍晚于成岩,二者均为早白垩世晚期岩浆-成矿作用的产物。根据辉钼矿Re含量特征,认为西朝钼矿成矿物质为深部壳幔混合来源。西朝钼矿形成于古太平洋板块向欧亚板块持续俯冲下的伸展构造环境,是岩石圈减薄、局部软流圈物质上涌导致下地壳部分熔融形成的产物。

The middle-scale Xichao molybdenum ore deposit was a newly discovered porphyry deposit in eastern Fujian Province.The LA-ICP-MS zircons U-Pb dating of biotite adamellite and molybdenite Re-Os isochron dating yielded a U-Pb age of 115±1.2 Ma(MSWD=0.90)for biotite adamellite closely related to mineralizaiton,and a weighted average 187 Re-187 Os mode age of 112.6±0.7 Ma(MSWD=0.82)for molybdenite,with a 187 Re-187 Os isochron age of 113.4±0.9 Ma(MSWD=0.11).Basicaly same rock-and ore-forming ages,maybe with the former later than the latter,were products of late Early Cretaceous magma-mineralization.The characteristic of Re content in the molybdenum suggests that ore-forming material of Xichao molybdenite deposit originated from deep crust-mantle mixing.The Xichao molybdenum deposit probably formed in an extensional setting due to continuous subduction of Paleo-Pacific plate toward Eurasian continent,i.e.lithospheric thinning process,and may be the product of partial melting of lower crust material caused by uprising and heating of local asthenosphere.