海南石碌铁矿床花岗闪长斑石岩的锆石LA-ICP-MS U-Pb定年及地质意义

摘要

The Shilu iron ore deposit, located in Hainan Province, is the biggest rich iron deposit in China. The genesis of the deposit is actively debated, some argue that besides the main stage mineralization of volcanic-sedimentary metamorphism, the late stage tectonic-magmatic events might have played very important role in reforming and enrichment of the ores. Many chronological studies on iron ores, Shilu Group (host rocks) and granitoid rocks around the mine have been done, but there are little chronological data about the granite porphyry in the Shilu mine. CL images of the analyzed zircons from the granodiorite porphyry are characterized by well-developed oscillatory zoning, showing these zircons are magmatic zircons. LA-ICP-MS U-Pb dating of the zircons from the granodiorite porphyry in the Shilu mine suggests that the porphyry was intruded in (93 ± 2) Ma. Considering the extensional tectonic environment of South China in Late Yanshanian and geological characteristics in the Shilu mine, we suggest the emplacement of the granite porphyry resulted in the reworking and superimposition on the Shilu iron ore deposit.%海南石碌铁矿床是我国最大的富铁矿矿床,其矿床成因一直存在着争论,其中争议之一是矿床成因除与火山-沉积变质有关外,是否还与后期构造-岩浆事件的改造富集作用有关.前人曾对石碌铁矿床铁矿石、主要赋矿围岩石碌群以及矿区周围出露的花岗岩类进行过多方法同位素地质定年,但迄今尚未对矿区内分布的花岗斑岩类进行相应的工作.本文采用激光剥蚀电感耦合等离子质谱仪(LA-ICP-MS)对矿区内花岗闪长斑岩进行了锆石U-Pb定年,获得了(93±2)Ma的年龄,表明该花岗斑岩侵入时代为燕山晚期晚白垩世.结合燕山晚期华南处于拉张构造环境的认识以及石碌矿区矿床地质特征,暗示晚白垩世拉张事件使石碌矿区内的断裂重新活动从而引起花岗斑岩侵位,而花岗斑岩后期演化的热液对石碌铁矿床的富化具有改造叠加作用.