广东南雄断裂带Ar-Ar年龄及其地质意义

The Ar-Ar Age of the Nanxiong Fault Zone in Guangdong Province and Their Geological Significance

南雄断裂带是一条大型的拉伸剥离断层。在详细的野外调查和岩石样品镜下观察的基础上,对南雄断裂带糜棱岩中的同构造变形-变质矿物白云母进行了Ar-Ar法同位素年龄测定。年代学研究结果表明,南雄断裂带作为拉伸剥离正断层活动开始于早白垩世（117.3±2.7 Ma）,而其强烈的伸展变形韧性剪切发生在早白垩世末~晚白垩世初（Ar-Ar坪年龄为94.6±0.4 Ma）,随后在88.9±1.0 Ma和81.1±2.0 Ma还可能发生过2次较明显的热扰动事件。南雄断裂带Ar-Ar年龄数据为进一步判断华南白垩纪岩石圈伸展作用发生的时间提供了新的热年代学制约,即是说,早白垩世末~晚白垩世初是区域岩石圈伸展的重要时期。

The Nanxiong fault zone is a large-scale extension detachment structure.According to the results of Ar-Ar laser step-heating dating of the syntectonic muscovite separated from a mylonite sample in the Nanxiong fault zone,combining with the field surveying and microstructure analysis,the initial extension of the Nanxiong fault zone occurred at 117.3±2.7 Ma in Early Cretaceous.The strong extension and ductile shearing of the fault zone took place at the end of the Early Cretaceous or the beginning of the Late Cretaceous with an Ar-Ar plateau age of 94.6±0.4 Ma.Two obvious late-stage thermal perturbations are revealed with the Ar-Ar ages of 88.9±1.0 Ma and 81.1±2.0 Ma.The Ar-Ar chronology data of the Nanxiong fault zone provide a new geochronological constraint on the Cretaceous lithospheric extension in South China.The transition stage from the Early Cretaceous to the Late Cretaceous is an important epoch of the lithospheric extension in the study.