粤东北仁差盆地早侏罗世花岗岩基底LA-ICP-MS锆石U-Pb年龄及其地质意义

摘要

Rencha basin is one of the typical Mesozoic-Cenozoic volcanic fault basins in northeast Guangdong. Drilling exploration reveals that its basement is mainly composed of Paleozoic metamorphic rocks and graphic granite. In order to further investigate the formation age of the basement rock masses and to improve the knowledge of geological evolution of the area, the authors conducted isotope dating of the samples of graphic granite basement from two drill holes in the basin. The 206Pb/238U measured ages of two groups of zircon by LA-ICP-MS are respectively 179 ± 1Ma and 186Ma, suggesting that the formation age of the graphic granite basement of Rencha Volcanic Basin is late Early Jurassic, i.e., Rencha Basin was formed at the first episode of the Yanshanian mag⁃matic activity. These ages not only deepen the understanding of the formation and evolution of the Rencha Basin but also provide new chronologic data for the report that northeast Guangdong was lack of magmatic activity in Early Jurassic.%钻探勘查揭露表明，粤东北仁差盆地基底主要由古生代变质岩和文象花岗岩组成。为进一步查明其基底岩体形成的时代，提高对该地区地质演化的认识，对盆地内2个勘查钻孔内的文象花岗岩岩心取样，进行LA-ICP-MS锆石U-Pb同位素定年，测得谐和年龄为179±1Ma和186Ma。此结果表明，仁差盆地基底文象花岗岩的形成时代为早侏罗世晚期，即其为燕山期第一幕岩浆活动的产物。此年龄不仅加深了对仁差盆地形成演化的认识，也为粤东北地区早侏罗世时期缺乏岩浆岩活动的报道提供了新的年代学资料。