珠江口盆地白云凹陷渐新世/中新世地质事件的碎屑组分响应

摘要

The source areas changed obviously during Oligocene/Miocene in the northern South China Sea.With the point-counting method of thin sections of Miocene Zhujiang Formation and Oligocene Zhuhai Formation in Baiyun Sag, Pearl River Mouth Basin, the characteristics of detrital components were studied in detail.The results show that: the lithic fragments in Zhuhai Formation were dominated by plutonic magmatic fragments, and there were also many feldspar and sedimentary lithic fragments, in agreement with the fact that the source was mainly from Mesozoic granite rock in the South China; in contrast, the lithic fragments were dominated by metamorphic fragments in Zhujiang Formation, and there were some magmatic fragments, sedimentary fragments and more feldspar, indicating more supply of the sources in Zhujiang Formation.With the various Oligocene/Miocene geological events, especially accompanied by weathering and increasing erosion caused by the uplift of Qinghai-Tibet Plateau, the source areas expanded within the ancient South China land and even to eastern Tibetan Plateau.The change of clastic components was the result of these various geological events.%南海北部渐新世/中新世之交发生了物源突变地质事件.利用珠江口盆地白云凹陷渐新统珠海组和中新统珠江组砂岩薄片镜下计点法统计技术,详细研究了碎屑组分的变化特征.结果表明:珠海组砂岩碎屑组分中,岩屑以深成的岩浆岩屑占绝对优势,长石和沉积岩屑含量也相对较高,与该期物源主要来自华南沿海近源以燕山期花岗岩为主的母岩区相一致;而珠江组砂岩中,岩屑以变质岩屑占优势,同时也含有一定量的岩浆岩屑、沉积岩屑和较多的长石,显示珠江组具有更多的物源供给区.随着渐新世/中新世之交各种地质事件发生,尤其是伴随青藏高原隆升引起的大陆风化及侵蚀程度增强,珠江口盆地沉积物源区向华南古陆内部古老的沉积-变质岩区和青藏高原东麓扩展,碎屑组分变化应该是该期各种地质事件的综合作用结果.