广东三水盆地始新世火山岩地球化学特征

Geochemistry Characteristics of Eocene Volcanic Rocks in Sanshui Basin,Guangdong

广东三水盆地的演化伴随着强烈的火山活动.为研究三水盆地各类岩石之间的演化关系,对在盆地内的玄武岩、粗面岩和流纹岩样品进行常量、微量元素地球化学分析.对样品的地球化学投图表明:玄武岩样品表现为轻稀土富集的板内玄武岩稀土配分模式,而其微量元素也具有Nb、Ti富集、Sr弱亏损的特征,由部分熔融产生;粗面岩与流纹岩样品稀土与微量元素配分模式相似,两类岩石均经历以斜长石为主的分离结晶过程.华南陆缘在始新世早期处于与红海相似的大陆裂谷环境,喷发来源于深部软流圈地幔的岩浆,但在42Ma之后,火山活动因区域挤压作用而停止.其后的南海扩张可能是两种作用的叠加影响的结果.

Guangdong Sanshui basin developed with extreme volcanic activities.Eruptions from Paleocene to Eocene were con-centrated on Xinzhuang,Buxin,Baoyue and Huayong formations.For research of the relationship between various kind of rocks,geochemistry analyses such as multi-element and rare-earth element determination were launched on basalt,trachyte and rhyolite samples from the research area.Geochemistry diagrams suggest that：REE distribution of basalt followed as mid-plate alkali basalt mode,while their trace element spider diagrams act as continental alkali basalt with Nb,Ti rich and Sr loss.REE distributions of trachyte and rhyolite are similar,which indicate the same crystallization separation process.S-B diagram and pearce diagram show that：granites were partially melted from source region,while trachyte in ZMY and rhyolite in LBS originated from the same source region,and occurred with the process of crystallization separation with plagioclase adventage.Southeast China performed continental rift environment as Red Sea,and its magma may came from lithospheric mantle source.The magmatic activities suspended after 42Ma because of regional extrusion,while breaking up of South China Sea（SCS）later may be a mixed effect of two functions.