Research On Xiqiaoshan Volcanic Rocks In Sanshui Basin

Xiqiao Mountain is a famous national scenic spot in the south-central part of Guangdong.It is also one of the two major volcanic eruption centers in the Sanshui Basin of the Cenozoic.Its development process is just at the critical time before the expansion of the South China Sea.Geological activities and even the evolutionary pattern of the South China Sea from rupture to expansion are potentially significant.In the process of participating in the implementation of the National Natural Science Foundation of China,the author conducted on-the-spot exploration and sampling of Xiqiao Mountain.I take the Xiqiaoshan volcanic rock and its geological background were used as independent and specialized research objects for the first time,through chronology and petrography.Comprehensive analysis of geochemical and tectonic settings has achieved the following important insights:Xiqiao Mountain constitutes a complete magma eruption system.In the system,rhyolite and coarse shale coexist and rhyolite accounts for a larger proportion;rhyolite contains high Na and low Na.Xiqiao Mountain is a multi-period volcanic eruption,in which the eruption period of trachyte magma can reach at least 2 times,and the eruption period of rhyolite magma can reach at least 4 times.Their main eruption period is 45Ma-46 Ma.According to the current geological record,Xiqiao Mountain or the entire Sanshui Basin has entered the stage of extension and rupture,and it is the “sacred place” for the first shot of magma eruption.It is also the place where the volcanic activity finally ends.The K-Ar age of rhyolite measured in the Dugang area of Xiqiao Mountain is 28.25 Ma,which provides a valuable opportunity to observe the volcanic response of the land during the expansion of the South China Sea basin.The Xiqiao Mountain has a volcanic-sedimentary composite structure,and the siliceous rocks(meteorites)of pure sedimentary genesis and gas-liquid genesis develop in the parts and parts of the mountain.Although the contemporary Xiqiao Mountain retains geological remnants such as caldera,volcanic passages,and volcanic ash settlements,all geological records indicate that it is a complex mountain formed by many volcanic eruptions and sedimentary depressions,and volcanic rocks occupy in the mountains.Overwhelming advantage.The Xiqiao Mountain not only has a rough trachytic texture,but the rhyolite content of the rhyolite is higher than that of quartz except for the high content of SiO2.Some samples show the characteristics of coarse rock under the microscope.The two types of rocks have strong Eu negative anomalies;they are all enriched with Ta,Nb,Zr,Hf high field strength elements and Rb,Th,U and other large ion lithophile elements,which are consistent with the characteristics of typical continental rift alkaline volcanic rocks.It is derived from the crystallization of basaltic magma in Wuyuan.Among the typical bimodal volcanic rock combinations in the Sanshui Basin,Xiqiao Mountain is dominated by alkaline and acidic rocks.It is not only one of the largest volcanic eruptions in the basin,but also throughout the basin.It is an important window to observe the rift environment of the Sanshui Basin and its response to the early evolution of the South China Sea.