Petrological Characteristics And Tectonic Setting Of The Igneous Rocks In Mesozoic From Maoming Basin Of Guangdong Province

Based on the previous research in Maoming,this paper makes a further study for the Yanshanian volcanic and intrusive rocks.The magma intrusion activity is mainly occurred at Cretaceous,it belongs to the product of the third phase of the yanshanian magmatic activity.The intrusive rocks are biotite granite and two-mica granite,they belong to aluminum-weakly peraluminous and subalkalic series and show characteristics of high silicon and rich potassium.The rocks are aluminous-peraluminous S-type granite.The REE patterns show right-dip type,negative Eu anomaly,enrichment of Rb,Th,K and depletion of Ta,Nb,Ti.The granite was the product of partial melting of the crust and it was affected by the subduction of the Pacific plate.In this area,the volcanism began in the late Cretaceous,it was the product of the late Yanshanian magmatic activity,and the volcanic rocks distributed as a lava flow.The volcanic rock samples comprise rhyolites and felsites,showing characteristics of high silicon and rich potassium;they are mainly fall in the field of shoshonite and high-K calc-alkaline in the diagram;According to the result of trace element and REE,the REE patterns and trace element spider diagrams were plotted after normalization.The chondrite-normalized REE patterns show enrichment of LREE,a downward trend from left to right,negative Eu anomaly and flat HREE characteristics.The primitive-normalized trace elements spider diagrams show enrichment of K,Rb,Th,U and depletion of P,Ti,Nb,Ta,implying their crustal source;The initial value of Sr is between the mean values of the continental crust and the mantle.Based on the rock types,petrologic characteristics and the distribution of trace elements,we confirm that the volcanic rocks are the product of plate subduction.In Early Cretaceous,the Yunkai Block was affected by the Pacific plate and Eurasian plate,melting of the continental crust formed the calcalkaline granite.In Late Cretaceous,in the decompressive plate subduction and back-arc extensional environment,the magma was derived from partial melting of Proterozoic basement,the the magma ascended and formed the high silicon and rich potassium rhyolite.