Chronology And Geochemistry Of The Mesozoic Volcanic Rocks In Baishilazi Area,Heilongjiang Province

The Baishilazi area is located in Northern Da Hinggan mountains,Mesozoic crust-mantle interaction was strong,the lithosphere was significantly thinned,large scale magmatic activity was frequent,which is an important part of the Circum-Pacific volcanic zone.The Mesozoic volcanic rocks are widely developed in t-his area.The volcanism was generated from Later Triassic to Later Cretaceou-s in this area.This article on the research of geochronology and geochemistry of magmatic rock in this area,discuss the age of igneous rocks,magma source characteristics and tectonic setting,identify characteristics of tectonic-magmatic evolution in the region.The ages of the Mesozoic volcanic rocks in study area are 114-118Ma,with an average around 115Ma,the rocks were formed in the Early Cretaceous.They are a set of aluminum to aluminum high-kalkaline-shoshonite series and consisting mainly of dacite rhyolite intermediate-acid volcanic rocks,generally have the petrochemistry characteristic of high alumina and silicon,alkali-rich,low iron and magnesium;And the volcanic rocks are relatively enriched in light rare earth elements,the fractionation of light rare earth elements is more obvious,the fractionation of heavy rare earth elements is not obvious,the internal fractionation of light rare earth elements than the internal fractionation of heavy rare earth,some form of distribution of heavy rare earth close to the level curve.The value of ?Eu is 0.50-0.90,with an average of 0.76,therefore they have a moderate negative Eu anomaly.The rocks have an enrichment of large ion lithophile(LILE)and a loss of high field strength elements.The initial 87Sr/86Sr ratio is situated between 0.705302-0.709085,the initial 143Nd/144Nd ratio change is extremely small,is restricted in between 0.51263?0.51272,?Nd(t)concentrates between 0.95?2.84.The TDM(t)changes in the range of 615-827 Ma.Different lothological volcanic rocks in study area have an great similarity in evolution characteristics which is crystallization differentiation in magma and crustal contamination having played an important role in the process of evolution.Tectonic setting of volcanic rock formation stretching environment,due to the NWW-SEE regional stretch of the interaction of Izanaqi plate and the Eurasian plate.The magmatic activity is result of the Izanaqi plate subduction under the Eurasia plate since the Late Mesozoic,the magma formed by partial melting of low-melting component(Metasomatized mantle which enriched in water and LEE)of the upper lithosphere mantle due to the asthenosphere mantle upwelling and the geothermal gradient increasing under the background of stretching and thinning of the lithosphere.