Huanggangliang Volcanic-extrusive Uplift In The Southern Great Xing'an Range: Discussion On Genetic Relation Between Different Lithofacies And Tectonic Setting Of Formation

The purpose of this paper is to discuss the genetic relation between different lithofacies and the tectonic setting of formation in the Huanggangliang volcanic-extrusive uplift.It is composed of the rhyolitic crystalline tuff of the ash flow facies,the dome of the extrusive facies(rhyolite porphyroclastic lava),and porphyritic monzogranite of the superficial intrusive facies.Their SHRIMP zircon U-Pb ages are140.27 0.93Ma,140.41 0.92Ma and 141.75 respectively,which were produced by magmatic activities in the Early Cretaceous.The isotopic ages of the three lithofacies are consistent within the error range,indicating that there is no obvious discontinuity between the three lithofacies,and they are the products of continuous action of thick rich crystal magma(crystal mush).These volcanic-intrusive complexes belong to the high-K calc-alkaline series chemically,and are mainly peraluminous and quasi-aluminous rocks.The contents of Si O₂ and K₂O in magmatic products decreased continuously from early to late,and there is a certain complementary relationship between the compositions of different lithofacies,suggesting that rhyolitic crystalline tuff and rhyolite porphyroclastic lava may be discharged/emplaced layer by layer in the magma chamber of composition zonation,and the residual magma is filled into the ring fissure of volcanic root and surrounding to form porphyritic monzogranite-quartz monzonite.The volcano-intrusive complex is characterized by LILE enrichment(Rb,Th,U)and HFSE(Ti,Nb,Ta)strong depletion,and enriched LREE patterns with strong negative Eu anomaly.Geochemical characteristics indicate that they are A-type granite,and its genesis may be related to the upwelling of the asthenosphere mantle causing partial melting of the overlying lower crust under the extensional setting after the closure of Mongolia-Okhotsk Ocean in the Early Cretaceous.