The Research Of Geochemistry And Geochronology Of The Samalongwa Granodiorite Porphyry Of The Litang Area In Sichuan Province

The Litang area in Sichuan province is located in the middle of the ‘Three-River' orogenic belt in China,which is in the joint terrain of the Eurasia plate and India plate,located in the eastern extension of the Eastern Tethys,an important polymetallic metallogenic belt of China.Yidun-Shaluli arc is dominated by Cuojiaoma,Dongcuo huge batholith,that macroscopic inverted "S" type granite belt,which has experienced a multi-stage complex plate tectonic evolution.It has a good mineralization geological environment,forming a very rich mineral resources,and granite-related minerals are lead,zinc,tin,silver,gold and rare elements.This study researches on petrography,petro-geochemistry and chronology of the Samalongwa granodiorite porphyry,it discusses the granite origin,the tectonic setting and its geological significance.The Samalongwa rock mass in the study area is mainly incanus massive granodiorite porphyry,which is intruded into the Tumugou Formation.The content of SiO2 of all six samples is between 61.59%-63.38%,to belong to middle-acid rock category,quasi-aluminum,high potassium calcium alkaline-potassium rock.To exclude late alteration of rocks,the Samalongwa granodiorite porphyry is quasialuminum,high-potassium,high-sodium,and low-titanium.The rare earth content of the six samples of the granodiorite porphyry is high,?REE=152.61×10-6-167.53×10-6,average value is 157.75×10-6.The rare earth elements have similar characteristics,with inclining to the right and riching in LREE and lack of HREE.The curves of the six samples of the granodiorite porphyry on the PM normalized spidergrams,while the granodiorite porphyry are significantly depleted in high field strength elements(HFSE)Nb,Ta,Ti and P as well as the large ion lithophile elements(LILE)Rb,Th,K enrichment,indicates that it's magmatic origin is related to plate subduction.The age of the zircon U-Pb granodiorite porphyry obtained in the study area is 220.1±1.4Ma,and the formation time should be in the Norian of Late Triassic.Combined with previous studies,the Ganzi-Litang ocean had been developed in the early Carboniferous,and became largest ocean in the Permian-Early Triassic.The Ganzi-Litang ocean basin mostly happened westward subduction as early as Middle Triassic,leads to the mantle wedge partially melting,and large numbers of basaltic magma transferred to the lower-crust.The ocean basin subduction sustainable to late Triassic and reaches its peak,leads the early stage basaltic lower-crust partial melting,which formed the original magma of the granodiorite porphyry.The majority of magma with diapirism which roses to the recent surface formed the Samalongwa rock mass.The Late Triassic granitic magmatic rocks provide the source of the formation of abnormal elements in the study area.The elemental anomalies in the study area are mainly related to the hydrothermal activity of the middle-acid magma.The angle rock zone between the medium-acid rock mass and the surrounding rock is a favorable part of the prospecting.