ANALYSIS ON GEOCHEMICAL CHARACTERISTICS OF VOLCANIC ROCKS OF SUXIONG FORMATION IN MIANNING AREA,SICHUAN

摘要

In order to analyze the petrological and geochemical characteristics of the Suxiong Formation volcanic rocks in the Mianning area of the Sichuan Basin in southwestern China,clarify the formation age of the Suxiong Formation volcanic rocks,analyze the magma origin of the volcanic rocks in this area,and the tectonic environment of the formation of the volcanic rocks,the LA- The ICP-MS zircon U-Pb isotope method is used to date samples of the Suxiong Formation volcanic rocks in this study.The ages of the two samples are 821.6±4.3Ma and 835.5±3.9Ma,respectively.The diagenetic age of the volcanic rocks is determined to be Late Qing Bai-kou Period-Early South China Period.The geochemical study of the volcanic rocks of the Suxiong Formation shows that the volcanic rocks belong to the high-potassium calcium-alkaline series.The main elements are rich in K2O,rich in AI2O3,low in MgO and Ti02.The light rare earth is relatively enriched,and Eu is negative anomaly,which is the result of the separation and crystallization of plagioclase.The trace elements are relatively enriched in Rb,Th,K,La,Ce,Nd,Zr,Hf,Sm,Y,Yb and Lu,and relatively deficient in Ba,Ta,Nb,Sr and Ti.Compared with La-Th,Nb-Ta is obviously depleted,and it has the characteristic of volcanic rock with typical volcanic arc.The loss of Ba,Sr,and Ti indicates that the Suxiong Formation volcanic rocks are most likely derived from partial melting of the crust.Finally,combined with the geological environment,rock assemblage and tectonic environment of the volcanic rocks of the Suxiong Formation,it is believed that the volcanic rocks of the Suxiong Formation were formed in the volcanic arc structural environment of the continental margin.