A Geochemistry Study Of The Suxiong Volcanic Rocksin Mianning Area,Sichuan Province

The Suxiongvocanic rocksfoundin Mianning areais apart of thenorthern Kangdian axis located in the west of the Yangtze block. With the using of petrology, geochemistry analysisand zircon U-Pb determination, we haveidentified thepetrology, geochemical characteristic-cs and clarified the emplacement age of the Suxiong vocanic rocks in Mianning area.Moreover, the origin and evolution of the Suxiongvolcanic rocks has been discussed to further studythe tectonic environment.Petrology study results show that the Suxiong volcanic rocks are mainly consisted ofvolcanics pyroclastic rocks, acidic volcanic lava, with less amount of basic lavasvolcanic-clastic sedimentary. The petrology facies are composed ofoverflow phase, sedimentary facies and the dominent erupted facies. The age fromtwo samples heredetermined by LA-ICP-MS zircon U-Pb isotopes analysis are 821.4 ± 4.3Ma and 835.6 ± 3.9Ma respectively suggest that the Suxiong vocanic rocks were eruptedbetween late Qingbaikou and early Nanhua period.The geochemical study show that the Suxiong volcanic rocks plot in the high-K alkaline rock series.The major elements enrich inK2O(2.59%-6.17%) and Al2O3(11.62%-14.93%), with relative lower content of MgO(0.58% ~ 0.1%) and TiO2(0.09% ~ 0.50%). The content of SiO2 and CaOin Harker diagram given in this paperpresent a large variability,which is possibly caused by carbonatization or weathering. On the other hand, the rare earth elements resultsfrom the Suxiong volcanic samplesgiven here display high content of total earth elements rangingfrom 170.59 to 400.85. Notablely, the light and heavy rare earth elements fractionate apparently with light rare earth enriched and anomalies depletion of Eu resulting from the crystallization plagioclase from former magmas. The enrichment of trace elementssuch as Rb, Th, U, K, La, Ce, Nd, Zr, Hf, Sm, Y, Yb and Lu and relatively depletion of Ba, Ta, Nb, Sr and Ti. Nb-Ta relative to La-Th share typical features of volcanic arc in the volcanic samples.The depletion of Ba, Sr and Ti elements indicated that the Suxiong volcanic rocks most likely origined from the partial melting of the crust. Integrated geological environment, petrology associations, specific tectonic discrimination of the Suxiong volcanic rocks in Mianning area supported that Suxiong volcanic rockswere formed in a continental margin volcanic arc setting in study area.