Geochemistry of Jianquanzi Volcanic Rocks in Beishan Area,Gansu Province

The Jianquanzi area of Beishan in Gansu Province is designated as Silurian Gongpoquan Group originally.Lithology combination includes quartz greywacke,conglomeratic gritstone interbedded thin-layer limestone,siltstone with Bouma sequenced,and volcanic rock.Chemical analysis data of volcanic rock show that the major elements and microelements are very different from island-arc volcanic rocks,it indicates that they are not derived from the island-arc environment.Crystalline limestone produces the corals fossil(designated as the Silurian Altaja).This study collects data and redefines the volcanic rock as Dohophyllum reticulatum Fomitchev,? Paracarruthersella sp.and foraminifer,and age is Late Carboniferous.The age of fossil and geochemical characteristics of volcanic rock reveal that there is no island arc volcanic rocks exposed on the south side of the Hongliuhe-Niujuanzi-Xichangjing ophiolite belt in the entire Beishan region.In conclusion,there is no volcanic evidence of the southward subduction in the Paleozoic tectonic evolution in the study region,which has an important foundation of improving the framework of Beishan Paleozoic tectonic evolution.