Permian volcanism in the Sawu'er area,western Junggar

The Sawu'er area in western Junggar is located in Jeminay County of the Altay region and Hefeng County of the Tacheng region,Xinjiang.Volcanism occurred in the area during the Middle Devonian to Early Permian,and it was particularly strong in the Permian.Permian volcanic rocks include the Ha'erjiawu Formation and Kalagang Formation.The Ha'erjiawu Formation consists of a suite of intermediate-basic and intermediate continental volcanic rocks and pyroclastic rocks,and the Kalagang Formation consists of a suite of intermediate-basic and intermediate-acid volcanic rocks and pyroclastic rocks.The volcanic rocks of the Ha'erjiawu-Kalagang cycle include olivine basalt,basalt,trachybasalt,andesite,trachyandesite,rhyolite and pyroclastic rocks.According to the composite stratigraphic section of volcanic rocks and lithological and petrographic characteristics of volcanic rocks,the Permian volcanism in the Sawu'er area occurred in five phases;they are from early to late as follows:the intermediate volcanic eruption phase,intermittent basic volcanic eruption phase,acid volcanic eruption phase,small-scale intermittent intermediate volcanic exploration phase and basic volcanic outpouring phase.The Permian volcanic rocks are continental ones and have the characteristics of typical bimodal volcanic rocks.They formed in an extensional setting.