Study on Cenozoic volcanic rock facies in the Cuomai area,Tibet

The Cuomai area of Tibet is situated in the middle part of the Gandise volcano-magma arc,in which there were strong volcanic activities in Cenozoic Ear and developed complete facies of volcanic rocks.The volcanic rocks can be divided into such seven main facies as explosive facies,explosion-efflusion facies,eruption-efflusion facies,extrusive facies,cryptovolcanic facies,volcanic vent facies,and eruption-sedimentary facies.Further,by its volcanic activities characteristics,the volcanic facies sequence,the facies assemblage features,and in combination with the volcanic-sedimentary strata and their contact relationship,the volcanic activity can also be classified into four eruption-sedimentation cycles in turn corresponding with such four stratigraphic units as Dianzhong Formation,Nianbo Formation,Pana Formation,Yulinshan Formation.The paper fully elaborates the basic characteristics of every type level of volcanic rock facies,preliminarily analyzes and concludes the facies sequences and facies assemblages of every type of volcanic rock,and cycles of volcanic activities,which is of actual significances in improving the study level of the volcanic rocks in the whole Gandis area.