Studies on Quaternary volcanism stages of Nuomin river area in the Great Xing'an Range:Evidence from petrology,K-Ar dating and volcanic geology features

24 Quaternary volcanoes are distributed along Nuomin river and Kuile river area volcanic field(NK for short) in the north of the Great Xing'an Range,With an area of 600 square kilometers,the volcanic rocks are characterized by potassic series(K2O=2%～4%,K2ONa2O-2%),which are similar with rocks in Wudalianchi-Keluo volcanic field(WK for short),Although NK and WK share the alike mantle source,volcanic rocks from NK are low in K2O than that from WK(K2O=4%～6%),During the Paleozoic and the Cenozoic,multiple tectonic and magmatic activities resulted in the heterogenous geochemistry in the magma source,and thus varied volcanic rocks were generated,Based on K-Ar dating(2.3～0.128Ma) and volcanic field characteristics,it is identified that the volcanism in NK occurred in four periods:Early Pleistocene,Middle Pleistocene,Late Pleistocene,and Holocene,Volcanic products of Early Pleistocene,mostly mantled by the later volcanic rocks,are distributed along the valleys of Nuomin river and Kuile river,Middle Pleistocene volcanism formed most of the volcanoes and lava spreading in NK,In Late Pleistocene and Holocene Period,volcanic activities were confined in Bila river area,and well kept Sifangshan volcano and Maanshan volcano exemplify volcanism in this period,According to the distribution of volcanoes in four periods,it is inferred that the volcanism have the tendency to develop from the east to the west of NK.