CARBONIFEROUS VOLCANISM IN NURT AREA OF ALTAY, XINJIANG

Nurt area is located in the north of the Altay area, at the southwest of the Siberia plate. Carboniferous volcanic rocks are scattered along the Hongshanzui fault system and mainly occur in Lower Carboniferous Hongshanzui Formation. Lithology of Carboniferous volcanic rocks include crystal fragment tuff, cataclasite lava, tuff, volcanic breccia and rhyolite. Carboniferous volcanic rocks formed at the interim from convergent stage to new continental crust stage of the crustal evolution, and the eruptive environment was land environment, the volcanic rocks belong to the acidic, high kalium and calcium-alkalescence series. The forms of eruption include explosion, effusion and extrusion, and volcanic rocks have explosion-effusion faces, fall out faces, extrusion faces and eruption-sedimentary faces. Studies on the petrology and the volcanic rock facies and the contrasts of the columnar sections of Carboniferous volcanic rocks show that, in the Nurt area, Carboniferous volcanic activities controlled by the fault system had the type of fissure-central eruption, the centres of volcanic activities were located in Tuogertuobie and Kuokeyidalasi and the forms of eruption mainly were explosion-effusion, however, Tasibige, Aktiskan and Kumasu were far away from the centres and the forms of eruption mainly were extrusion, moreover, the intensity of volcanic activities wore off from west to east.