Formation of the Back-Arc Slope of the Island Arc of Chingiz Caledonide Range in the Eastern Kazakhstan

Resumo

The formation of an island-arc back-arc slope is considered based on the of the Upper Cambrian‒Middle Ordovician arc in the Chingiz Range in eastern Kazakhstan. The study demonstrates its occurrence during waning volcanic activity in the island-arc structure, from the end of the early Arenig (end of the Floian Age of the Early Ordovician) with the appearance of tephroturbidites. After the cessation of volcanism, two sedimentation cycles were distinguished in the slope’s sedimentary sequence in the Middle Ordovician: (1) transgressive when the island arc submerged (2) and regressive when the Chingiz arc began to build up at the beginning of the Llanvirn (Darriwilian). Sedimentation was repeatedly accompanied by landslide processes, which ended in the middle of the Llanvirn (Darriwilian) with breakup of the tectonic-gravity plate composed of Upper Cambrian volcanic rocks with limestone in the sole, caused coarsely fragmented mixtite to form in front of the allochthonous mass and the further sedimentation on the back-arc slope to stop.