Switching From Subduction Zone Advance to Retreat Explains the Late Paleozoic Evolution of the East Junggar System, Central Asian Orogenic Belt

Abstract

The geodynamic evolution of the East Junggar is examined by means of satellite imaging and field-based structural studies, U-Pb zircon geochronology and analysis of potential field geophysical data in the Yemaquan arc and the Dulate back-arc systems. The northern Yemaquan arc shows a pervasive WNW–ESE steep S₁ foliation that is related to the exhumation of Armantai ophiolitic mélange in an F₁ antiformal structure. The bedding of the Dulate sequences is folded by N–S-trending F₁ upright folds that are preserved in low strain domains. The timing of D₁ is estimated between 310 and 280 Ma. During D₂, previously folded Dulate sequences were orthogonally refolded by E–W-trending F₂ upright folds, resulting in Type-1 basin and dome interference pattern and pervasive E–W trending S₂ cleavage zones. The age of D₂ is constrained to be 270–250 Ma based on the dating of syn-tectonic pegmatites and deposition of syn-orogenic sedimentary rocks. The boundary between the Yemaquan arc and Dulate back-arc basin experienced reactivation through D₂ dextral transpressive shear zones. The D₁ fabrics are the consequence of the closure of the Dulate back-arc basin due to the advancing mode of Kalamaili subduction. Almost orthogonal Permian D₂ fabrics were generated by the N–S shortening of the East Junggar and the northward movement of the Junggar Block indenter. This D₂ deformation was associated with the anticlockwise rotation of the southern limb of the Mongolian Orocline, the scissor-like closure of the northerly Mongol-Okhotsk Ocean and the collision of the Mongolian and the Tarim–North China craton collages.