Syntectonic metamorphism of a collisional zone in the Tuva-Mongolian massif, Central Asian Orogenic belt: P-T conditions, U-Pb ages and tectonic setting

Abstract

Accretionary-collisional events occurred at the western margin of the Tuva-Mongolian microcontinent are used to explain the largely contradictory Cambrian geodynamic history of the western Central Asian Orogenic Belt (CAOB). This study presents new data for the Erzin metamorphic complex in order to constrain the petrogenesis and tectonic implications of the metamorphic rocks in this complex. The Erzin complex in the tectonic Erzin zone is composed of high-grade metamorphic rocks that have formed under variable metamorphic conditions (T = 730–835 °C, P = 5.3–7.5 kbar). In the Erzin complex, metamorphic rocks have undergone multiple stages of ductile deformation with subvertical mineral lineation and were then superimposed by sub-horizontal ductile deformation. The stages of tectonic deformation are close in time and mark collisional stages characterized by a sequential change from the compression regime to the extension regime in the period of 495 ± 5 Ma. The determination of the time interval is based on structural and petrological data, previously published materials, as well as the dating of granite dikes (U-Pb, zircon) sealing the Erzin complex. P-T conditions and structural-petrological studies analysed in this paper suggest that the formation of the Erzin metamorphic complex occurred as a result of a collisional event between the Tannuola island arc and Tuva-Mongolian microcontinent. We suggest that the Erzin metamorphic complex is important for study of transitional regime between the collisional event and initial orogenic collapse in the ancient fold belts. Metamorphic record of the Tuva-Mongolian microcontinent provides important information about the processes that occurred at the Early Paleozoic geodynamic evolution in the western CAOB.