Granitoids of the Khara Complex in the Eastern Bureya Continental Massif of the Central Asian Orogenic Belt: Age and Geodynamic Settings of Formation

Abstract

Petrogeochemical and geochronological studies were conducted on the main varieties of granitoids from the Sedelga and Berezovsky batholiths in the eastern Bureya continental Massif of the Central Asian Fold Belt. SHRIMP-II U–Pb zircon dating of granitoids constrained the time of formation to the Late Triassic and Early Jurassic between 208 to 193 Ma. Our studies revealed that the batholiths contain peraluminous granitoids of high K calc-alkaline series clearly enriched in Rb, K, Th, U, and Pb and relatively depleted in Nb, Ta, Y, HREE, Sr, Ba, Ti, and P and belong to I-type granites. Synthesis of the U–Pb geochronological data indicates that magmatism of tectonic blocks constituting the Bureya Massif at 213–183 Ma was accompanied by the emplacement of granitoid rocks of the Khara Complex. Strike-slip tectonics as a reflection of oblique collision of continental blocks and transform movement might have been an important mechanism of granitoid derivation in the Bureya Massif. Strike-slip faults were likely to penetrate deep into the crust initiating the ascent of an asthenospheric diapir and its fluids into the higher crustal levels thus transferring the heat and triggering melting with appreciable concentrations of Th, U, Rb, Pb and losses of Sr, P, Ba, and Ti. The depletion in Nb, Ta, Ti, and P and the enrichment in Pb make these granitoids similar to those of subduction zones. Granitoids of the Khara Complex display subduction-related (associated with the preceding subduction) and within-plate (associated with an asthenospheric diapir and its fluids) geochemical features, which is characteristic of transform margin environments. The most likely settings for granitoid magmatism to occur throughout the eastern margin of the Bureya Massif in the Late Triassic and Early Jurassic were transform settings associated with asthenospheric diapirism following the cessation of subduction.