Methane-Bearing Fluid Inclusions as Evidence of the Collisional Nature of High-Alumina Granites, Northern Sikhote-Alin, Russian Far East

Abstract

The Khungariisk high-alumina S-type granites (northern Sikhote-Alin fold system, Russian Far East) have been formed as a result of anatectic melting during collision of the Anyuy sialic block with the continental margin in the Early Cretaceous. Methane-rich fluid inclusions are characteristic of these granites. The CH4-H2O fluid composition is explained by the release of water and methane from the sedimentary units residing on the oceanic plate, as it was subducted beneath the sialic block. This fluid seeped into the heated and deformed metamorphic rocks of the overlying block and initiated partial fusion of the granites. A comparison of the new data with the results of fluid-inclusion studies of high-alumina collisional granites from the Pamir Mountains and Japan reveals similarities. Thus, methane-bearing fluid is probably one of the general features of this granite type, reflecting its anatectic origin.