Methane-bearing fluid inclusions as evidence of the collisional nature of high-alumina granites, northern Sikhote-Alin, Russian Far East

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