Abstract

• The Cenozoic Mogok metamorphic belt exposed at the western margin of the Shan-Thai Block consists of metaigneous and metasedimentary rocks with various granitoid intrusions. The common mineral assemblages of gneiss samples are characterized by garnet + biotite + plagioclase + Kfeldspar + quartz with cordierite and sillimanite in some samples forming under upper amphibolite to granulite facies conditions. Geochemical data were used to evaluate the possible protolith composition, sourece–area weathering, provenance and tectonic setting of the gneiss samples. Sagaing samples are more enriched in Fe relative to Onzon and Thabeikkyin samples. Compared with average crustal content the samples show similar composition with depletion of CaO, Na2O, P2O5, Sr and Nb and enrichment of Rb, Y and Th. Evidences form major and trace element concentrations, ratios and use of various diagrams point to the derivation of Onzon and SM2 unit samples from psammitic composition mainly greywacke and SM1 unit sample from pelitic compositions except for Thabeikkyin sample, which has felsic igneous protolith. In addition, Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), Index of compositional Variability (ICV) values and major element diagrams indicate that the source areas had undergone moderate to high degree of weathering. Based on the major and trace variation sediment deposition might have occurred at passive margin and active continental margin.