Abstract

• The Khuntha-Mindaw area is situated in part of the 45-km long Monywa-Salingyi segment of Western Myanmar magmatic arc (WMA). Lithologically, the area comprises diorite, granite, gabbro, and pegmatite of intrusive and basalt, andesite, dacite and rhyolite of extrusive rocks which are formed during Cretaceous. These igneous rocks are overlain by Oligocene to Pliocene clastic sedimentary units with locally Upper Oligocene-Lower Miocene limestone. The mineral composition and textures of diverse rock units are analyzed and interpreted by binocular polarizing microscope and chemical composition by XRF from Department of Chemistry, Monywa University. Mineralogically, the volcanic rocks contain more than 20% phenocrysts of plagioclase feldspar, pyroxene, hornblende, biotite and quartz embedded in microlites to crystallites groundmass. The zoning, cumulophyric and resorbed textures indicate the fractional crystallization and magma mixing igneous activity in long-lived evolving magma. The multiple twinned plagioclase with interstitial quartz and orthoclase in granites suggest the calc-alkaline plutonic rocks. Petrochemically, the plutonic and volcanic rocks in the study area belong to the subalkaline series and falls within the calc-alkaline suite. Moreover, the major chemical compositions of the plutonic rocks fall within I-type and S-type granitoid field. Thus all igneous rocks exposed in the present area may be erupted from subduction related calc-alkaline magmatic volcanic-arc of convergent plate margins.