Abstract

• The Myitkyina mafic-ultramafic belt, eastern part of Kachin State, is a key to understand tectonic evolution of Tethys Ocean in SE Asia. We took a survey at the Washaung and Sadon villages about 9miles (14km) and 14miles (23km) respectively to east of Myitkyina Township where comprises magmatic rocks of pegmatite/aplite, hornblende granite, granodiorite, diorite, dolerite, peridotite and metamorphic rocks of amphibolite, hornblende-biotite gneiss, biotite gneiss and migmatite. Based on field criteria, petrographic data and previous published literature they jointly suggest that as the boundary between magmatic and metamorphic rocks is intrusive contact. The magmatic rocks have typical SSZ type (supra-subduction zone) features, suggesting products of partial melting of subduction oceanic plate. The subsequent partial melting of this underplated mafic rock may be caused by heat carried upward by basaltic magma. Fractional crystallization and contamination occurred when it passes through the crust. Some granite and pegmatite were probably formed by partial melting of lower or middle crust. The igneous are estimated to be Mid Jurassic to Cretaceous in age. All facts indicate the igneous rocks from the study area may be formed as continental arc which related to subduction of Neotethys Ocean during the Mesozoic and Early Cenozoic time.