The Sequence of Deformation, Metamorphism and Igneous Intrusion in the Area around Angul (Orissa)

The area around Angul (20°50'N, and 85°05'E) at the north-eastern part of the Eastern Ghats belt, is characterised by highly metamorphosed Archaean catazonal meta-sediments which were syntectonically intruded by a group of hitherto unreported igneous rocks, viz. anorthosite, norite, gabbro and acid charnockite suite sensu stricta. The acid charnockites are generally conformable to the country rocks but clearly show intrusive features in several localities. Along with the surrounding country rocks the syntectonic igneous rocks are highly deformed and metamorphosed under hornblende-granulite subfacies condition. A homophanous biotite-granite, pegmatite-vein quartz and dolerites are post-tectonic discordant intrusions. The paper discusses the geological succession of the area with special reference to the relation between deformation, intrusion and metamorphism of the meta-sediments and the igneous rocks. Among the intrusives, anorthosites are early tectonic and charnockites are late tectonic in nature. Emplacement of norites took place during the main phase of deformation and even slightly outlasted the major folding movement. The maximum regional metamorphism took place in the late tectonic period after the emplacement of charnockites and was followed by granitisation of the rocks to some extent. The post-tectonic intrusions do not show any regional metamorphic effect; but the dolerite shows evidence of auto-metamorphism.