Alkaline intrusion in a granulite ensemble in the eastern ghats belt, India: Shear zone pathway and a pull-apart structure

Abstract

The alkaline complex of Koraput, Orissa, India, is one of several bodies in the high-grade Eastern Ghats belt, but this one is an integral part of the high-grade belt and remote from the western boundary against the Bastar craton. The Koraput complex forms a lozenge-shaped intrusion into the metapelitic granulites and is bounded by shear zones. The combined effect of movement along these shear zones, is a northeasterly elongated sygmoidal cavity with maximum width along the northwesterly trending Reidel shear. Thus the Koraput alkaline complex can be considered to have been emplaced in a pull-apart structure, developed in the granulitic country rocks. Moreover, in view of the fact that the western margin of the high-grade Eastern Ghats belt bears clear evidence of collisional features, rather than that of rifting or break-up, the rift-valley model for the alkaline magmatism in this high-grade belt appears untenable.

Contrasting magmatic signatures in the Rairakhol and Koraput alkaline complexes, Eastern Ghats belt, India

“…This body shows distinct intrusive contact, dominated by magmatic fabrics, no tectonic folds and only occasionally thin shear bands that are interpreted as syntectonic fabric with that in the metapelitic country rocks (Bhattacharya and Kar 2004). Sodic amphibole, acmitic clinopyroxene, annite-rich biotite and sodic plagioclase are typical minerals of an alkaline complex.…”

Electron Microscopic Studies of Ilmenite from the Chhatrapur Coast, Odisha, India, and Their Implications in Processing

“…Hence, the Eastern Ghat group of rocks appears to be the major source for the ilmenite. Outcrops of igneous intrusive rocks in the Eastern Ghat group also suggest that the ilmenites were formed in a high grade metamorphic environment [25]. The wide ranges of the V 2 O 5 (0.247% to 0.306%), Cr 2 O 3 (0 to 0.089%), and NiO (0 to 0.051) content indicates that the ilmenites from this area represent an admixture of multiple of source rock types.…”

Eastern Ghats Mobile Belt

“…This was followed by high-pressure isobaric cooling (IBC) as documented by the reaction coronas formed from the reactions involving Spr+Spl+Qz (formed at the thermal peak) . There is, however, a serious controversy in respect of the retrograde P-T trajectory, which according to Lal (1997), Bhattacharya and Kar (2004), is clock-wise, whereas Dasgupta et al (1997) and Sengupta et al (1990) deduced anticlockwise paths for the investigated localities of the NEGMB. The P-T trajectories by different authors (see Fig.…”