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Sarmistha Mukhopadhyay ¹, Jyotisankar Ray ¹, Basab Chattopadhyay ², Shyamal Sengupta ², Biswajit Ghosh ¹, Subrata Mukhopadhyay ¹

Affiliations
1 Department of Geology, University of Calcutta, 35, Ballygunge Circular Road, Kolkata - 700 019, IN
2 Geological Survey of India, Central Petrological Laboratories, 15 A&B Kyd Street, Kolkata - 700 016, IN

Abstract

The Elagiri complex (12°31' N: 78°35' E) represents one of the important silica - oversaturated syenite plutons of the Southern Granulite Terrane of the Indian shield. This article for the first time reports the mineral chemistry of the Elagiri complex and brings out important petrogenetic significance. The litho-members of Elagiri complex are intrusive into high grade country rocks viz. granite gneiss, amphibolite and pyroxene granulite. The country rocks are foliated bearing evidences of multiple folding and deformation. On the other hand, the constituent litho members of the Elagiri complex (syenites, gabbro and later intrusives marked by lamprophyre and carbonatite) show preservation of igneous layering in terms of discernible parallelism of the constituent minerals. The Elagiri complex shows presence of sharp contacts among litho members and marked absence of chilled facies peripheral to the margin. Electron microprobe data have been critically used to systematize the constituent mineral-phases of the different lithomembers of the complex. Geothermobarometric data indicate a temperature of equilibration in the range of ∼700° to 500° C at ∼2.0 to 5.2 kb which corresponds to shallow level (cf. 18.2 km) equilibration-depth of the complex. Field observations and mineral chemistry data suggest that liquid immiscibility plays an important role during the evolution of the Elagiri complex.

Keywords

Mineral Chemistry, Pyroxene Thermometry, Equilibration Depth, Liquid Immiscibility, Elagiri Complex, Indian Shield.

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Satabdi Das ¹, Nandini Dasgupta ¹, Sanjoy Sanyal ¹, Shyamal Sengupta ¹, Subrata Karmakar ¹, Pulak Sengupta ¹

Affiliations
1 Department of Geological Sciences, Jadavpur University, Kolkata-700 032, IN

Abstract

The Chotanagpur Granite Gneiss Complex (CGGC) of the East Indian Shield records a protracted geological history ranging from Palaeo- to Meso- to Neoproterozoic time. It is commonly believed that the whole of the CGGC behaved as a unified crustal block at least from 1600 Ma (ref. 3). The E-W to ENE-WSW trending North Purulia Shear Zone (NPSZ) dissects and geographically divides the CGGC into the northern and southern blocks.

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