Petrogenesis of Volcanic Rocks from Dhanjori Basin, Singhbhum Craton

Thakur, Abhinav (2021) Petrogenesis of Volcanic Rocks from Dhanjori Basin, Singhbhum Craton. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS Dissertation of Abhinav Thakur (15MS072)) 15MS072_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (5MB)

Abstract

On the basis of their petrography and geochemistry, volcanic rocks in the type section of Dhanjori basin in the Precambrian Singhbhum Protocontinent can be divided into primitive and evolved members. The primitive member includes massive and at certain places, pillowed volcanic units, mainly basalt and basaltic-andesite with intrusive and extrusive rocks of similar major and trace element composition. Rocks of the evolved member are in general massive and fine grained with an alteration mineral assemblage similar to that of the primitive ones, except for higher proportions of actinolite-tremolite, chlorite, serpentine, and opaque minerals, but scarce feldspar. Most of the rocks consist of a typical greenschist-facies mineral assemblage, consisting of actinolite, tremolite, chlorite, and quartz and subordinate pyroxene. A few volcanic units of the Upper Dhanjori formation, with its close proximity to the Singhbhum shear zone are weakly metamorphosed to Amphibolites facies. Large variations in the amount of Cr and Ni content relative to the major elements of the coarse-grained primitive are consistent with partial accumulation of olivine. The interlayering of the primitive and evolved volcanic rocks throughout the spatial extent of the type section of Dhanjori basin suggests a genetic relationship between the two groups.

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