Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

Subhasish Ghosh ¹, S. Chakraborty ², J. K. Bhalla ³, D. K. Paul ¹, Amitabha Sarkari ¹, P.K. Bishui ¹, S. N. Gupta ¹

Affiliations
1 Geochronology and Isotope Geology Division, Geological Survey of India, Calcutta-700 016, IN
2 Petrology Division, Geological Survey of India, North Eastern Region, Shillong, IN
3 Geochronology and Isotope Geology Division, Geological Survey of India, Calcutta - 700 016, IN

Abstract

Discordant granite plutons at Kyrdem, Nongpoh and South Khasi intrude the basement gneisses and the overlying Shillong Group of metasediments in the Meghalaya Plateau. Porphyritic granitoids ranging in composition from quartz monzonite to granite represent the dominant component in all the three plutons. Common characteristics of these granitoids arc spatial association with hornblende dioritic rocks, dominantly potassic and metaluminous nature. A positive correlation of SiO₂, Na₂O + K₂O, Rb, Rb/Sr and negative correlation of CaO, MgO, FcO(T), Sr, TiO₂ with Differentiation Index in the Kyrdcm pluton point to fractional crystallisation processes. Rb-Sr whole rock isochron data of the plutons yield ages in the range 480-690 Ma wiLh initia1 ⁸⁷Sr/⁸⁶Sr ratios ranging from 0.70948 -0.71482. Absence of post emplacement tcctonolhennal event is suggested by near concordant K-Ar biotite ages.

A protracted thennal event during late Proterozoic-early Palaeozoic (500-700 Ma), possibly related to mantle upwelling, possibly triggered the generation of these granitoids.

Keywords

Geochrmology, Geochemistry, Granitoids, Khasi Hills, Meghalaya.

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S. Chakraborty ¹, P. K. Paul ¹

Affiliations
1 Department of Mining & Geology, Bengal Engineering College (D U), Howrah - 711 103, IN

Abstract

Remote sensing techniques using satellite imagery have proved to be an indispensable tool in morphometric analysis and groundwater studies. Remote sensing techniques with an emphasis on lineament identification plays a great role in groundwater prospecting and applied on hard rock areas of Purulia district. In this work Morphometric and Hydrogeomorphic analysis has been done to determine the potential water-bearing zone in the study area. Groundwater occurs at shallow depth under water table condition within the weathered mantle, fractured hard rock and the narrow zone of unconsolidated sediments, along major river valleys. High fluctuation of water table is observed mostly from valley fills to weathered pediments.

Keywords

Groundwater, Remote Sensing, GIS, West Bengal.

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