Radiogenic heat production of Late Archaean Bundelkhand granite and some Proterozoic gneisses and granitoids of Central India

Abstract

Abundances of heat-producing elements, K, U and Th, in some of the granites and gneisses of the Bundelkhand and Bastar terrains have been estimated by in situ gamma-ray spectrometry. The Bundelkhand granite is an I-type, calc-alkaline granite complex made up of porphyritic, coarse-to-medium grained and fine-grained granites. It carries macro enclaves of ~ 3.5 Ga-old tonalitic gneisses. These gneisses have a low heat production of 1.4 μWm^-3. The mean heat production of the dominant porphyritic and mediumto- coarse grained Bundelkhand granite is 5.5 μWm^-3. The heat production of the Proterozoic Jabalpur granite intruding the Mahakhosal greenstone belt is 3.4 μWm^-3. The Tirodi gneisses resulting from migmatization of psammopelites of the Sausar Group, are characterized by a mean heat production of 3.8 μWm^-3. The cataclastic biotite gneisses of the Tattapani geothermal area are the highest heat-producing rocks encountered in the Bundelkhand terrain with a mean heat production of 7.4 μWm^-3. The tonalitic Amgaon gneisses of the Bastar terrain are characterized by a heat production of 0.7 μWm^-3, which is about half of the mean heat production of the tonalitic gneisses occurring as inclusions in the Bundelkhand granite. Mean heat production of the Proterozoic Amgaon and Dongargarh granites are 2.5 and 2.9 μWm^-3, respectively. Preliminary heat production data presented here show that the gneisses and granitoids of the Bundelkhand and Bastar terrains may have distinct heat production ranges, with the rocks of the Bundelkhand terrain being more heat-producing.