Abstract

The Himalaya, Kohistan, and Karakoram ranges comprise Proterozoic to Cenozoic crystalline complexes exposed in northern Pakistan. Numerous hot springs in the area indicate high subsurface temperatures, prompting a need to evaluate the local contribution of radiogenic heat to the general orogenic-related elevated geothermal gradients. The current study employed a portable gamma spectrometer to estimate the in-situ radiogenic heat production in the Nanga Parbat Massif, Kohistan–Ladakh batholith, and the Karakoram batholith. Heat production in the Nanga Parbat Massif is high, with a range from 0.2 to 10.8 µWm−3 and mean values of 4.6 ± 2.5 and 5.9 ± 1.9 µWm−3 for gneisses and granites, respectively. By contrast, the heat production is low in the Kohistan–Ladakh batholith, ranging from 0.1 to 3.1 µWm−3, with the highest mean of 2.0 ± 0.5 µWm−3 in granites. The Karakoram batholith shows a large variation in heat production, with values ranging from 0.4 to 20.3 µWm−3 and the highest mean of 8.4 ± 8.3 µWm−3 in granites. The in-situ radiogenic heat production values vary in different ranges and represent considerably higher values than those previously used for the thermal modeling of Himalaya. A conductive 1D thermal model suggests 93–108 °C hotter geotherms, respectively, at 10 and 20 km depths due to the thick heat-producing layer in the upper crust, resulting in a surface heat flow of 103 mWm−2. The present study provides first-order radiogenic heat production constraints for developing a thermal model for geothermal assessment.

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