ALBERT

Description: Knowledge of the downward variation of thermal conductivity within Earth's interior is an essential parameter for accurately estimating the sub-surface temperature distribution. The variation is dominantly controlled by temperature and, to a very less extent, by pressure. The temperature dependence is distinct for various rocks and higher for upper crustal rocks than the lower crustal rocks, implying the utmost necessity of detailed study for upper crustal rocks. In thermal modeling, two temperature coefficients are commonly considered for the upper and lower crust. But the upper crust generally consists of a wide variety of rocks. In the present study, thermal conductivity variation with temperature has been studied in the laboratory by a steady-state method in the temperature range of 25-300 °C on different types of upper crustal rocks, e.g., granitoids and rhyolites. Results show that the temperature dependence of thermal conductivity for different varieties of granitoids, i.e., alkali feldspar granite to monzogranite and granodiorite to tonalite to quartz diorite, indicate two distinct ranges and rhyolites lie between these two varieties. The study also depicts that a single temperature coefficient for the upper crustal rocks needs to be modified, and appropriate values should be considered, depending upon the variations in rock formation of the upper crust. The observed wide variations in the temperature dependence of thermal conductivity for different varieties of upper crustal rocks will be useful for precise sub-surface thermal modeling. The study also investigated how the difference in temperature coefficient for the upper crust can produce a difference in thermal structure.

Description: The Godavari is one of the largest Gondwana basins in India and developed by the extensional tectonic activity of the intra-cratonic continental rift of Paleoproterozoic age. It is situated between the Dharwar and Bastar cratons. In the present study, temperature measurements were carried out in the southeastern part of the basin from two deep boreholes (up to 1000 m) and the maximum temperature observed is 81 oC. Thermal conductivity of 60 core samples representative of major lithologies penetrated by the boreholes was measured under steady-state conditions. The average thermal conductivity is lowest for shale and siltstone, intermediate for sandstone, and highest for quartzite. The estimated heat flow values range between 70 and 95 mWm-2. Considering the previous studies, heat flow in the southeastern and southern part of the basin (64-104 mWm-2 with a mean of 86 mWm-2, N=5) is comparatively higher than western part (52-84 mWm-2 with a mean of 63 mWm-2, N=5). Geophysical studies (magneto-telluric and gravity) along with the thermal data indicate that the high heat flow in the southeastern and southern parts of the basin could be due to the existence of geothermal reservoir in the basement and water circulations in the sedimentary formations along the fault/fracture systems. Hot springs with a maximum water temperature of ~81 o C in the region also supports the observed high heat flow. The present data will be used to construct a subsurface thermal model of the basin which will further be utilized in assessing the geothermal reservoir of the region.

Description: Thermal modeling of the lithosphere is essential to understand the geodynamics, seismogenesis, and crustal evolution of any region. Surface heat flow, radiogenic heat production, and thermal conductivity variations with temperature are the primary parameters that influence thermal modeling. The Western Himalaya is devoid of all these parameters, which hindered accurate thermal modeling of the region. In the present study, we have measured the above thermophysical properties in the laboratory for the major rock formations of the Western Himalaya along three NW-SE profiles. The major rock formations include sandstone, limestone, dolomitic limestone, slate, phyllite, quartzite, schist, gneiss, and granitoid. Thermal conductivity and heat production of these rocks vary from 2.6 to 5.4 Wm〈sup〉-1〈/sup〉K〈sup〉-1〈/sup〉 and 1.7 to 2.6 µWm〈sup〉-3〈/sup〉. The crustal structure along one of the profiles, i.e., Tanakpur-Pangla profile (150 km length), is made using available geological and geophysical (seismological and gravity) information, along with new data on rock thermal conductivity and its variation with temperature and radiogenic heat production to obtain 2D conductive thermal structure beneath the region by finite element method. The 2D temperature-depth distribution along this profile covering Siwalik, Lesser Himalaya, and Higher Himalaya formations reveals that the temperature at Moho varies from 450 °C to 750 °C. At a few locations, subsurface temperatures estimated from the 1D conductivity models are in good agreement with that of the 2D results within the uncertainty limits. The results of 2D thermal modeling provide significant progress in understanding of the first-order characteristics of the conductive thermal field in the Western Himalaya.

Description: Heat flow plays a vital role in estimating the lithospheric temperature distribution, which is an essential parameter in understanding the evolution and stabilization of the cratons. Heat flow is determined in the Mesoarchean Singhbhum Craton, one of the oldest cratons in the Indian shield, for the first time from seven locations. This enabled us to construct plausible 1-D crustal thermal models and to estimate mantle heat flow by considering a few crustal heat production/thermal conductivity models based on crustal structures from the geological/geophysical studies of the study region. In the present study, detailed radioelemental abundances (Th, U, K) and heat production are measured for the Paleoarchaean gneiss (OMTG) and Singhbhum Granites (SBG) of the craton. The result shows that both OMTG and SBG, which cover most of the craton, have, in general, low radioelemental abundances and heat production with an average of 1.3 ± 0.2 mWm〈sup〉-3〈/sup〉. Heat flow ranges from 27-34 mWm〈sup〉-2〈/sup〉, with an average of 30 ± 3 mWm〈sup〉-2〈/sup〉, which is lowest than most of the cratons. Interestingly, the value is also half that observed in the Singhbhum Shear Zone (61 ± 2 mWm〈sup〉-2〈/sup〉), situated in its north. The 1-D thermal models indicate that mantle heat flow and Moho temperature range from 14-16 mWm〈sup〉-2〈/sup〉 and 330-370 °C, respectively. These fall within the range observed for the Archaean cratons despite their lowest surface heat flow. It is mainly due to the distinct crustal heat production scenarios and upper crustal thermal conductivity profiles, which provide clues to understanding the craton formation.

Description: The data publication contains the compilation of global heat-flow data by the International Heat Flow Commission (IHFC; www.ihfc-iugg.org) of the International Association of Seismology and Physics of the Earth's Interior (IASPEI). The presented data update release 2024 contains data generated between 1939 and 2024 and constitutes the second intermediate update benefiting from the global collaborative assessment and quality control of the Global Heat Flow Database running since May 2021 (http://assessment.ihfc-iugg.org). The data release comprises new original heat-flow data published since April 2023 (the update 2023). It contains 91,182 heat-flow data from 1,586 publications. 57% of the reported heat-flow values are from the continental domain (n ~ 54,553), while the remaining 43% are located in the oceanic domain (n ~ 36,692).