Presentation Information
[R8-03]Reconstructing Neoproterozoic Radiogenic Heat Production in conjugate Gondwana Terranes of Sri Lanka and Southern India: Implications for Ultra-High-Temperature Metamorphism
*DEVIKA S PANICKER1 (1. Graduate School of Science and Technology, Niigata University, Japan)
Keywords:
Radiogenic heat production,Gamma-ray spectrometry,Neoproterozoic,Ultra-High-Temperature Metamorphism,Gondwana Terrane
Ultra-High-Temperature (UHT) metamorphism records peak temperatures exceeding 900 degree Celsius at 0.8-1.2 GPa, representing one of the most thermally extreme products of continental collision, yet its heat sources remain contentious. The Highland complex (HC) of Sri Lanka and the Kerala Khondalite Belt (KKB) of southern India preserve some of the most compelling evidence for UHT metamorphism at ~550 Ma, formed during the final stages of Gondwana assembly; however, the mechanism by which sufficient heat was generated and sustained in the deep crust has not been quantitatively evaluated. Here, we are testing whether the radiogenic self-heating of heat-producing elements (HPE) in the enriched thickened continental crust was thermally sufficient to drive to UHT conditions, without requiring anomalous mantle heat flux or other heat sources.
We present in situ U, Th, and K concentrations measured using portable gamma-ray spectrometry across the dominant lithologies of the HC and KKB. The dataset includes measurements from various rock types, such as charnockite, garnet-sillimanite gneisses, biotite gneisses, leptynite, mafic granulites, marble, migmatites, and pegmatites. Instrument calibration was validated using reference materials, and the calibrated HPE concentrations were used to calculate present-day radiogenic heat production (RHP), ranging from 0.02 to 32 microwatts per cubic meter in the HC, with the highest values recorded in felsic gneisses and charnockites. In the KKB, values range from 0.01 to 37.9 microwatts per cubic meter, with khondalites and garnet-biotite gneisses yielding the highest heat production. Furthermore, we reconstructed RHP at 550 Ma by applying isotopic decay corrections to measured present-day concentrations. Reconstructed RHP values are 1.5-2.5 times higher than present-day estimates, substantially elevating the thermal budget available during collision.
These reconstructed heat production values are integrated into one-dimensional thermal models of a doubly thickened (~70-80 km) collisional orogen to assess whether radiogenic self-heating alone or in combination with mantle heat flux can reproduce the P-T-t paths documented from UHT mineral assemblages. Our models demonstrate that HPE-enriched thickened crust, when corrected for Neoproterozoic age, generates geotherms capable of sustaining temperatures exceeding 900 degree Celsius at mid-to-lower crustal depths over geologically appropriate timescales (~20-40 Myr), without requiring tectonic or magmatic heat sources. This study provides the first direct, measurement-based quantitative test of the radiogenic self-heating hypothesis for UHT metamorphism in conjugate Gondwana terranes, moving beyond qualitative petrogenetic interpretations. Our findings have broader implications for understanding the role of HPE enrichment during crustal thickening in generating extreme metamorphism along the East African-Antarctic Orogen and for the thermal history of Neoproterozoic supercontinent assembly.
We present in situ U, Th, and K concentrations measured using portable gamma-ray spectrometry across the dominant lithologies of the HC and KKB. The dataset includes measurements from various rock types, such as charnockite, garnet-sillimanite gneisses, biotite gneisses, leptynite, mafic granulites, marble, migmatites, and pegmatites. Instrument calibration was validated using reference materials, and the calibrated HPE concentrations were used to calculate present-day radiogenic heat production (RHP), ranging from 0.02 to 32 microwatts per cubic meter in the HC, with the highest values recorded in felsic gneisses and charnockites. In the KKB, values range from 0.01 to 37.9 microwatts per cubic meter, with khondalites and garnet-biotite gneisses yielding the highest heat production. Furthermore, we reconstructed RHP at 550 Ma by applying isotopic decay corrections to measured present-day concentrations. Reconstructed RHP values are 1.5-2.5 times higher than present-day estimates, substantially elevating the thermal budget available during collision.
These reconstructed heat production values are integrated into one-dimensional thermal models of a doubly thickened (~70-80 km) collisional orogen to assess whether radiogenic self-heating alone or in combination with mantle heat flux can reproduce the P-T-t paths documented from UHT mineral assemblages. Our models demonstrate that HPE-enriched thickened crust, when corrected for Neoproterozoic age, generates geotherms capable of sustaining temperatures exceeding 900 degree Celsius at mid-to-lower crustal depths over geologically appropriate timescales (~20-40 Myr), without requiring tectonic or magmatic heat sources. This study provides the first direct, measurement-based quantitative test of the radiogenic self-heating hypothesis for UHT metamorphism in conjugate Gondwana terranes, moving beyond qualitative petrogenetic interpretations. Our findings have broader implications for understanding the role of HPE enrichment during crustal thickening in generating extreme metamorphism along the East African-Antarctic Orogen and for the thermal history of Neoproterozoic supercontinent assembly.