Thermal contribution of radiogenic heat in volcanic rocks of the Martin Vaz archipelago, South Atlantic Ocean

The thermal structure of the lithosphere reflects the balance between mantle heat input and radiogenic heat production within the crust. Quantifying heat-producing elements (U, Th, and K) is therefore critical for understanding the thermal evolution of oceanic volcanic systems. This study presents the first integrated assessment of surface radiogenic heat production (SRHP) and flux (SRHF) for the Martín Vaz Archipelago, the terminal eastern volcanic expression of the Vitória–Trindade Ridge in the South Atlantic Ocean. Uranium, thorium, and potassium concentrations were determined using whole-rock geochemistry together with laboratory and in situ gamma-ray spectrometry, enabling high-resolution quantification and spatial mapping of radiogenic heat sources. The results reveal significant variability in the concentrations of these elements. Th/U ratios are highly dispersed, with an average value of 7.4, considerably higher than the continental crust average of 3.9, suggesting geochemical decoupling between uranium and thorium. Calculated SRHP values range from 1.79 to 4.17 μW m -3 (average of 2.7 μW m -3 ). Estimated SRHF values range from 87 to 90 mW m -2 , exceeding both the global mean heat flux (60 mW m -2 ) and the Brazilian continental average (59 mW m -2 ). Although evolved phonolitic units locally increase radiogenic heat production, crustal radioactivity alone cannot explain the elevated heat flux. These results indicate a thermal regime predominantly controlled by mantle-derived heat input, consistent with the intraplate oceanic setting and models involving mantle plume activity and lithospheric fracturing.