Heat Generation in Cratonic Mantle Roots—New Trace Element Constraints From Mantle Xenoliths and Implications for Cratonic Geotherms

Abstract

Modeled geothermal gradients, built from estimated thermal properties of the cratonic lithosphere, provide important insight into the thermal structure of Archean continental lithosphere. An important and yet poorly determined parameter affecting estimates of geothermal gradients within cratonic lithosphere, is the heat production in the cratonic lithospheric mantle (CLM) due to the decay of heat producing elements (HPE: K, U, and Th). Heat production in the CLM has been estimated by direct measurements of HPEs in mantle material (Goes et al., 2020;Rudnick et al., 1998;Russell et al., 2001) or by projecting geothermal models through pressure and temperature estimates from cratonic mantle xenoliths and varying heat production and other lithospheric properties to estimate the best-fits to the data (

Heat Transfer and Production in Cratonic Continental Crust: U‐Pb Thermochronology of Xenoliths From the Siberian Craton

“…Model C assumes an exponential decrease in crustal heat production. All models employ heat production value of 0.006 μW/m 3 for the mantle lithosphere (after McIntyre et al., 2021). Moho is at 45 km (after Cherepanova et al., 2013).…”

“…Model C assumes an exponential decrease in heat production, starting with the average tonalite heat-production at the surface and grading to an average mafic granulite value at 45 km depth for an integrated crustal heat production of 0.30 μW/m 3 . All of the models utilize a mantle lithosphere heat production value of 0.006 μW/m 3 (after McIntyre et al, 2021), a Moho depth of ∼45 km (Cherepanova et al, 2013), and are calculated with fixed surface heat flow values between 20 and 50 mW/m 2 (encompassing the range observed in cratons globally; Jaupart & Mareschal, 2014). Some interesting observations derive from these modeled geotherms.…”

Subaerial weathering drove stabilization of continents

“…Values of 2,800 and 3,300 kg m −3 were assumed for crustal and mantle density, respectively. Crustal heat production was varied between model runs but all calculations used 0.006 μW m −3 for heat production in the mantle lithosphere 83 . The upper surface of the model domain was held at 0 °C for all times and the base of the model domain was held at constant temperature, defined by the initial geotherm and assumed lithospheric thickness.…”

Evaluating the Rheological Controls on Topography Development During Craton Stabilization: Objective Approaches to Comparing Geodynamic Models

“… Metasomatism in CML — Set Met (3 models): at 0.00004 μW/m 3 , heat generation in unaltered sub‐continental lithospheric mantle is insignificant, but in localized regions affected by metasomatism, heat generation can increase to 0.18–0.27 μW/m 3 (McIntyre et al., 2021). Metasomatism is modeled by either elevating the heat production or weakening the rheology of a small region of the lithospheric mantle of the cratonic nucleus.…”

“…All other materials have a conductivity of 2.25 W m −1 K −1 . Heat generated through radioactive decay is restricted to the crustal layers in our models because un‐metasomatized depleted cratonic lithosphere is almost devoid of heat producing elements (McIntyre et al., 2021).…”