GEO Solid Brown Bag Seminar

Mar 30, 2023, 12:30 pm1:20 pm
Guyot 220



Event Description

The decay of radioactive elements—like U, Th and K—produces heat and the dissipation of this heat from Earth's interior drives mantle convection and plate tectonics. Significant portions of Earth’s heating-producing elements (HPEs) are proposed to be sequestered within the continental crust, yet the HPE budget of the crust is uncertain, with current estimates varying between 25–95% of the bulk silicate Earth. In stable continents, surface heat flux represents the total amount of heat exiting the lithosphere and reflects inputs from HPEs within the crust and heat entering the base of the crust from the underlying mantle. Temperatures of the lower crust are thus key in unraveling the contributions of the mantle and crust to the total heat budget of the lithosphere. Here I will present a case study of crustal heat production in the Siberian craton (Russia) that uses xenoliths—fragments of the deep crust transported rapidly to the surface by volcanism—to reconstruct the temperature-time history of the lower crust and constrain long-term residence temperatures. High-spatial resolution U-Pb thermochronology and multi-element diffusion chronology in accessory minerals from deep crustal xenoliths reveal a relatively cool lower crust (<400  °C) that experienced multiple transient heating episodes, including immediately prior to volcanic eruption. These data in turn require exceedingly low crustal heat production for the Siberian craton. Low crustal heat production in the Siberian craton, and perhaps most cratons, suggests that stable continental crust may be intrinsically HPE-poor (e.g., mafic) or that HPE-rich reservoirs in the crust were removed and subsequently recycled back into the mantle.