Radiogenic heat production provides a thermal threshold for Archean cratonization process

Abstract

A striking feature of the Yilgarn craton at the current erosional level is an abundance of late K-rich granites with radiogenic heat production elevated far above global crustal averages. Extrapolated back in time, the total thickness and contribution to crustal heat production and heat flow from these granites were greater, implying that the deeper crustal sources must also have had elevated radiogenic heat production. Through back-calculated and time-integrated one-dimensional thermal modeling underpinned by geological and geochemical constraints for the model crustal columns, we find that elevated radiogenic heat production provided a significant internal driver for prolonged crustal melting and eventual cratonization of the Yilgarn craton. Our results show that elevated thermal gradients driven by high heat production thermally primed the mid- and deep crust at or above the threshold for large-volume partial melting over long periods of time, as evidenced in the magmatic rock record. This would have been amplified by any additional heat that may have been provided by the mantle melting processes that punctuated the geological history. Over time, advective movement of progressively more radiogenic heat production to the shallower crust would have resulted in two complementary outcomes: progressively refractory deep crust and long-term cooling. The widespread granite “bloom” at 2650−2600 Ma records the final time at which the crust was fertile enough to melt in large volumes and the thermal gradient was hot enough to intersect the solidus. The magnitude of radiogenic heat production in the Yilgarn craton has been underestimated in previous studies, resulting in an underappreciation of the importance of its contribution to internal drivers of magmatism and ultimately cratonization.