242-13 The role of crustal thickness in governing heat-producing element distribution and cratonization

Abstract:

As much as sixty percent of today's continental crust consists of cratons that have remained stable at Earth's surface for over 2.5 billion years. The long-term stability of these cratons cannot be maintained without a cold lithospheric thermal state, which is governed not only by the total heat production within the crust but also by the vertical distribution of heat-producing elements (HPEs). Through analysis of a global geochemical database of arc magmatism, we show that crustal thickness exerts a first-order control on HPE concentrations in these building blocks of the modern continental crust and thus the vertical HPE distribution within the continental crust. Thicker crust, which drives more extensive magmatic differentiation, preferentially concentrates K, Th, and U in the upper crust and depletes the lower crust. The extent of enrichment can be related to crustal thickness as: , where A is the surface heat production and  represents the heat production expected for an undifferentiated, primitive composition. Thermal modeling demonstrates that this vertical stratification reduces lower crustal temperatures by hundreds of degrees compared to an undifferentiated crust of equivalent thickness. Extrapolating back to the Archean, higher heat production and orogenic thickening generated basal temperatures high enough for widespread lower crustal melting. The upward migration of these crustal melts, together with initial magma differentiation, concentrates HPEs in the upper crustal layers, which are subsequently eroded away owing to the high topography resulting from isostatic adjustment to crustal thickening. Through this preferential differentiation and denudation, the thickened lithosphere starved itself of heat production, progressively cooled and strengthened into the cold, rigid cratons seen today. These results indicate that crustal thickening may be a necessary step in the formation of long-term stable cratons.

Geological Society of America Abstracts with Programs. Vol. 58, No. 5, 2026

doi: 10.1130/abs/2026AM-16055

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