A steady state conductive geotherm for the north central Slave, Canada: Inversion of petrological data from the Jericho Kimberlite pipe

Abstract

Mantle xenoliths carried by kimberlite provide direct evidence for the rock types that constitute the roots to ancient cratons and provide critical constraints on the thermal state of the lithosphere. We derive a steady state conductive geotherm for the north central Slave craton based on published data for xenoliths from the Middle Jurassic Jericho kimberlite. The preferred model geotherm assumes a two‐layer lithosphere. The upper layer is D km thick, has constant thermal conductivity, and an exponential decrease in heat production with depth (Ao e−z/D); Ao is a fixed value based on the bedrock geology. Below D, the lithosphere has a higher, constant thermal conductivity and a constant value of radiogenic heat production (Am). Inverting the thermobarometric data produces model estimates of surface heat flow (qo) and the depth‐scale parameter (D) of 54.1 mWm−2, and 25.8 km, respectively. The value of D corresponds to the thickness of upper to middle crust as defined by seismology for the southern Slave craton. On the basis of our analysis the Slave craton is characterized by high surface heat flow, relative to other Archean cratons, which is consistent with a single field measurement from the southern Slave craton. The high surface heat flow results from the high concentrations of radiogenic heat producing elements found in Slave crustal rocks. Despite the relatively high surface flow, the underlying lithosphere is cool relative to mantle beneath the rest of North America and other Archean cratons. The model geotherm predicts a thermal gradient in the mantle (100–200 km) of between 5.0 and 3.7 (°C/km) and a mantle heat flow of 15.9–11.9 mWm−2 that is consistent with other estimates of mantle heat flow beneath Precambrian continental crust.