Analysis of heat flow data—correlation of thermal resistivity and shock metamorphic grade and its use as evidence for an impact origin of the Brent Crater

Abstract

Measurements of heat flow and radioactive heat generation values have been made at small intervals using a completely cored, 1 km deep borehole located close to the center of the Brent Crater. A remarkable correlation is observed between the thermal resistivity values and shock metamorphic grade. This is interpreted as due to residual shock effects on the lattice conductivity. These effects are preserved over long periods of time, probably because of rapid cooling that prevented thermal annealing and recrystallization. The highly shock metamorphosed samples also have characteristically low heat production values, resulting from a depletion of thorium and uranium; potassium distribution is fairly uniform except at the boundaries of metamorphic zones, where it is enriched to a considerable degree. These results support the meteorite impact hypothesis for the origin of the crater.Mean heat production and corrected heat flow values obtained for this borehole are 1.51 ± 0.57 μWm−3 (3.6 ± 1.4 HPU) and 41.9 ± 6.3 mWm−2 (1.00 ± 0.15 HFU), respectively. These values indicate that this region may belong or be similar to the Central Stable region heat flow province.