Heat production and thermal conductivity of rocks from the Pikwitonei-Sachigo continental cross section, central Manitoba: implications for the thermal structure of Archean crust.

The Pikwitonei and Sachigo subprovinces of central Manitoba provide a cross-sectional view of the Superior province crust. In cross section, the upper to mid-level crust is composed of synformal greenstone belts surrounded by tonalitic gneisses, both of which are intruded by granitic plutons. This crustal structure persists downwards into the granulite facies, where keels of the greenstone belts can be found. To constrain models of the crust, heat production and thermal conductivity in 60 rocks from this terrain were measured using standard gamma -ray spectrometry and divided bar techniques. Large vertical and lateral heterogeneities in heat production in the upper crust are evident; heat production is high in granites and metasedimentary rocks, intermediate in tonalite gneisses, and low in the portions of greenstone belts dominated by mafic meta-igneous rocks. -J.M.H.