HR: 11:20h
AN: T22B-05 INVITED    [Abstracts]
TI: Heat flow, crustal heat production, and crustal evolution in the Canadian Shield
AU: * Mareschal, J
EM: mareschal.jean-claude@uqam.ca
AF: GEOTOP-UQAM-McGill, University of Quebec at Montreal, POB 8888, sta. "downtown", Montreal, QC H3C3P8, Canada
AU: Jaupart, C
EM: cj@ccr.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 Pl. Jussieu, Paris, 75252, France
AB: More than 200 heat flow values are available for the entire Canadian Shield, in provinces that range in age between >3Ga and <1Ga. Heat production has been determined at nearly all the heat flow sites. In addition, systematic heat production studies have been conducted that sample through the most important lithologies and all structural levels. At the largest scale, we find that the mean heat flow is the same 41mW~m^-2 in all provinces regardless of age, with the exception of the Archean Slave Province where the limited data set suggests that surface heat flow is higher (50mW~m^-2). The Slave Province is also characterized by high surface heat production. On the other hand, geothermobarometry on mantle xenoliths indicate lower mantle temperature in the Slave than in the Superior Province. Heat flow and xenolith data can be reconciled if variations in heat flow are accounted for by crustal heat production. Variations are found at the smaller scale of individual subprovinces with different lithologies. The southern part of the Superior Province consists of E-W trending belts with ages decreasing southwards. This age trend seems to be reflected in a progressive southward increase in heat flow in the greenstone belts. Within a single belt, variations in heat flow reflect changes in the average crustal composition, essentially the proportion of mafic to felsic rocks. In the PaleoProterozoic (1.8Ga) Trans Hudson Orogen, juvenile crust is less radiogenic and has lower heat flow (37 mW~m^-2) than the reworked Archean crust of the Thompson Belt (53mW~m^-2). Several examples of high amplitude-short wavelength variations in heat flow have been found suggesting that these variations are due to crustal sources. Different methods have been used to estimate the crustal and mantle contribution in different regions of the Shield. The range of mantle heat flow values is very narrow 11-15mW~m^-2 and within the error limits of the estimate (± 2 mW~m^-2), implying that most of the heat flow variations are accounted by crustal heat production. With such narrow range of Moho heat flow variations, we can define a differentiation index, as the ratio of the surface to the mean crustal heat production. This index is positively correlated with the surface heat flow at the time of crustal stabilization, which is consistent with high temperature in the lower crust resulting in a very differentiated crust. Consequently, temperature differences are small at the base of the crust and in the lithospheric mantle.
DE: 8103 Continental cratons
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8130 Heat generation and transport
SC: Tectonophysics [T]
MN: 2007 Fall Meeting