Heat flow and structure of the lithosphere in the Eastern Canadian Shield

Abstract

Twenty-two new determinations of heat flow and radiogenic heat production in the Superior and Grenville provinces of the Canadian Shield are presented. The new data and previously published measurements strongly constrain the thermal structure of the eastern Canadian Shield. In the Abitibi greenstone belt, heat flow gradually increases from 29 mW m -2 near the Grenville Front to 44 mW m -2 east of the Kapuskasing uplift. This heat flow variation is interpreted in terms of crustal thickening and increased thickness of a tonalitic layer with average heat production of about 1.1 m -3. This interpretation, based on estimated heat production of major rock types in the region, is consistent with crustal models derived from recent seismic reflection and refraction studies. It also leads to an estimate of about 12 mW m-2 for the mantle heat flow beneath the area. The average heat flow in the Grenville Province, 41 +-10 mW m -2, is the same as that of the Superior Province. This similarity and the lack of significant variation of heat flow across the Grenville Front indicate that the crust on both sides of the front has similar heat production and thus composition. In the western part of the Grenville Province, heat flow reaches high values in the vicinity of the boundary between the Allochtonous Polycyclic and Monocyclic belts where enriched granitic plutons are found. In the crystalline terranes in the central part of the Grenville Province, heat flow and heat production are related to each other. The parameters of the linear •eat flow-heat production relationship (Qr = 30 +_ 2 mW m -2 and D = 7.1 +_ 1.7 km) are close to those of the much younger Appalachian Province,implying that the higher Appalachian heat flow is due solely to higher heat production in the upper crust. The data provide no evidence for variation of mantle heat flow between the Superior, Grenville, and Appalachian provinces, whose tectonic ages range between 2700 and 400 Ma. The small value of the mantle heat flow, about 12 mW m -2, implies that the depth to the 450øC isotherm, which controls the effective elastic thickness of the lithosphere, is very sensitive to crustal heat production.

Temperature and rheological properties of the mantle beneath the North American craton from an analysis of heat flux and seismic data

“…It has a high average surface heat flux (57.3 ± 5.8 mW m −2 ) and a slightly positive traveltime delay (+0.13 s). The upper crust of the Appalachians is characterized by an abundance of granites and metasediments with large U, Th, and K contents, which accounts for the elevated heat flux [Jaupart et al, 1982;Pinet et al, 1991]. This province was subjected to several recent perturbations, including the Devonian Acadian Orogeny and culminating in the intrusion of the highly enriched granite bodies of the White Mountains magma series.…”

Interprétation des données de flux de chaleur et de gravité dans le Bouclier Canadien /

“…Jessop et al (1984) ont réalisé une première synthèse des données de flux terrestre du Canada en 1984 (214 sites). A la suite, Pollack et al (1993) Référence : (1) Jessop et al, 1971; (2) Cermak et Jessop, 1971; (3) Jessop et Lewis, 1978; (4) Lewis et Beck, 1977; (5) Misener et si., 1951;(6) Drudy et Lewis, 1983; (7) Sass et ai., 1968;(S) AIBs, 1975;(9) AUis et Garland, 1979;(10) Lewis, 1969;(11) Tatlor et Judge, 1979;(12) Beck et W. Neophytou,19S8;(13) Beck et Sass, 1966;(14) Sass et al, 1971;(15) Fou, 1969;(16) Beck et Logis,19S3;(17) Jessop et al, 1984;(18) Mareschal et ai., 1989;(19) Pinet et al, 1991;(20) Guilkm et al, 1994;(21) Drury, 1991;(22) Guillou et al, 1996;(23) Mareschal et al,, 1998;(24) Guilîou et al,199S;(25) Mareschal et al, 1999;(26) …”

Water, Life, and Planetary Geodynamical Evolution

“…These variations cannot be attributed simply to geologic ages but essentially reflect the variability in concentration in radioactive elements of crustal rocks. In fact, the heat flux at the surface can be attributed in a large part to heat production in the crust and the flux from the mantle has been estimated to values of the order of 7-15 mW m −2 (Pinet et al 1991;, to be compared to the average of 100 mW m −2 of the oceans. It is then reasonable to assume the continents to be perfect insulators when modeling the thermal evolution of the Earth (Grigné and Labrosse 2001).…”