Surface heat flow, crustal temperatures and mantle heat flow in the Proterozoic Trans‐Hudson Orogen, Canadian Shield

Abstract

The Paleo‐Proterozoic (1.8 Ga) Trans‐Hudson Orogen (THO), of intermediate age between the Superior (2.7 Ga) and Grenville (1.0 Ga) provinces, is located near the center of the Canadian Shield. We report on new measurements of heat flow and radiogenic heat production in 30 boreholes at 17 locations in this province. With these data, reliable values of heat flow and heat production are available at 45 sites in the THO. The mean and standard deviation of heat flow values are 42 ± 9 mW m−2. In this province, distinctive geological domains are associated with specific heat flow distributions. The heat flow pattern follows the surface geology with a central area of low values over an ancient back arc basin (Kisseynew) and an ancient island arc (Lynn Lake Belt) made of depleted juvenile rocks. Higher heat flow values found in peripheral belts are associated with recycled Archean crust. Within the Canadian Shield, there is no significant variation in heat flow as a function of age between provinces spanning about 2 Gyr. There is no geographic trend in heat flow across the Canadian Shield from the THO to the Labrador Sea. Low heat flow areas where the crustal structure is well‐known are used to determine an upper bound of 16 mW m−2 for the mantle heat flow. Present and paleogeotherms are calculated for a high heat flow area in the Thompson metasedimentary belt. The condition that melting temperatures were not reached in Proterozoic times yields a lower bound of 11–12 mW m−2 for the mantle heat flow.

Low heat flux and large variations of lithospheric thickness in the Canadian Shield

“…Window A in the Proterozoic Trans-Hudson Orogen contains only areas of juvenile crust, and excludes data from the Thompson belt adjacent to the Superior Province and from the Snow Lake-Flin Flon belt. The former is made of enriched sediments deposited in an ancient continental margin at the western edge of the Superior Province whereas the latter is underlain by radiogenic basement of the small Archean Sask craton [Rolandone et al, 2002]. The Thompson belt is narrow and associated with a local heat flux anomaly that does not affect temperatures deep in the lithosphere.…”

“…Moho heat flux values of 10-15 mW m −2 have thus been derived for the Grenville Province, east of the western Superior [Pinet et al, 1991], and for the Trans-Hudson Orogen (THO) to the west [Rolandone et al, 2002]. A key point is that, over a single geological province such as the Abitibi belt for example, the Moho heat flux cannot change significantly, for reasons that have been detailed in section 3.2.…”

“…From laboratory measurements on samples from the Superior Province, Durham et al [1987] derived a relationship between thermal diffusivity, temperature, and the quartz content of rocks. Assuming constant density and specific heat throughout the crust, Rolandone et al [2002] used these results to derive the following relationship between the lattice thermal conductivity and the temperature:…”

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

“…This temperature dependence must be taken into account to calculate accurate geotherms. We adopt the relationship between lattice conductivity and temperature described by Rolandone et al [2002]:…”

Thermal isostasy and deformation of possible paleoshorelines on Mars

“…In any case, heat flow variations on old and tectonothermally stable terrestrial continental regions can be as high as a factor of $1.5-2 (e.g., Cermak, 1993;Roy and Rao, 2000;Rolandone et al, 2002). If local variations of surface heat flow of at least similar amplitude existed in Mars during any moment of its history, then our results indicate that differential thermal isostasy should result in deformation of and deviation from an equipotential surface along putative paleoshorelines.…”