Regional heat flow pattern and lithospheric geotherms in northeastern British Columbia and adjacent Northwest Territories, Canada

Abstract

A new heat flow map has been constructed for northeastern British Columbia, using log-heading temperature records corrected for drilling disturbance, at depths ranging from 200 m to over 4000 m. Geothermal gradient varies from 20 to 90 mK/m (ºC/km). A significant regional trend of southward and southwestward decrease of geothermal gradient is observed in the map area. Effective thermal conductivity, based on an analysis of an evenly distributed network of wells throughout the area, shows variation in the range 1.2 to 2.4 W/mK. Very large variations of terrestrial heat flow, from 40 to 130 mW/m 2 , suggest a large imprint of highly variable heat generation in the upper crust. The lowest heat flow is observed in the southern part of the study area and especially in the southwest. The highest heat flow is in the north, with values commonly exceeding 100 mW/m 2 . However, lower heat flow values (<60 mW/ 2 ) are also observed in the north. In the deep western part of the basin, low heat flow in the south contrasts with high heat flow north of 59ºN. Reduced (deep) heat flow in the north is probably 10 to 20 mW/m 2 higher than the average of 33 mW/m 2 proposed previously. Higher regional reduced heat flow and higher than average heat generation (2-4 µW/m 3 ) of the basement rocks likely accounts for part of the northern high heat flow. It is estimated that the average temperature at a depth of 5 km is 180ºC; however, temperatures as high as 140 ºC are recorded at the much shallower depth of 2 km in the northern and northeastern part of the study area. RÉSUMÉUne nouvelle carte de flux de chaleur a été réalisée pour le nord-est de la Colombie Britannique, en utilisant les records de températures tels qu'affichés sur les titres de diagraphie et corrigés en fonction des perturbations de forage, à une profondeur allant de 200 m à plus de 4000 m. Le gradient géothermique varie de 20 à 90 mK/m (ºC/km). Sur la région cartographiée, une direction préférentielle significative régionale, orientée vers le sud et le sud-ouest, indique une diminution du gradient géothermique. Une conductivité thermique effective, basée sur l'analyse d'un réseau de distribution uniforme de puits à travers cette région, indique une variation allant de 1.2 à 2.4 W/m K. De très grandes variations de flux de chaleur terrestre de 40 à 130 mW/m 2 , suggèrent une grande empreinte d'une chaleur générée à haute variabilité sur la croûte supérieure. Le flux de chaleur le plus bas est observé dans la partie sud de la zone étudiée, et plus particulièrement dans la zone du sud-ouest. Le plus haut flux de chaleur se manifeste au nord, avec des valeurs excédant généralement 100 mW/m 2 . Cependant, les plus basses valeurs de flux de chaleur (<60 mW/ 2 ) sont également observées au nord. Dans la partie profonde située à l'ouest du bassin, le flux bas de chaleur au sud contraste avec le flux haut de chaleur au nord du 59ºN. Un flux réduit (profond) de chaleur dans le nord est probablement de 10 à 20 mW/m 2 plus fort que la moyenne de 33 mW/m 2 proposée précédemment. De...

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