HEAT-FLOW, GRAVITY AND STRUCTURE OF THE ABITIBI BELT, SUPERIOR PROVINCE, CANADA - IMPLICATIONS FOR MANTLE HEAT-FLOW

The results of new heat flow measurements are presented for eleven sites located in the Abitibi greenstone belt of the Archean Superior Province. These new and previously published heat flow data are used with gravity and seismic data to constrain the crustal structure and composition of the Abitibi subprovince, and to determine the mantle heat flow beneath the Canadian Shield. In order to analyze the long-wavelength variations in heat flow and Bouguer gravity anomaly, the crust was divided into three layers with distinctive composition and physical properties. Average density, heat production and thickness for each layer were varied within a range compatible with measurements and yielded crustal models consistent with gravity and heat flow data. The dominant contribution to crustal heat production is that of a tonalitic type layer which has the lowest density. The models require mantle heat flow to range between 10 and 14 mW m-2. The westward increase in heat flow requires the tonalitic layer to thicken from the Grenville Front toward the Kapuskasing uplift at the expense of the greenstone supracrustals. Long-wave-length gravity data are more affected by changes in crustal thickness than by composition, and the low Bouguer anomaly near the eastern Grenville Front is caused by 5-6 km of crustal thickening. In greenstone terranes, the long-wavelength variations in heat flow are more useful for determining average crustal composition and the thickness of supracrustals than the gravity data.