Scale of heat flow variations in the Canadian Shield: Implications for the deep structure of the lithosphere
Abstract
We compare the two end-member models have been proposed to explain the variations in surface heat flow in stable continents. These models call for changes of either crustal heat production or heat flow at the base of the lithosphere. We show that the scale of the surface heat flow variations controls how these variations affect the thermal structure and thickness of the lithosphere, and provides constraints on these models.
We have used the data from the Canadian Shield and the Appalachians that are now extensive enough to address problems of scale and relationship between average heat flow and heat production. We have analyzed the global data set as well as data from five compositionally distinctive subprovinces where a meaningful average could be calculated. Within each province, on scales < 500 km, observed heat flow variations are linked to changes of local crustal structure. For the five subprovinces, the average values of heat flow (/line{Q}) and heat production (/line{A}) conform to the simple relationship /line{Q} = Qo + H /line{A}, where H ≈ 9km and Qo ≈ 33 hfu. This shows that, on scales larger than the dimensions of these provinces (> 500 km), there is no variation in basal heat flow and hence that variations in crustal heat production dominate. The large heat flow step at the Grenville-Appalachian boundary (≈ 16 hfu) may be accounted for by a change in crustal heat generation only. In that case, the lithosphere is ≈ 50km thinner in the Appalachians than in the Shield. At wavelengths of 500 km or more, mantle heat flow variations are constrained to be smaller than the detection limit of heat flow studies, or about ± 2 hfu. Such variations imply temperature differences which may be as large as 400 K at 150 km depth, which are consistent with seismic shear wave velocity variations and geothermobarometry studies on mantle xenoliths.- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2004
- Bibcode:
- 2004AGUSM.T21A..08M
- Keywords:
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- 1020 Composition of the crust;
- 8120 Dynamics of lithosphere and mantle: general;
- 8130 Heat generation and transport