Mechanics of basin inversion

The long-term consequences of rifting for the thermal state of the deep cru st and upper mantle reflect, in part, cooling induced by the reduction in h eat production in the attenuated lithosphere and heating due to the burial of this heat production beneath the basin. Provided that the heat productio n is largely concentrated in the upper half of the crust, these factors res ult in significant increases in temperature at deep crustal and upper mantl e levels. Because the Moho depth is likely to be reduced in the long-term L imit of an isostatically balanced basin, these same factors may lead to sli ght cooling or slight heating of the Moho, depending on the nature of the b asin-fill. For a Brace-Goetze lithospheric rheology (i.e. a rheology govern ed by a combination of frictional sliding and power-law creep), significant long-term Lithospheric weakening (up to 5% per kilometre of basin-fill) ac companies basin formation when the lower crust is initially relatively stro ng and the basin fill is characterised by appreciable heat production and l ow thermal conductivity. In contrast, initially weak lower-crustal rheologi es may result in long-term lithospheric strengthening. Evidence for basin-i nversion in the geological record may therefore imply that heat production is strongly concentrated in the upper half of the crust and, under normal c ontinental thermal regimes, the lower crust is strong. (C) 1999 Elsevier Sc ience B.V. All rights reserved.