Abstract

Uplift of the crust during rifting is a major problem that has been left unresolved by uniform stretching models. Various depth-dependent stretching models have been proposed to account for this, but these require decoupling of the crust and mantle and result in space problems within the mantle. A significant modification of these discontinuous nonuniform or depth-dependent stretching models is proposed here that accounts for synrift uplift and doming but does not result in these problems. The model involves continuous nonuniform stretching within a polygonal region bounded by symmetrical, outward-sloping boundaries within the mantle. This geometry results in thinning of the lithosphere below crustal regions that are less stretched or unstretched, crustal uplift resulting from asthenospheric upwelling below these regions. This in turn results in stretching factors for the mantle that are less than those for the crust, a relationship opposite to relationships derived by discontinuous nonuniform stretching models. Corollary predictions for mantle-derived heat flow within and outside regions of stretching of these two different depth-dependent models may allow them to be distinguished from each other and from regions where uniform stretching predominates.

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