Continental rifting as a function of lithosphere mantle strength

The role of the uppermost mantle strength in the pattern of lithosphere rifting is investigated using a thermo-mechanical finite-element code. In the lithosphere, the mantle/crust strength ratio (S-M/S-C) that decreases with increasing Moho temperature T-M allows two strength regimes to be defined: mantle dominated (S-M > S-C) and crust dominated (S-M < S-C). The transition between the two regimes corresponds to the disappearance of a high strength uppermost mantle for T-M > 700 degrees C. 2D numerical simulations for different values of S-M/S-C show how the uppermost mantle strength controls the style of continental rifting. A high strength mantle leads to strain localisation at lithosphere scale, with two main patterns of narrow rifting: coupled crust-mantle at the lowest T-M values and deep crustal decollement for increasing T-M values, typical of some continental rifts and non-volcanic passive margins. The absence of a high strength mantle leads to distributed deformations and wide rifting in the upper crust. These numerical results are compared and discussed in relation with series of classical rift examples. (c) 2008 Elsevier B.V. All rights reserved.