Abstract
Surface processes and magmatism condition the structural evolution of continental rifts and passive margins through mechanical and thermal effects on the lithosphere rheology. However, their inter-relationships in extensional settings are largely unknown. Here, I use coupled thermo-mechanical geodynamic and landscape evolution numerical modeling to assess the links between erosion of rift shoulders, sedimentation within the rift basin and extensional rock melting. Results suggest that, when the crust is thinner than ~40 km, the extension rate is slower than ~2 cm/yr and the mantle potential temperature is below ~1230 °C, efficient surface processes may double crustal melting by Moho lowering and inhibit mantle decompression melting by ~50% through sediment loading within the rift basin. It is thus likely that surface processes significantly influenced the magmatic activity of a number of extensional settings worldwide – e.g. the Mediterranean, the Gulf of California, the Iberia-Newfoundland margin, and the South China Sea. Because magmatism and surface processes affect jointly the geological carbon cycle, the surface processes forcing on extensional rock melting investigated here involves an additional means of linkage between plate tectonics and climate changes.
Highlights
Surface processes and magmatism condition the structural evolution of continental rifts and passive margins through mechanical and thermal effects on the lithosphere rheology
The details and timing of the model evolution depend upon the assumed thermal and mechanical parameters, but the overall sequence of events, coherent with that of “type II” continental rifts following the classification of ref. 60 is robust and includes: (1) lithospheric stretching, early breakup of the mantle lithosphere and asthenospheric upwelling to Moho depths, (2) prolonged crustal stretching to continental breakup and oceanization between the two newly formed continental passive margins
The topography produced by the model is consistent with that of rift flanks and basins observed in natural case studies, where the rift basin is filled at the expenses of the eroded rift shoulders (Figs. 4 and 5)
Summary
Surface processes and magmatism condition the structural evolution of continental rifts and passive margins through mechanical and thermal effects on the lithosphere rheology Their interrelationships in extensional settings are largely unknown. Magma-poor rifted margins are characterized by wide domains of extended lithosphere with local magmatic bodies intruding syn-rift and especially post-breakup units[10,15,16] In both cases, because the stresses required to rupture a typical continental lithosphere are estimated to be higher than those generated by extensional tectonics[17,18], lithospheric heating/weakening and magma production likely provide a substantial contribution to lithospheric rupturing[19,20,21]. Climate changes at geological timescales[42,43] and climate exerts a primary control on surface processes[27], assessing likely relationships between surface processes and rock melting in rifting contexts is timely and key to our understanding of the geological carbon cycle and the surface-deep Earth processes coupling[44]
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