Lithospheric Thickness of Volcanic Rifting Margins: Constraints From Seaward Dipping Reflectors. Issue 4 (4th April 2019) - Tian, Xiaochuan
Abstract: Seaward dipping reflectors (SDRs) are large piles of seaward thickening volcanic wedges imaged seismically along most rifted continental margins. Despite their global ubiquity, it is still debated whether the primary cause of SDR formation is tectonic faulting or magmatic loading. To study how SDRs might form, we developed the first two‐dimensional thermomechanical model that can account for both tectonics and magmatism development of SDRs during rifting. We focus here on the magmatic loading mechanism and show that the shape of SDRs may provide unprecedented constraints on lithospheric strength at volcanic rifting margins. For mapping SDRs geometries to lithospheric strength, a sequence of model lithospheric rheologies are treated, ranging from analytic thin elastic plates to numerical thick elasto‐visco‐plastic crust and mantle layers with temperature and stress‐dependent viscosity. We then analyzed multichannel seismic depth‐converted images of SDRs from Vøring and Argentinian rifted margins in terms of geometric parameters that can be compared to our model results. This results in estimates for the lithospheric thickness during rifting at the two margins of 3.4 and 5.7 km. The plate thickness correlates inversely with mantle potential temperature at these margins during rifting, as estimated by independent studies. Key Points: Develop 2‐D thermal‐mechanical models with realistic rheology to account for effects of tectonic and magmatic loads on seaward dipping reflectors (SDRs) formation Provide mappings between SDR geometries and effective elastic thickness ( T e ) analytically as well as lithospheric strength numerically Rifting Vøring and Argentinian margins have lithospheric thickness of 3.4 and 5.7 km, inversely correlated with corresponding mantle potential temperatures