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oa How Can the South Atlantic Spreading Rate Vary so Quickly?
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 76th EAGE Conference and Exhibition 2014, Jun 2014, Volume 2014, p.1 - 3
Abstract
The spreading history of the South Atlantic Ocean is characterized by large spreading rate variations over short (10–15 Myrs) timescales, with fast spreading in Late Cretaceous and Eo-Oligocene. These variations are kinematically well constrained, but their dynamic origin is still unknown. Using simple tectonic force balance models and fluid-dynamic scaling arguments we show that the spreading rate variations require a significant decoupling from the lower mantle buoyancy distribution via a thin and low-viscosity asthenosphere. Moreover, we show that basal drag due to Poiseuille flow in the asthenosphere is a major component of the tectonic force balance. An unsteady asthenospheric flow due to temporal changes in regional pressure gradients can thus explain the spreading rate history, but also implies a correlation of horizontal and vertical motions: the lateral pressure gradients that drive the asthenospheric flow are also bound to cause a conspicuous non-hydrostatic topography gradient across the basin. We find that this prediction from our models agrees with a broad range of geologic and geophysical observations of the South Atlantic region, including episodes of passive margin uplift, regional basin reactivation and magmatic activity.
