Effect of near-ridge thermal anomalies on the subsidence of the oceanic lithosphere : Constraints from a 2-D dynamic model

A 2-D dynamic cooling model with temperature-dependent asthenosphere viscosity is devised to examine the impact of near-ridge thermal anomalies on the subsidence of the oceanic lithosphere. In this model, mid-ocean ridge segments with cooler than ambient mantle temperatures have calculated subsidence rates that cannot be differentiated from normal ridge segments. This occurs because the cooler thermal anomaly cannot be sustained, nor can it spread off-axis, due to thermally driven near-ridge buoyant flow. When the cooler anomaly is deeply rooted, this buoyant flow can be inhibited only when the asthenosphere viscosity is as high as 3×1020 Pa-s. On the other hand, ridge segments with warmer mantle temperatures have significantly higher subsidence rates than those predicted from standard conductive cooling models. Simply varying the injection temperature invalidates the 1-D simplification usually invoked implicitly in models of the cooling process of the oceanic lithosphere.