Heat-flow variations correlated with buried basement topography on the Juan de Fuca Ridge flank

Abstract

SYSTEMATIC heat-flow variations are commonly observed on sedimented flanks of mid-ocean ridges. These variations have been attributed to the convective circulation of pore fluids within the oceanic crust, and have been used to estimate the scale and pattern of this circulation. Here we report similar systematic variations observed in a detailed heat-flow and seismic-reflection survey over sediment-covered 3-Myr-old sea floor on the eastern flank of the Juan de Fuca Ridge. We find that heat-flow peaks are located above buried basement ridges and adjacent to two minor basement outcrops; heat-flow lows are found where thick sediments fill basement valleys. The simple inverse relationship between heat flow and sediment thickness defined by the data indicates that hydrothermal circulation sealed within the permeable portion of the oceanic crust is vigorous enough to maintain approximately isothermal (±10 K) conditions at the sediment/crust interface. As no systematic variations in estimated basement temperatures are observed, it seems that at this location the heat-flow variations result only from sediment thickness variations, and do not reflect a particular convective pattern.