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Submarine hydrogeology of the Hawaiian archipelagic apron : 2. Numerical simulations of coupled heat transport and fluid flow

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  • We perform numerical simulations of buoyancy-driven, pore fluid flow in the Hawaiian archipelagic apron and underlying oceanic crust in order to determine the extent to which heat redistributed by such flow might cause conductive heat flow measurements to underrepresent the true mantle heat flux. We also seek an understanding of undulations observed in finely spaced heat flow measurements acquired north of Oahu and Maro Reef with wavelengths of 10 to 100 km and amplitudes of 2 to 7 mW m¯². We find that pore fluid flow can impart significant perturbations to seafloor heat flow from the value expected assuming a constant mantle flux. In the simplest scenario, moat-wide circulation driven by bathymetric relief associated with the volcanic edifice recharges a fluid system over the moat and discharges the geothermally heated water through the volcanic edifice. The existing heat flow data are unable to confirm the existence of such a flow regime, in that it produces prominent heat flow anomalies only on the steep flanks of the volcano where heat flow probes cannot penetrate, However, this flow system does not significantly mask the mantle flux for reasonable permeabilities and flow rates. Another numerical simulation in which the upper oceanic basement acts as a aquifer for a flow loop recharged at basement outcrops on the flexural arch and discharged within a permeable volcanic edifice is capable of almost uniformly depressing conductive heat flow across the entire moat by ~15%. Large heat flow anomalies (>20 mW m¯²) are located over the recharge and discharge zones but are beyond the area sampled by our data. Presumably finely spaced heat flow measurements over the flexural arch could test for the existence of the predicted recharge zone. We demonstrate that the prominent, shorter-wave undulations in heat flow across the Oahu and Maro Reef moats are too large to be explained solely by relief in the upper oceanic basement. More likely, shallower large-scale turbidites or debris flows also serve as aquifers within the less permeable moat sediments. With our limited information on the structural geology of the moat, permeability structure of its major geologic units, and their variations in the third dimension, we arc not able to exactly match the. spatial distribution of heat flow anomalies in our data, hut spectral comparisons look promising.
  • Copyrighted by American Geophysical Union.
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  • Christiansen, L., Garven, G., Georgen, J., Harris, R. N., McNutt, M. K., Von Herzen, R. P. (2000), Submarine hydrogeology of the Hawaiian archipelagic apron 2. Numerical simulations of coupled heat transport and fluid flow, J. Geophys. Res., 105, B9, 21371-21385.
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  • 105
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  • B9
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