Submarine hydrogeology of the Hawaiian archipelagic apron: 1. Heat flow patterns north of Oahu and Maro Reef

Abstract

We present two profiles of collocated single‐channel seismic reflection and heat flow determinations across the Hawaiian flexural moat: one north of Oahu and the other north of Maro Reef. Seismic reflection data are used as an aid in determining depth to basement and interpreting moat stratigraphy. Moat sediments are locally up to 2 km thick and result mostly from slumps, debris avalanches and turbidites from volcanoes capping the Hawaiian Ridge. Each heat flow profile is ∼200 km long and consists of paired thermal gradient and conductivity measurements made at an interval of 1–2 km. The mean heat flow, unconnected for the cooling effect of sedimentation, along the Oahu profile is 63.9 mW m−2 (s.d. 11.9 mW m−2) and along the Maro Reef profile is 59.8 mW m−2 (s.d. 5.0 mW m−2). Our preferred sedimentation correction model gives a corrected heat flow mean along the Oahu profile of 74.2 mW m−2 (s.d. 14.6 mW m−2) and for the Maro Reef profile of 64.0 mW m−2 (s.d. 4.9 mW m−2). These values are not significantly different despite the fact that oceanic crust at Maro Reef is 19 Myr older than at Oahu. The mean heat flow along the Oahu profile is within one standard deviation of the global mean value for oceanic crust of the same age, while the mean heat flow along the Maro Reef profile differs by greater than one standard deviation for the global mean. However, the mean heat flow along the Maro Reef profile is within the uncertainty of previous heat flow determinations made offswell at Maro Reef [Von Herzen et al, 1989]. Variability along each profile is significantly greater than the measurement uncertainty (measurement uncertainty is 3 and 2 mW m−2 for the Oahu and Maro Reef profiles, respectively) and is significantly greater along the Oahu profile than the Maro Reef profile. While this variability could result from fluid flow within the archipelagic apron or underlying crust, simple moat‐wide circulation models do not appear to explain the dominant variability in heat flow. Heat flow means and variability of both profiles are inconsistent with simple conductive models of lithospheric reheating.