A synthesis of heat flow determinations and thermal modeling along the Nankai Trough, Japan

Abstract

[1] We review marine heat flow data along the Nankai Trough and show that observations >30 km seaward of the deformation front are 20% below conductive predictions (129-94 mW m À2 ) but consistent with the global heat flow average for oceanic crust of the same age (16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28). Heat flow values ≤30 km seaward of the deformation front are generally 20% higher than conductive predictions. This heat flow pattern is consistent with the advection of heat by fluid flow in the subducting oceanic crust and explains both the high heat flux in the vicinity of the trench, >200 and >140 mW m À2, and steep landward declines to values of approximately 60 mW m À2 over distances of 65 and 50 km along the Muroto and Kumano transects, respectively. Along the Ashizuri transect, the lack of heat flow data precludes a definitive interpretation. We conclude that fluid flow in the subducting oceanic crust leads to temperatures that are generally 25 C higher near the toe of the margin wedge and 50-100 C lower near the downdip limit of the seismogenic zone than estimated by purely conductive models.Citation: Harris, R., M. Yamano, M. Kinoshita, G. Spinelli, H. Hamamoto, and J. Ashi (2013), A synthesis of heat flow determinations and thermal modeling along the Nankai Trough, Japan,

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“…The surface heat flux consistently exceeds 100 mW/m 2 in this region and amounts to ~180 mW/m 2 at Sites 1173 and 1174 but steeply declines landward of the deformation front to values of ~60 mW/m 2 and scatters largely around 82 mW/m 2 seaward in Shikoku Basin (Yamano et al, 1984;Kinoshita and Yamano, 1986;Shipboard Scientific Party, 1991;Shipboard Scientific Party, 2001b, 2001cSpinelli and Underwood, 2005;Harris et al, 2013;. In situ temperatures at the sediment/basement interface are expected to be ~110°C at Site 1173 (734 mbsf ) and ~120°-140°C at Site 1174 (1194 mbsf) based on downhole temperature measurements in the upper 300 m of these sites ( Figure F2; Shipboard Scientific Party, 2001bParty, , 2001c.…”

“…Specifically, thermal and geochemical models suggest that advective heat and fluid flow in the subducting oceanic crust are crucial for extracting and redistributing heat (Harris et al, 2013;Spinelli and Wang, 2008), whereas the accreted sediment expels fluids mainly by upward diffusive flow through a large portion of the accretionary prism . Pore water profiles did not clearly indicate active fluid flow along the décol-lement or along the frontal thrust, and fractures within the décollement zone have not been mineralized Maltman et al, 1992;Moore, Taira, Klaus, et al, 2001); however, at >400-500 mbsf, pore water freshening is detectable in Cl -concentrations that are lower than seawater values (Figures F6, F7; cf.…”

“…Figure F1. Map showing heat flow data and ODP/IODP transects and sites in the Nankai Trough (modified from Harris et al, 2013). Marine probe (circles), boreholes (stars), and bottom-simulating reflector (BSR) (small circles) are color coded by heat flow.…”

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“…Figure F1. Map showing heat flow data and ODP/Integrated Ocean Drilling Program transects and sites in the Nankai Trough (modified from Harris et al, 2013). Marine probes (circles), boreholes (stars), and bottom-simulating reflectors (BSRs) (small circles) are color coded by heat flow.…”

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“…Map showing heat flow data and ODP/Integrated Ocean Drilling Program transects and sites in the Nankai Trough (modified from Harris et al, 2013). Marine probes (circles), boreholes (stars), and bottom-simulating reflectors (small circles) are color coded by heat flow.…”