Combining 2D-basin and structural modelling to constrain heat transport along the Muroto Transect, Nankai Trough, Japan

The Nankai Trough located southeast of Shikoku Island, Japan, exhibits a zone of exceptionally high heat flow. In the central part of the Nankai Trough the fossil spreading centre of the Shikoku Basin is subducted beneath the southwest Japan arc. We have modelled the temperature and maturation history along the Muroto Transect reaching from the tip of the thrust zone out into nearly undeformed Quaternary and Tertiary sediments seawards of Nankai Trough. We used two balanced cross-sections defining the sections before and after overthrusting as input for 2D-basin modelling. We can show that rapid burial and overthrusting during the Quaternary in combination with a heat flow history following the cooling curve of a 15 Ma old oceanic plate is not sufficient to explain the measured maturity of organic material in the sediments. Several heat flow scenarios derived from theoretical concepts [Yamano, M., Kinoshita, M., Goto, S., Matsubayashi, O., 2003. Extremely high heat flow anomaly in the middle part of the Nankai Trough. Physics and Chemistry of the Earth, Parts A/B/C 28, 487–497.] and previous modelling approaches [e.g. Brown, K.M., Saffer, D.M., Bekins, B.A., 2001. Smectite diagenesis, pore water freshening, and fluid flow at the toe of the Nankai wedge. Earth and Planetary Science Letters 194, 97–109; Spinelli, G.A., Underwood, M.B., 2005. Modeling thermal history of subducting crust in Nankai Trough: constraints from in situ sediment temperature and diagenetic reaction progress. Geophysical Research Letters 32(L09301): doi:10.1029/2005GL022793; Steurer, J., Underwood, M.B., 2003. Clay mineralogy of mudstones from the Nankai Trough reference sites 1173 and 1177 and frontal accretionary prism site 1174. In: H. Mikada et al. (Eds.), pp. 1–37. Available from: ] were tested. The best match between observed maturity levels, temperature and heat flow measurements is reached for a heat flow history which initially assumes the cooling of a 15 Ma old oceanic lithosphere but is reheated to 170–180 mW/m2 during the phase of rapid burial in the Quaternary. This can be achieved either by assuming the onset of hydrothermal circulation in the cooling crust or by reheating caused by off-axis volcanism at about 6 Ma [Yamano, M., Kinoshita, M., Goto, S., Matsubayashi, O., 2003. Extremely high heat flow anomaly in the middle part of the Nankai Trough. Physics and Chemistry of the Earth, Parts A/B/C 28, 487–497.].