[S26-2] Exploring connections between heat flow and tectonics II

[S26-2-01] Heat flow distribution along the Nankai Trough floor correlated with the crustal structure of the incoming oceanic plate

^○Makoto Yamano¹, Yoshifumi Kawada², Mikiya Yamashita³ (1.The University of Tokyo, Tokyo, Japan, 2.Tohoku University, Sendai, Japan, 3.JAMSTEC, Yokohama, Japan)

Detailed heat flow measurements conducted on the floor of the Nankai Trough, near the trench axis, revealed that the heat flow distribution significantly varies along the trough. The variation appears to be correlated with the spreading history of the incoming Philippine Sea plate (Shikoku Basin). In the central part of the trough (between 134.5 and 136 degE), the youngest part pf the Shikoku Basin formed by spreading in the NE-SW direction, heat flow is highly variable and the average is much higher than the value estimated from the seafloor age. In the older parts of the basin formed by E-W spreading with a faster rate, located on the east and on the west of the central part, heat flow is nearly normal and less scattered. Other geophysical data, e.g., seismicity, crustal thickness, and basement topography, also vary significantly around the spreading direction boundaries. It suggests that the crustal structure changes across the boundaries associated with differences in the spreading direction and rate. The high average heat flow in the central part of the trough floor can be attributed to heat transport along the plate interface by fluid circulation through a permeable layer in the subducted oceanic crust (Spinelli and Wang, 2008). The permeability structure of the crust may be different between the central part and the older, eastern and western parts, resulting in difference in intensity and/or pattern of fluid circulation, and thus the observed contrasting heat flow. The high variability of heat flow in the central part may also be related to the crustal structure. In the central part, characterized by large basement relief, there is a negative correlation between heat flow and sediment thickness; higher heat flow on basement highs, whereas no apparent correlation is found in the eastern and western parts. These findings indicate that the crustal structure of the Shikoku Basin has a large influence on the temperature distribution along the plate interface.