Abstract
Detailed heat flow measurements were carried out around the ODP contingency drilling site KS-l (24°48'N, 122°30'E) located on the southern slope of the southwestern end of the Okinawa Trough. A total of 26 heat flow values were obtained. Within about 10 km of the site, the heat flow is lower than 50 m W/m2. Heat flow increases southward to about 65 m W/m2 on the south edge of the trough. Due to the extraordinarily high sedimentation rates, the sedimentation-corrected heat flow values have increased by as much as 76%, so only the most recent surface sedimentation effects are considered. Distribution of heat flow patterns shows that high heat flow values are associated with igneous activities and are observed in both the northern and southern flank and the western end of the Okinawa Trough. Heat flow values in the E- W trending central rift zone, on the other hand, appear to be lower. This is probably due to hydrothermal activities in the rift zone. The correlation between the heat flow and bathymetric contours is discernable, but with a slight southward shift in the heat flow pattern. Considering the fact that abnormally high and low heat flows are observed near volcanic intrusions, extrusions and faults, and that much higher heat flows would be expected if the full sedimentation effects were eliminated, we suggest that the magma associated with the extension of the southwestern Okinawa Trough has at least extended into the southwestern end of the Okinawa Trough, in northeast Taiwan.
Highlights
The Okinawa Trough is a curved backarc basin which is convex to the southeast, and located behind the Ryukyu Trench and Ryukyu Islands
The bending of the Okinawa Trough at its southwestern end is due to the collision between the Luzon volcanic arc riding along the western edge of the Philippine Sea plate and the passive continental margin of the Eurasian plate
Seismic refraction profile shows that the southern Okinawa Trough is still in a continental rifting stage and the extent of oceanic crust is restricted to the trough axis (Hirata et al 1991)
Summary
The Okinawa Trough is a curved backarc basin which is convex to the southeast, and located behind the Ryukyu Trench and Ryukyu Islands. A major ocean current, the Kuroshio (Black Current), passes through the passage between Taiwan and the southernmost part of the Ryukyu Island Arc and flows northeastward along the Okinawa Trough (Ono et al 1987) It is the biggest western boundary surface current in the western Pacific and plays an important role in the meridional transport of heat, mass, momentum and moisture from the western Pacific warm pool to the high latitudes of the North Pacific. The purpose of this paper is to provide the results of recent heat flow measurements at and in the vicinity of the KS-1 drilling site (Fig. 1), and to establish the thermal characteristics at the southwestern end of the Okinawa Trough. This study can provide more information to help understand their thermal interaction
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