11:15 AM - 11:30 AM
[SCG45-09] Heat flow anomaly in the southern part of Okinawa Trough – A preliminary result from the KH-21-3 cruise-
Keywords:Okinawa Trough, Heat flow, IODP
The southern part of Okinawa Trough, located between Ryukyu Islands and the East China Sea, has been extending since ~10 Ma. In its middle is a central graben, called the Yaeyama Rift (YR), bounded by a series of E-W trending normal faults. Previous seismic refraction surveys reveal a thick (~15 km) crust, indicating that the southern Okinawa Trough is in a continental rifting stage having extension/subsidence.
One of the key observations to test this hypothesis is the heat flow. However, so far very little data exist here, except for some very low heat low within YR. During the KH-21-3 cruise Leg 1, 17 new heat flow data were obtained as well as seismic reflection survey, piston coring, bathymetry and dredge sampling in the southern part of Okinawa Trough (Figure).
Obtained temperature vs. depth profiles are all linear, supporting a thermal conduction dominant near the surface. Thermal conductivity values, measured on piston core samples, are generally close to 1 Wm-1K-1, typical of surface marine sediments.
Preliminary heat flow values vary greatly from < 40 mWm-2 to 120mWm-2, suggesting local-scale excursions ongoing at the sites. Low heat flow in the southern slope of YR can either be due to rapid sedimentation or to the recharge od seawater in the hydrothermal system.
At site HF2, we conducted 8 measurements. It is located between the Ishigaki Knoll and the Yaeyama Knoll, where a bathymetric swell and subseafloor ‘melt lens’ are identified by Arai et al. (2016 JGR), called the ‘magmatic uplift’. Through the multi-narrow bathymetric survey we identified two seamount aligned E-W with their height ~100 m. HF2 measurements were made along E-W line running in the northern rim of the western seamount. Surprisingly the heat flow increases eastward. The eastern most point is located between two seamounts, and has the highest value 120 mWm-2. The seismic reflection profiles show anomalous reflection beneath the seamounts, implying the relation with the magmatic uplift by Arai et al.
The purpose of this leg is to get new data for the IODP drilling proposal. As such, it is necessary to show the regional heat flow in the south Okinawa Trough. Because of large scatter in heat flow, so far we cannot show the regional heat flow in this area. The southern most site shows 70mWm-2 (PC4), but this site may also be disturbed by the turbidites supplied from south. However, the finding of twin seamounts and heat flow anomaly should give us a new insight on the evolution of Okinawa Trough.
One of the key observations to test this hypothesis is the heat flow. However, so far very little data exist here, except for some very low heat low within YR. During the KH-21-3 cruise Leg 1, 17 new heat flow data were obtained as well as seismic reflection survey, piston coring, bathymetry and dredge sampling in the southern part of Okinawa Trough (Figure).
Obtained temperature vs. depth profiles are all linear, supporting a thermal conduction dominant near the surface. Thermal conductivity values, measured on piston core samples, are generally close to 1 Wm-1K-1, typical of surface marine sediments.
Preliminary heat flow values vary greatly from < 40 mWm-2 to 120mWm-2, suggesting local-scale excursions ongoing at the sites. Low heat flow in the southern slope of YR can either be due to rapid sedimentation or to the recharge od seawater in the hydrothermal system.
At site HF2, we conducted 8 measurements. It is located between the Ishigaki Knoll and the Yaeyama Knoll, where a bathymetric swell and subseafloor ‘melt lens’ are identified by Arai et al. (2016 JGR), called the ‘magmatic uplift’. Through the multi-narrow bathymetric survey we identified two seamount aligned E-W with their height ~100 m. HF2 measurements were made along E-W line running in the northern rim of the western seamount. Surprisingly the heat flow increases eastward. The eastern most point is located between two seamounts, and has the highest value 120 mWm-2. The seismic reflection profiles show anomalous reflection beneath the seamounts, implying the relation with the magmatic uplift by Arai et al.
The purpose of this leg is to get new data for the IODP drilling proposal. As such, it is necessary to show the regional heat flow in the south Okinawa Trough. Because of large scatter in heat flow, so far we cannot show the regional heat flow in this area. The southern most site shows 70mWm-2 (PC4), but this site may also be disturbed by the turbidites supplied from south. However, the finding of twin seamounts and heat flow anomaly should give us a new insight on the evolution of Okinawa Trough.