The focus thermal study around the spreading center of southwestern Okinawa trough

Abstract

Voluminous hydrothermal systems are corresponding to the heat flow anomaly discovered from previous geophysical surveys in the Southern Okinawa Trough (SOT), which is an area with a high sedimentation rate supplied by the East China Sea shelf and the island of Taiwan. Our latest fifteen field measurements around the Geolin Mound (GLM) (24° 36.6 ‘N, 122° 53’E) are located at a sedimentary basin west of the Yonaguni Rift, which is nearby the southwestern tip of a NE-SW trending volcano trail in the SOT. The heat flow results illustrate a concentric decrease from 31,477 to 180 mW/m2 in a 1-km radius around the GLM, evidently proving the focus fluid migration along the major fluid conduit. The ultrahigh temperature observations revealed the existence of magmatic components in shallow sediments. Combining the subsurface profiles with the temperature fields around the GLM, a 0.16-km2 acoustic blanking area of the G1 fluid conduit was recognized from the chirp sonar image and numerous interpreted igneous reflections with fluids related features from seismic profiles. As a result, we proposed a conceptual model, which simultaneously illustrates the hydrothermal circulation pattern from the previous general surveys and the enormous thermal anomaly from current detailed measurements. The sill-to-sill feeding sedimentary basin of the GLM is capable of demonstrating the enormous thermal anomaly around the spreading center of the SOT and appropriately represents the potential hydrothermal discharge and recharge by heat flow distribution around the GLM.