GEOMORPHOLOGY AND STRATIGRAPHIC FRAMEWORK OF THE YAP SUBDUCTION ZONE, WESTERN PACIFIC

The Institute of Oceanology under the Chinese Academy of Sciences conducted an integrated geophysical survey in the sea area near the Yap Island, western Pacific in 2015, including surveys of gravity, magnetism, seismics, multi-beam and sub-bottom profiles. Multichannel seismic and multi-beam data are mainly used to investigate the topography of major tectonic units and the stratigraphic framework in the Yap subduction zone as well as the tectonic characteristics of ridge subduction. Data suggests that the Parece Vela Basin, as the regional depositional center, is filled with young sediments for nearly 1000 meters. On the contrast, the horizontal depositional layers are hardly identified in the trench, where subduction erosion dominates. The Caroline ridge changed the tectonic characteristics of subduction zone, and influenced magmatism in the Yap arc due to its specific topography. The topography and geological structure of horst and graben in the north Yap are depicted in details. The topographic high of the Caroline ridge is supposed to bring greater bending and tension and favor the formation of the subsequent horst and graben belt. Multichannel seismic evidence has been used for interpreting the expansion of the Sorol Trough and its inferred age.