Structural Characteristics of Mud Diapir/Mud Volcano in an Accretionary Wedge Under Mountain Building: Connection Between Offshore and Onshore in Southwestern Taiwan

In order to better understand the structural characteristics of mud diapir/mud volcano in the accretionary wedge under influence of mountain building, we reconstruct geological cross sections onshore and offshore in Southwestern Taiwan, where represents the tectonic transition between the arc-continent collision of Eurasian plate and Philippine Sea plate and the subduction of the South China Sea and the Luzon arc. The geological cross sections onshore were reconstructed by conducting field investigations and combining borehole, gravity and seismic reflection data. The cross sections offshore were mainly interpreted from the available seismic reflection data. In the offshore area, the mud diapirs are abundant and they are structurally controlled as they aligned mostly along the major anticlines/thrusts in the accretionary wedge. We found that the mud diapirs offshore generally aligned with the onland mud volcanoes, which are located along three major anticlines that closely associated with major thrust faults: 1) the offshore mud diapir MD14 vs. the onland Tainan anticline, 2) the offshore MD12 vs. the onland Chunchou anticline, and 3) the offshore MD11 vs. the onland Banpingshan anticline. These three groups of mud diapir/anticline show asymmetric fold structure, especially MD14 and Tainan anticline, with a gentle long western limb and a steeper short eastern limb. This indicates a possible influence of tectonic compression, e.g., a backthrust beneath MD14, which agrees with the Houchiali fault interpreted in the onshore Tainan tableland.