Relicts of mud diapirism of the emerged wedge-top as an indicator of gas hydrates destabilization in the Manila accretionary prism in southern Taiwan (Hengchun Peninsula)

Abstract

Due to oblique collision of the Luzon Volcanic arc and Eurasian passive margin, in Taiwan we observe southward progression of mountain building processes. Consequently, the southernmost tip of Taiwan represents the most recently emerged part of the orogen - the Hengchun Peninsula. The area shows evidence of a trench-slope basin that emerged in the Holocene with landforms that bear submarine characteristics. In the Late Pleistocene, lagoonal sediments blanket the basin, however the deeper deposits (Maanshan Formation) can be found on the surface in several areas. We document that the Maanshan Formation was brought to the surface through upwelling structures—mud diapirs—as a consequence of fast and overpressured sedimentation from the emerging orogen. Although fast erosional processes continuously reorganize the new landscape, we are able to capture relicts of fast eroding inactive mud volcanoes. These unique features are preserved on the surface due to shielding by coral terraces during the shallowing and the lagoonal period of the basin. Stable carbon δ13C and oxygen δ18O isotope analysis, performed on samples of carbonate blocks of cold vents collected on the outcrops of the Maanshan Formation, confirm classic seep carbonates origins. We also identify a mud-core anticline below the study area acting as the main source for the mud volcanoes and a possible cause of the uplift of the trench-slope basin. Two multichannel seismic profiles from marine surveys along with a synthesis of several previous surveys helped construct a model of the characteristics of mud diapirism in southeastern offshore Taiwan.