2016 PSPA – Cristina Biete Castells – Effects of inherited continental margin structures in the south-central Taiwan fold-and-thrust belt

Orogens and fold-and-thrust belts (FTB) commonly present along-strike changes like changes in the structural architecture and/or different deformation styles. The generation and evolution of the geological architecture is primarily controlled by the presence of pre-existing structures and/or stratigraphy horizontal changes. With the idea to keep advancing in the knowledge of how this factors affect, we study the central-south Taiwan FTB.

Taiwan is an oblique Arc-continental collision between the Luzon Arc, striking N-S, and the Eurasian continental margin, striking in south Taiwan roughly E-W. This margin presents several extensional basins that now are involved in the Taiwan FTB

In this study we combine surface geology and balanced cross sections, which will help to understand the FTB, with seismic tomography and seismicity, that are used to trace structures from the continental margin offshore western Taiwan into the FTB. We use a Vp of 5.2 km/s as a proxy for the basement-cover interface

We found that the FTB includes significant along strike changes in structure and stratigraphy. Major N to S changes in seismic velocities are interpreted as basement highs and lows and these correlate with areas were changes in the structural grain of the FTB take place, including some localized variation in the strike of thrusts and folds that are evident on the map. Several seismicity clusters align along the borders of these basement blocks. We interpret this to be related with reactivation of basement structures.

Figure 1: a) Tomography of 6km depth slice showing with grey transparent rectangles the main areas with velocity changes. b) Tomography E-W sections with seismicity and main geologic structures. c) Geological map showing with grey transparent rectangles the main areas were structural and stratigraphic changes are present. d) N-S tomography section with seismicity showing a seismicity cluster at the south of a basement high. e) Block diagram showing roughly the possible structure of the basement on the fold-and-thrust belt, with gray transparent rectangles showing the areas were structural, stratigraphic, velocity and seismicity changes are.

This work is supervised by Joaquina Álvarez-Marrón and Dennis Brown (ICTJA-CSIC). Economic support has been provided through CGL2014-4377-P project funded by the Spanish Ministry of Science and Innovation. We acknowledge National Geographic Institute for providing the seismic data for the study.