A gas hydrate site with bi-verging folding in the outer wedge offshore SW Taiwan: Results from kinematic structural modeling and finite strain analysis.

Bernal-Olaya, Rocio, Chi, Wu-Cheng, Kunath, Pascal, Sanchez, Javier, Higgs, Benjamin and Berndt, Christian (2020) A gas hydrate site with bi-verging folding in the outer wedge offshore SW Taiwan: Results from kinematic structural modeling and finite strain analysis. Tectonophysics, 790 (Article number 228540). DOI 10.1016/j.tecto.2020.228540.

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Abstract

Highlights

• We interpret the Four Way Closure Ridge (FWCR) and the Ridge A as a set of bi-vergent folds, a detachment fold and a trishear fault propagation, which formed sequentially over a strong detachment.
• We suggest a quantification of the strain compaction of Ridge A and FWCR, finding correlation of dilation and porosity lost, with the variation of the physical properties—increase in resistivity and seismic velocity—measured by Berndt et al. (2019).
• We conclude that the sourced fluids from the calculated mechanical compaction alone could not explain the observed hydrate accumulations in the FWCR. Additional sources, possibly from depth, are required.
• Using growth strata as constraints, we have conduced kinematic structural modeling and finite strain calculations. Such combination of analyses might become helpful for research on gas hydrate and other km-scale structural geology in active margins.

Abstract

Understanding the structural evolution of complex convergent plate boundaries could contribute to linking the anticipated fluid production and transportation at depth to the measured amounts of fluid stored in hydrate methane. To better understand fluid behavior within a complex convergent boundary, we propose an evolution model for a set of doubly plunging, oppositely-verging structures referred to as Ridge A and the Four-Way Closure Ridge (FWCR), located offshore southwestern Tawian. The structures exhibit 1) Initial deformation along a decollement forming a seaward (westward)-verging detachment fold, followed by 2) a landward(eastward)-verging fault propagation fold (trishear) about 8 km east of the detachment fold, and 3) a westward-verging low-angle thrusting modifying the previous structures. Furthermore, finite strain analyses based on the kinematic model suggest high pore space reduction between the detachment and fault propagation folds. The volume of methane possibly expelled during the pore space reduction is not enough to explain the high hydrocarbon concentration necessary for hydrate formation. Kinematic modeling along with finite strain analyses support the possibility of deep sourced fluid migration along such bi-vergent structures at this hydrate-rich site.

Document Type: Article
Keywords: Outer, Wedge, Methane, Hydrate, Taiwan
Research affiliation: OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-GDY Marine Geodynamics
Refereed: Yes
Open Access Journal?: No
Publisher: Elsevier
Date Deposited: 08 Jul 2020 06:52
Last Modified: 08 Feb 2023 09:28
URI: https://oceanrep.geomar.de/id/eprint/50081

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