4.5 Article

Evolution of fracture networks and connectivity during fault-bend folding: Insights from the Sinon Anticline in the southwestern Hongseong-Imjingang Belt, Korea

Journal

JOURNAL OF STRUCTURAL GEOLOGY
Volume 155, Issue -, Pages -

Publisher

PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jsg.2021.104506

Keywords

Fracture network; Fracture connectivity; Fault -bend fold; Flexure; Strain partitioning

Funding

  1. National Research Foundation of Korea - Ministry of Science and ICT [2018R1C1B6003851]
  2. Energy & Mineral Resources Development Association of Korea - Korea government (MOTIE) (Data science based oil/gas exploration consortium)
  3. National Research Foundation of Korea [2018R1C1B6003851] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)

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This study investigates the characteristics and evolution of fold-related fracture networks in the Sinon Anticline, South Korea. The complexity of the fracture networks reflects the spatiotemporal variation in strain pattern, and their connectivity and fluid flow properties are controlled by structural positions and mechanical stratigraphy.
Crustal shortening in an elastico-frictional regime is mainly accommodated by contractional fault-fold systems with fracture networks. According to recent research, fracture networks in fold-thrust belts express complex internal strain states in response to thrusting and related folding. Furthermore, their connectivity and fluid flow characteristics likely depend on the structural positions and mechanical stratigraphy that control heterogeneous deformation processes. This study provides characteristics of fold-related fracture networks in the Sinon Anti-cline, which was formed by fault-bend folding in the southwestern Hongseong-Imjingang Belt, Korea. The fracture networks in the metamorphosed turbidites characterized by interbedded competent metasandstone layers and relatively thin incompetent schist layers have evolved through pre-, syn-, and post-folding fracturing events. Their complexity reflects the spatiotemporal variation in the strain pattern related to early layer-parallel shortening and subsequent fault-bend folding. Based on insights from detailed mapping and topological analysis of the fracture network, we conclude that strain partitioning that occurs during flexural folding results in a superposed tangential longitudinal strain expressed by fractures with a high (hydraulic) connectivity in the hinge zones. Strain partitioning is caused by flexural interlayer slip along incompetent schist layers in the fold limbs. Bed-parallel slip localization zones probably have low porosity and permeability and may act as barriers to fluid migration across beds. We suggest that heterogeneous vertical axis rotation, which occurred as the system's hanging wall slid over the footwall ramp, increased the complexity of fracture networks within the Sinon Anticline. Our findings indicate that the evolution, connectivity, and fluid flow properties of fracture networks can be characterized through careful interpretation of folding mechanisms and related strain states during for-mation of fault-bend fold systems.

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