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Structure and Deformation History of the Rapidly Growing Tainan Anticline at the Deformation Front of the Taiwan Mountain Belt

Abstract : This study aims at further documenting the mechanisms of shortening at the front of fold-and-thrust belts. We focus on an actively growing anticline located at the deformation front of the Taiwan fold-and-thrust belt. Based on a multidisciplinary approach combining mainly subsurface data and geodetic techniques, we show that the Tainan anticline is a pure-shear fault-bend fold growing above a 38-45° west dipping back thrust, the Houchiali fault, rooted on a 3.8-km-deep detachment. The cumulative shortening is estimated at 2-3 km since 310 ± 50 ka, including 30-50% of horizontal compaction shortening. The significance of the fold is little in terms of total shortening at the scale of the mountain piedmont, yet the Holocene shortening rate of 10.3 ± 1.0 mm/a accounts for 25% of the present-day shortening rate across the piedmont. Earthquake scaling relationships applied to the Houchiali fault predict Mw 6 earthquakes that would occur a lot more frequently than indicated from historical earthquake catalogs. Hence, the aseismic slip behavior observed from geodetic measurements since two decades is a representative behavior of the fault at least at the scale of a few centuries. Our results bear out the dominance of pure-shear folding at the front of fold-and-thrust belts and support horizontal compaction as a significant shortening mechanism. In contrast, the back thrust wedge structure and the aseismic slip are peculiar characteristics that likely arise from the combination of low friction and high-pore pressure related to the thick mudstone formation hosting the wedge and of high syntectonic sedimentation rates.
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Submitted on : Wednesday, June 29, 2022 - 7:49:12 AM
Last modification on : Wednesday, June 29, 2022 - 7:49:18 AM
Long-term archiving on: : Monday, October 3, 2022 - 3:45:15 PM

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Maryline Le Béon, Odin Marc, John Suppe, Mong-Han Huang, Shiuh-Tsann Huang, et al.. Structure and Deformation History of the Rapidly Growing Tainan Anticline at the Deformation Front of the Taiwan Mountain Belt. TECTONICS, 2019, 38, pp.3311-3334. ⟨10.1029/2019TC005510⟩. ⟨insu-03707752⟩

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