Age of Thrust Development in the Northern and Central Western Foothills of Taiwan: Insight from Apatite Fission Track.
Abstract
This contribution attempts to constraint the timing of thrust activity in the central and northern Western Foothills (WFH) of the active Taiwan mountain belt. The central WFH presently accommodates about one third of the shortening occurring at the collisional plate boundary but the timing of thrust development and frontal propagation and/or out-of-sequence fault activity is poorly known, even if this geological province was critical in the development of the Critical Wedge theory of orogenic development almost 40yrs ago. Recent contributions argue for the existence of out-of-sequence thrusting but very little timing constraints exist. In this study we present over 50 new apatite fission track (AFT) ages mostly from pre-orogenic Miocene sediments samples of the northern and central WFH, as well as from the northern and western flank of the adjacent Hsuehshan Range. The oldest orogenic AFT ages in the northern sector (east of the Taipei basin) are ca.7Ma and consistently become younger towards the frontal thrust where ages reach ca.3Ma, a sequence consistent with frontal thrust propagation. In the central sector (east of the Hsinchu - Miaoli area) we obtain almost undistinguishable AFT ages from the east (Hsuehshan Range) towards the outer western belt, clustering at ca. 1.5Ma. Nevertheless detailed closely spaced transects across fault-propagation-folds in the outer WFH present AFT ages of ca.3Ma in the anticlinal cores while the shallower stratigraphic levels remain unreset. We interpret this pattern as related to deep seated ramps and detachments active in the outer WFH at that time. The younger AFT ages observed in the inner WFH and Hsuehshan Range is interpreted as reflecting out-of-sequence thrusting at ca.1.5Ma, consistent with thermochronological vertical profiles in the area indicating an accelerated exhumation pulse at that time.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T14C..07M
- Keywords:
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- 5475 Tectonics;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS;
- 8102 Continental contractional orogenic belts and inversion tectonics;
- TECTONOPHYSICS;
- 8108 Continental tectonics: compressional;
- TECTONOPHYSICS;
- 8118 Dynamics and mechanics of faulting;
- TECTONOPHYSICS