| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | July 18, 2017 |
| Latest Amendment Date: | July 29, 2022 |
| Award Number: | 1650162 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Colin A. Shaw
cshaw@nsf.gov (703)292-7944 EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | August 15, 2017 |
| End Date: | July 31, 2023 (Estimated) |
| Total Intended Award Amount: | $245,452.00 |
| Total Awarded Amount to Date: | $245,452.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
438 WHITNEY RD EXTENSION UNIT 1133 STORRS CT US 06269-9018 (860)486-3622 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
215 Glenbrook Rd., Unit 4148 Storrs CT US 06269-4148 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | Tectonics |
| Primary Program Source: |
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| Program Reference Code(s): | |
| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
Taiwan represents one of the most active tectonic environments on Earth. The island marks the collision between the Luzon volcanic arc and the passive margin of Asia and for decades the collision has motivated geodynamic models to explain the evolution of many mountain belts around the world. This collision drives deformation and active uplift of the Taiwan mountain belt. Because of the very rapid uplift and high erosion rates the metamorphic core of Taiwan is exposed in the core of Taiwan's Central Range and its eastern margin. Here, a joint team of U.S. and Taiwanese scientists and students is exploring the idea that exhumation of the metamorphic rocks is facilitated by extension rather than the collision-driven shortening model that is usually invoked. The researchers will examine the geometry of the metamorphic rocks and the movement patterns of active faults to determine the mechanisms by which the rocks are exhumed. In addition to providing new insights into mountain building processes, the project advances desired societal outcomes through participation of women and underrepresented minorities in STEM; (b) development of a diverse, globally competitive STEM workforce through undergraduate and graduate student training plus a workshop for Taiwan undergraduate students; and (c) increased partnerships through international collaboration.
More specifically, the objective of this project is to document the plastic-to-brittle exhumation history of the metamorphic core of Taiwan. The metamorphic core (the Tananao schist) in the eastern Central Range is marked by characteristics that are difficult to explain in the context of a steady-state, doubly-vergent orogenic wedge; the current prevailing model. In most parts of the mountain belt, metamorphic foliations are steeply dipping, forming a regional cleavage fan that is east dipping in the west and west dipping in the east. Close to the collisional suture (Longitudinal Valley) this simple pattern breaks down and the youngest metamorphic foliation is commonly gently dipping. Moreover, most mesoscale faults observed to date in this area record normal displacement and accommodate NE-SW extension, the same extension direction as recorded in crustal earthquakes. The researchers aim to test the hypothesis that normal displacement faults and shear zones accommodate syn-collision exhumation of the metamorphic core in eastern Taiwan. This will entail systematically documenting the geometry and kinematics of the youngest metamorphic fabrics and overprinting brittle structures in the Tananao Schist, and establishing the relation between the plastic-to-brittle deformation patterns and ongoing deformation as constrained by seismotectonics and seismic tomography. The research team composed U.S. and Taiwanese scientists and graduate and undergraduate students will collect metamorphic fabric data, and oriented rock samples for petrographic and XCT analyses. Kinematic data for ductile shear zones and overprinting brittle structures, e.g., faults and joints, will also be collected. The existing catalog of earthquake focal mechanisms will be supplemented with new mechanisms generated from Taiwan Central Weather Bureau data. The results will be integrated with seismic tomography and seismotectonic constraints on active deformation to better understand the mechanisms behind exhumation of Taiwan?s metamorphic core.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Intellectual Merit
Reconstructing an active mountain belt: From strike-slip and extrusion of high-pressure rocks to the birth of modern Taiwan
Recent publications on the geologic and structural histories of the Taiwan orogen suggest a tectonic regime dominated by highly oblique plate convergence from ~6 Ma to ~1.0 Ma. This tectonic setting contrasts markedly with the nearly orthogonal convergence observed today, suggesting a recent transition in tectonic regimes.
As a result of our research, we propose a three-stage deformation history of the Taiwan mountain belt that reconstructs the belt 6 Ma to 1,0 Ma (Fig. 1; from Byrne et al., 2024). The first stage involves oblique plate convergence partitioned into plate-boundary perpendicular and plate-boundary parallel components as recorded in the deformation histories of the Slate and Tailuko Belts, respectively (Ho et al., 2022). The metamorphic core, where we focused, records the plate-boundary parallel deformation as strike-slip deformation in the Tailuko Belt, D2 in Fig. 1. The second stage is marked by the partial subduction of Eurasian continental crust, which partly drove tectonic exhumation and nearly vertical extrusion of previously subducted materials, including rocks that record paleo-pressures up to 2.0 GPa, Yuli Belt and D3 in Fig. 1. The third stage is marked by the westward motion of the extruding rocks, which offset the pre-existing strike-slip fault, forming a left-stepping extensional bend, see D4 in Fig. 1. This offset zone filled with the extruding Yuli Belt as the upper crust was structurally thinned. Crustal thinning during this third stage may also have limited surface uplift, consistent with studies showing low topographic relief from ca 3.0 Ma to 1.0 Ma (Chang et al., 2023).
Finally, the transition from the third deformation stage to nearly orthogonal plate convergence observed today is marked by the cessation of tectonic exhumation in the metamorphic core of the Backbone Range at 0.7 Ma, the formation of orogenic oroclines in the northern and southern parts of the range. This final change in tectonics is consistent with the change in motion of the Philippine Sea Plate relative to Eurasia. For example, in southwest Japan, where the plate boundary trends more easterly, geological and geophysical studies suggest a change in kinematic regimes from nearly orthogonal plate convergence to RL oblique convergence <1.0 Ma. The change in kinematics is opposite to the change observed in Taiwan because the orientations of the plate boundaries differed by ~70°.
References
Byrne, T., Chojnacki, M., Lewis, J., Lee, J.-C., Ho, G.-R., Yeh, E.-C., Lee, Y.-H., Tsai, C.-H., Evans, M., and Webb, L., 2024, Tectonic exhumation of a metamorphic core in an arc-continent collision during oblique convergence, Taiwan: Progress in Earth and Planetary Science, v. 11, no. 1, p. 23.
Chang, Q., Hren, M., Lai, L. S.-H., Dorsey, R., and Byrne, T., 2023, Rapid topographic growth of the Taiwan orogen since 1.5 Ma: Science Advances, v. 9.
Ho, G.-R., Byrne, T. B., Lee, J.-C., Mesalles, L., Lin, C.-W., Lo, W., and Chang, C.-P., 2022, A new interpretation of the metamorphic core in the Taiwan orogen: A regional-scale, left-lateral shear zone that accommodated highly oblique plate convergence in the Plio-Pleistocene: Tectonophysics, v. 833, p. 229332.
Broader Impacts
Graduate and Higher Education
MS thesis by Michael Chojnacki, 2019
Title: Late-stage deformation and exhumation of a high-pressure metamorphic belt in an active, arc-continent collision, Taiwan
The PI was also a co-advisor for a PhD student at National Taiwan University, Wei-Hao Hsu (PhD, 2023), and a Post-Doc at the Institute of Earth Sciences, Academia Sinica, Taipei, Dr. Gong-Ruei Ho.
Structural Petrology, Taipei, Taiwan
The PIs, Byrne and Dr. Jon Lewis, IUP, and their Taiwan colleagues, Drs. Jian-Cheng Lee and Chin-Ho Tsai organized and taught a 2-day short course on Structural Petrology in 2018 at the University of Science and Technology in Taipei, Taiwan. The short course utilized samples collected from Taiwan and other classic localities worldwide. The instructors provided a suite of rocks and thin sections ranging from slates to mylonites.
The two-day course was run in the petrology laboratory of Prof. Wei Lo at the National Taipei University of Technology. Prof. Lo volunteered his research microscope and borrowed an additional 9 petrographic microscopes for the course. He also made available to the group a microscope camera and a large screen projecting system for sharing observations with the entire class. The two days of petrographic observations and discussions were followed by a two-day field trip to Taroko Gorge.
Study-Abroad: Geohazards in Taiwan for two weeks in 2017, 2019, and 2023.
The study-abroad courses in Taiwan focused on geohazards (earthquakes, landslides, and tropical storms) and included primarily undergraduate students from the US and Taiwan. The courses were coordinated with the National Taiwan University, National Chung Kung University, and National Taiwan Normal University faculty. The program was significantly enriched with up-to-date research results and a modern understanding of orogenic processes.
Last Modified: 05/25/2024
Modified by: Timothy B Byrne
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