Gilmore, Michelle E.
(2014)
QUANTIFYING DEFORMATION IN THE EASTERN BHUTAN HIMALAYA:
INSIGHTS FROM FLEXURAL AND THERMAL-KINEMATIC MODELS OF A
BALANCED CROSS SECTION.
Master's Thesis, University of Pittsburgh.
(Unpublished)
Abstract
Reconstructions of a balanced geologic cross section in the Himalayan fold-thrust belt of eastern Bhutan are used in a thermal-kinematic model to understand the first order controls on thermochronometer cooling ages and track magnitude, timing and rates of deformation. We model the cross section with sequential ~10-km deformation steps and apply flexural loading and
erosional offloading at each step to develop a high-resolution evolution of deformation, topography and foreland basin development in the fold-thrust belt over time. Models of topography combined with varied timing of out-of-sequence motion along the Kakhtang Thrust affect the intermediate deformational and exhumational history. We use these flexural models coupled with varying heat production values and velocities of deformation as input in the
thermal-kinematic model Pecube to forward model apatite fission track (AFT), zircon (U-Th/He) (ZHe), and muscovite 40Ar/39Ar (MAr) cooling ages during fold-thrust belt development. Comparing the predicted ages to published cooling ages along the section reveals that cooling ages are sensitive to (1) variable shortening rates, (2) how modeled topography accommodates structural uplift and flexural loading, (3) kinematic timing of fault motion, and (4) cross section geometry. Models maintaining a temporally constant deformation rate do not adequately predict cooling ages that match existing AFT, ZHe, and MAr data. Better fits to data are generated in models that use published estimates of temporally variable shortening rates. Best fits to the suite of published cooling ages required motion along the Kakhtang Thrust both before and after
duplexing of Upper Lesser Himalayan rocks, topography that can dynamically account for structural uplift and flexural loading, heat production value of 2.5 μW/m3, and variable deformation rates ranging from 74 mm/a to 4 mm/a. Young AFT ages (2-6 Ma) observed north of the Main Central Thrust cannot be matched in the best fitting models. We attribute this misfit to (1) a partitioning of shortening along the Kakhtang Thrust that is both kinematically and flexurally different than the models presented in this study, and/or (2) the geometry of the cross section, which may require a modified decollement north of the surface exposure of the Shumar Thrust.
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Details
| Item Type: |
University of Pittsburgh ETD
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| Status: |
Unpublished |
| Creators/Authors: |
| Creators | Email | Pitt Username | ORCID  |
|---|
| Gilmore, Michelle E. | | | |
|
| ETD Committee: |
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| Date: |
9 September 2014 |
| Date Type: |
Publication |
| Defense Date: |
8 August 2014 |
| Approval Date: |
9 September 2014 |
| Submission Date: |
15 August 2014 |
| Access Restriction: |
5 year -- Restrict access to University of Pittsburgh for a period of 5 years. |
| Number of Pages: |
71 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Dietrich School of Arts and Sciences > Geology and Planetary Science |
| Degree: |
MS - Master of Science |
| Thesis Type: |
Master's Thesis |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
n/a |
| Date Deposited: |
09 Sep 2014 22:03 |
| Last Modified: |
09 Sep 2019 05:15 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/22751 |
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