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Solid Earth An interactive open-access journal of the European Geosciences Union

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https://doi.org/10.5194/se-2017-117
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
26 Oct 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Solid Earth (SE).
Testing the effects of topography, geometry and kinematics on modeled thermochronometer cooling ages in the eastern Bhutan Himalaya
Michelle E. Gilmore1, Nadine McQuarrie1, Paul Eizenhöfer1, and Todd A. Ehlers2 1Department of Geology and Environmental Science, University of Pittsburgh, Pittsburgh, 15260, USA
2Department of Geoscience, University of Tübingen, Tübingen , D-72074 , Germany
Abstract. The temporal and kinematic evolution of fold-thrust belts is a critical component for evaluating the viability of proposed plate tectonic, geodynamic and even climatic processes in regions of convergence. Thermochronometer data have the potential to provide temporal constraints, but interpretations of these data are sensitive to both exhumational and deformational processes. In this study, reconstructions of a balanced geologic cross section in the Himalayan fold-thrust belt of eastern Bhutan are used in a flexural and thermal-kinematic model to understand the sensitivity of predicted cooling ages to changes in fault kinematics, geometry and topography. We sequentially deform the cross section with ~ 10 km deformation steps and apply flexural loading and erosional unloading at each step to develop a high-resolution evolution of deformation, erosion, and burial over time. Comparison of model-predicted cooling ages to published thermochronometer data reveals that cooling ages are most sensitive to (1) location and magnitude of fault ramps, (2) variable shortening rates between 68-6.4 mm/yr, and (3) timing and magnitude of out-of-sequence faulting. The predicted ages are less sensitive to (4) radiogenic heat production, and (5) estimates of topographic evolution. We propose a revised cross section geometry that separates one large ramp previously proposed for the modern decollement into two smaller ramps. The revised cross section results in an improved fit to observed ages, particularly young AFT ages (2–6 Ma) located north of the Main Central Thrust.

Citation: Gilmore, M. E., McQuarrie, N., Eizenhöfer, P., and Ehlers, T. A.: Testing the effects of topography, geometry and kinematics on modeled thermochronometer cooling ages in the eastern Bhutan Himalaya, Solid Earth Discuss., https://doi.org/10.5194/se-2017-117, in review, 2017.
Michelle E. Gilmore et al.
Michelle E. Gilmore et al.
Michelle E. Gilmore et al.

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Short summary
We examine the Himalayan Mountains of Bhutan by integrating balanced geologic cross sections with cooling ages from a suite of mineral systems. Interpretations of cooling ages are intrinsically linked to both the motion along faults as well as the location and magnitude of erosion. In this study, we use flexural and thermal-kinematic models to understand the sensitivity of predicted cooling ages to changes in fault kinematics, geometry and topography.
We examine the Himalayan Mountains of Bhutan by integrating balanced geologic cross sections...
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