Testing the effects of topography, geometry, and kinematics on modeled thermochronometer cooling ages in the eastern Bhutan Himalaya
In this study, reconstructions of a balanced geologic cross section in the Himalayan fold–thrust belt of eastern Bhutan are used in flexural–kinematic and thermokinematic models to understand the sensitivity of predicted cooling ages to changes in fault kinematics, geometry, topography, and radio...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-05-01
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| Series: | Solid Earth |
| Online Access: | https://www.solid-earth.net/9/599/2018/se-9-599-2018.pdf |
| Summary: | In this study, reconstructions of a balanced geologic cross section in the
Himalayan fold–thrust belt of eastern Bhutan are used in flexural–kinematic
and thermokinematic models to understand the sensitivity of predicted cooling
ages to changes in fault kinematics, geometry, topography, and radiogenic
heat production. The kinematics for each scenario are created by sequentially
deforming the cross section with ∼ 10 km deformation steps while
applying flexural loading and erosional unloading at each step to develop a
high-resolution evolution of deformation, erosion, and burial over time. By
assigning ages to each increment of displacement, we create a suite of
modeled scenarios that are input into a 2-D thermokinematic model to predict
cooling ages. Comparison of model-predicted cooling ages to published
thermochronometer data reveals that cooling ages are most sensitive to
(1) the location and size of fault ramps, (2) the variable shortening rates
between 68 and 6.4 mm yr<sup>−1</sup>, and (3) the 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
used the observed misfit of predicted to measured cooling ages to revise the
cross section geometry and separate one large ramp previously proposed for
the modern décollement into two smaller ramps. The revised geometry
results in an improved fit to observed ages, particularly young AFT ages
(2–6 Ma) located north of the Main Central Thrust. This study presents a
successful approach for using thermochronometer data to test the viability of
a proposed cross section geometry and kinematics and describes a viable
approach to estimating the first-order topographic evolution of a
compressional orogen. |
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| ISSN: | 1869-9510 1869-9529 |