Exhumation, crustal deformation, and thermal structure of the Nepal Himalaya derived from the inversion of thermochronological and thermobarometric data and modeling of the topography

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Version: author
Serval ID
serval:BIB_AA9E48A3B928
Type
Article: article from journal or magazin.
Collection
Publications
Title
Exhumation, crustal deformation, and thermal structure of the Nepal Himalaya derived from the inversion of thermochronological and thermobarometric data and modeling of the topography
Journal
Journal of Geophysical Research - Solid Earth
Author(s)
Herman F., Copeland P., Avouac J.P., Bollinger L., Maheo G., Le Fort P., Rai S., Foster D., Pecher A., Stuewe K., Henry P.
ISSN-L
0148-0227
Publication state
Published
Issued date
2010
Peer-reviewed
Oui
Volume
115
Pages
B06407
Language
english
Abstract
Two end-member kinematic models of crustal shortening across the
Himalaya are currently debated: one assumes localized thrusting along a
single major thrust fault, the Main Himalayan Thrust (MHT) with
nonuniform underplating due to duplexing, and the other advocates for
out-of-sequence (OOS) thrusting in addition to thrusting along the MHT
and underplating. We assess these two models based on the modeling of
thermochronological, thermometric, and thermobarometric data from the
central Nepal Himalaya. We complement a data set compiled from the
literature with 114 (40)Ar/(39)Ar, 10 apatite fission track, and 5
zircon (U-Th)/He thermochronological data. The data are predicted using
a thermokinematic model (PECUBE), and the model parameters are
constrained using an inverse approach based on the Neighborhood
Algorithm. The model parameters include geometric characteristics as
well as overthrusting rates, radiogenic heat production in the High
Himalayan Crystalline (HHC) sequence, the age of initiation of the
duplex or of out-of-sequence thrusting. Both models can provide a
satisfactory fit to the inverted data. However, the model with
out-of-sequence thrusting implies an unrealistic convergence rate >= 30
mm yr(-1). The out-of-sequence thrust model can be adjusted to fit the
convergence rate and the thermochronological data if the Main Central
Thrust zone is assigned a constant geometry and a dip angle of about 30
degrees and a slip rate of <1 mm yr(-1). In the duplex model, the 20 mm
yr(-1) convergence rate is partitioned between an overthrusting rate of
5.8 +/- 1.4 mm yr(-1) and an underthrusting rate of 14.2 +/- 1.8 mm
yr(-1). Modern rock uplift rates are estimated to increase from about
0.9 +/- 0.31 mm yr(-1) in the Lesser Himalaya to 3.0 +/- 0.9 mm yr(-1)
at the front of the high range, 86 +/- 13 km from the Main Frontal
Thrust. The effective friction coefficient is estimated to be 0.07 or
smaller, and the radiogenic heat production of HHC units is estimated to
be 2.2 +/- 0.1 mu W m(-3). The midcrustal duplex initiated at 9.8 +/-
1.7 Ma, leading to an increase of uplift rate at front of the High
Himalaya from 0.9 +/- 0.31 to 3.05 +/- 0.9 mm yr(-1). We also run 3-D
models by coupling PECUBE with a landscape evolution model (CASCADE).
This modeling shows that the effect of the evolving topography can
explain a fraction of the scatter observed in the data but not all of
it, suggesting that lateral variations of the kinematics of crustal
deformation and exhumation are likely. It has been argued that the steep
physiographic transition at the foot of the Greater Himalayan Sequence
indicates OOS thrusting, but our results demonstrate that the best fit
duplex model derived from the thermochronological and thermobarometric
data reproduces the present morphology of the Nepal Himalaya equally
well.
Open Access
Yes
Create date
07/10/2012 19:46
Last modification date
20/08/2019 15:14
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