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| Titel |
An integrated approach to study the exhumation of rocks in Neelum valley, NW Himalayas, Pakistan. |
| VerfasserIn |
Syed Ali Turab, Kurt Stüwe, Finlay M. Stuart, David M. Chew |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250125234
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| Publikation (Nr.) |
 EGU/EGU2016-4788.pdf |
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| Zusammenfassung |
| Tectonics and erosion have both been suggested as alternative driving mechanisms for rapid
exhumation of rocks in the western Himalayan syntaxis. This debate could be resolved by
understanding the plan view-geometry of the exhumation of rocks in the region: does it
follow the major structures?, or is it related to the drainage geometry? In order to resolve this
geometry we have undertaken a low-temperature thermochronologic study, using
crystalline rocks, of a critical region of the western syntaxis: Neelum valley region,
Pakistan. Apatite (U-Th-Sm)/He (AHe), fission track (AFT) and U-Pb dating has
been combined with geomorphic stream power analysis in order to discern the
relationship of exhumation of rocks to tectonics (main faults) or erosion. Pooled AFT
ages show a range of 2.2 ± 0.4 to 7.0 ± 0.4 Ma (1σ). Recoil corrected AHe ages
exhibit a range from 2.0 ± 0.1 to 8.7 ± 0.5 Ma (1σ). U-Pb ages could be used
to divide the samples in three groups: ages that are completely-, partly- and not-
affected by Himalayan tectonics. The range of apatite U-Pb ages displayed by both
completely- and partly- affected samples is from 17.0 to 43.0 Ma (2σ, unanchored, i.e.
constrained by isochrones alone) and 6.0 to 48.3 Ma (2σ, anchored using the Stacey and
Kramers terrestrial Pb evolution model). Stream power analysis of the Neelum
river catchment indicates a region with high steepness index (Ksn, normalized to
reference concavity, θref = 0.45) values of > 500 m0.9 which coincides well the region
sampled.
In combination with earlier published ages, our data indicate that exhumation contours
run more or less parallel to the major structures in the region. The boundary between samples
with unaffected and affected U-Pb ages as well as transition from high Ksn to lower Ksn
values along the main Neelum river fits well with the mapped trace of the Main Central
Thrust (MCT), corroborating the presence of the MCT in the southeastern parts of our
study area. Thermal history modeling of the AFT and AHe ages indicates recent
rapid exhumation of rocks through the upper 5 - 6 km of the crust. Also, the AFT
ages are younger in proximity to the main faults. This new data supports a model
with tectonics as the main driving mechanism for exhumation of rocks and may
indicate quite recent re-activation of MCT or one of the other major structures near it. |
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