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| Titel |
Formation of the giant Shakhdara migmatitic gneiss dome, Pamir, India-Asia collision zone |
| VerfasserIn |
Konstanze Stübner, Lothar Ratschbacher, Bradley Hacker, István Dunkl, Richard Gloaguen |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250078337
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| Zusammenfassung |
| Cenozoic gneiss domes comprise one third of the surface exposure of the Pamir
Mountains and provide a window into deep crustal processes of the India–Asia collision.
The largest of these is the 350 Ã 90 km Shakhdara–Alichur composite dome of the
southern Pamir, Tajikistan and Afghanistan. The Shakhdara and Alichur domes formed
by footwall exhumation of two low-angle detachments: In the larger Shakhdara
dome the top-to-S South Pamir shear zone (SPSZ) exhumed crust from 30–40 km
depth; in the Alichur dome the top-to-N Alichur shear zone exhumed upper crustal
rocks. The subdomes are separated by a low-strain horst. Non-coaxial shear in the
Shakhdara dome is pervasive over the ~4 km thick SPSZ. The top of the shear
zone is preserved at mountain peaks, the base is incised by the Panj gorge, which
exposes the ‘core’ of the dome; total erosion is less than 4 km throughout most of the
dome.
We use a comprehensive geo-thermochronologic dataset of titanite, monazite, and
zircon U/Th–Pb, mica Rb–Sr and 40Ar/39Ar, zircon and apatite fission track, and
zircon (U-Th)/He ages to constrain the exhumation history of the southern Pamir
domes. Doming started at ~21 Ma by crustal buckling and activation of a top-to-N
normal shear zone (Gunt shear zone) along the northern rim of the Shakhdara dome,
resulting in exhumation and cooling. The bulk of the exhumation was accomplished
by northward extrusion of the SPSZ footwall, which was active from ~18–15 Ma
to ~2 Ma; exhumation rates were 1–3 mm/yr. Erosion rates during and after the
end of doming were 0.3–0.5 mm/yr within the domes and 0.1–0.3 mm/yr in the
horst and in the SE Pamir plateau; incision rates of the major drainages were up to
1.0 mm/yr.
Doming by footwall exhumation of the SPSZ resulted in up to 90 km N–S extension,
coeval with ongoing N–S convergence between India and Asia. Extension opposes shortening
along and above the reactivated Rushan–Pshart suture zone, a wide fold-thrust belt north of
the Shakhdara–Alichur domes. This geometry defines a ‘vertical extrusion’ scenario,
comprising basal top-to-N underthrusting and thickening and hanging gravitationally driven
top-to-S normal shear. |
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