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| Titel |
Westernmost Tian Shan (Uzbekistan): Magmatism and Exhumation |
| VerfasserIn |
Sanaa Abdulhameed, Lothar Ratchbacher, Lukasz Gagala, Raymond Jonkheere |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250098489
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| Publikation (Nr.) |
 EGU/EGU2014-14169.pdf |
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| Zusammenfassung |
| The westernmost segment of the Tian Shan comprises the Ghissar–Alai Range of Tajikistan
and Uzbekistan; its southwestern promontory contains the Baysunta crystalline
massif. This orocline extends northwest of the Pamir and southeast of the Turan
platform and forms the (north) western margin of the intra-orogenic Afghan-Tajik
basin that was inverted during the India–Asia collision, mainly as a result of the
gravitational collapse of the Pamir Plateau. The area contains Paleozoic slope and
shelf clastics mantling crystalline basement rocks, altogether intruded by massif
granitoids; it hides the cryptic Late Paleozoic South Ghissar suture. In Uzbekistan,
the crystalline basement rocks of the westernmost Tien Shan are involved in the
folding and thrusting of the Jurassic to Neogene sediments of the Afghan–Tajik
basin, spectacularly proving thick-skinned deformation and demonstrating basement
involvement below the Jurassic evaporate décollement underneath the Afghan–Tajik
basin.
We sampled the crystalline basement rocks of the Tian Shan of Uzbekistan to constrain
the formation of the enigmatic Baysunta block and date the crystallization and high-grade
metamorphism of the granitoids and associated metamorphic rocks of the Ghissar range; we
employed U–Pb zircon geochronology. To time the deformation and exhumation of the
fold-and thrust belt of the westernmost Afghan–Tajik basin, we used apatite fission-track
thermochronology.
Concordant U–Pb crystallization ages of zircons in the orthogneiss and paragneiss
comprise 620 to 300 Ma; the Neoproterozoic ages imply a correlation of the Baysunta block
with the Garm crystalline massif of the central Ghissar–Alai range of northeastern Tajikistan.
The youngest zircon crystallization ages from granitoids are ~220 Ma, revealing
enigmatically young magmatism, post-dating the last known collision event by >50 Ma.
Together with 270–240 Ma meta-basaltic dykes and stocks in Tajikistan, they may trace a
regional post-orogenic delamination event.
The apatite fission-track thermochronology suggests a two-phase exhumation history.
Exhumation/cooling within the age range of ~17 and 4 Ma and clustering around 10 Ma date
slip along the thick-skinned thrusts. This demonstrates the impact of the India–Asia
collision on the edge of the Turan platform, far northwest of the western edge of the
collision zone. Ages from the northwestern edge of the study area cover 197 to 69 Ma;
they trace a fossil partial annealing zone. They show that the Tian Shan along the
margin of the Turan platform was never covered by sedimentary rocks >3 km thick. |
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