Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The dating of the uplift onset of the Mongolian mountain ranges, the northernmost relief associated with the India-Eurasia convergence, is a fundamental issue to better understand the mechanisms of propagation of the Cenozoic transpressive deformation in Central Asia. Using apatite fission tracks we determined the timing and strain rates of the tectonics affecting the Gurvan Bogd system, in the Gobi-Altay, since the Middle Mesozoic to the Late Cenozoic. The region was firstly affected by a Lower-Middle Jurassic tectonic phase, characterized by a vertical crustal movement larger than 2 km. Then followed a protracted period without major crustal vertical movements until the last uplift phase. The peneplanation of the Jurassic relief produced an erosional surface that has undergone negligible denudation or sedimentation for more than 100 Ma. This same surface corresponds to the present summit plateaux of the massifs, standing about 2000 m above the surrounding region, which corresponds to the vertical movement produced by the ongoing uplift. Modelling of fission track data from the massifs of Ih Bogd and Baga Bogd shows that this uplift phase probably started at 5 ± 3 Ma. The Gobi-Altay mountain range appears therefore as one of the youngest mountain ranges in Central Asia, which is consistent with the idea of a northward propagation of the transpressional deformation from the Himalayan front to the Siberian craton. The Cenozoic uplift rate of the massifs is estimated to be between 0.25 and 1 mm/yr, which is slightly higher than the upper Pleistocene vertical slip rates of the bordering faults. This suggests that thrust faults observed within the massifs would increase the uplift rate inside the massifs compared to the uplift rate determined at their boundaries.
ISSN: 0012-821X

insu-00191116
https://hal-insu.archives-ouvertes.fr/insu-00191116
DOI : 10.1016/j.epsl.2007.04.047

Éditeur(s) : HAL CCSD
Résumé : International audience
The history of the peneplain in East Sayan was studied using apatite fission-track analysis (AFTA). This method is suitable for determining the formation time of the erosional surface and estimating its denudation rate. The largest known relic of the peneplanation surface in this area is the Oka Plateau, separated from the Kropotkin Ridge by the Oka-Jombolok fault. The AFTA shows that the peneplain on the Oka Plateau formed in the Late Jurassic-Early Cretaceous. This peneplain is much younger than the erosional surfaces that persist today in the Tien Shan, Gobi Altai, and Mongolian Altai (Early Jurassic). However, it is older than the peneplain on the Chulyshman Plateau, Altai (Late Cretaceous), suggesting asynchronous formation of the ancient peneplain in Central Asia. The similar exhumation histories of samples from the Oka Plateau and Kropotkin Ridge indicate that these morphotectonic structures developed from Jurassic to late Miocene as a single block, which underwent continuous slow denudation at an average rate of 0.0175 mm/yr. Active tectonic processes in the Late Miocene caused the destruction of the peneplanation surface and its partial uplifting to different altitudes. The rate of Pliocene-Quaternary vertical movements along the Oka-Jombolok fault is roughly estimated at 0.046-0.080 mm/yr, which is several times higher than the denudation rate in this area. During the Pliocene-Quaternary, the Oka Plateau has not undergone any significant morphologic changes owing to its intermediate position between the summit plain and datum surface of East Sayan and to its partial shielding by basaltic lavas.
Russian Geology and Geophysics

insu-00839215
https://hal-insu.archives-ouvertes.fr/insu-00839215
DOI : 10.1016/j.rgg.2013.06.004