Modelling Of Fission Track Data Research Articles

Multi-stage tectonic events of the Eastern Kunlun Mountains, Northern Tibetan Plateau constrained by fission track thermochronology

The present Tibetan plateau is a collage of several terranes, including the Lhasa, Qiangtang, Songpan-Ganzi and Kunlun-Qaidam terranes. Following closure of the Palaeo- and Neo-Tethyan oceans, the terranes of the Tibetan plateau migrated northward, and the deformation timing of the northern part of the Songpan-Ganze terrane between Golmud and Dulan in the Eastern Kunlun Orogenic Belt (EKOB) is still poorly understood. Fission track (FT) analysis of zircon and apatite from two localities between Golmud and Dulan has yielded new information about the timing of deformation in EKOB. Samples collected from Aikeng and Boguole yielded zircon and apatite FT central age ranges of ~193–133 Ma and ~103–29 Ma respectively. Thermal history modelling of FT data revealed five major episodes of cooling in these regions at ~200–170 Ma, ~170–100 Ma, ~100–50 Ma, ~50–18 Ma, and ~18–0 Ma. Stage one represents the collision between the Qiangtang and Kunlun tectonic blocks and the closure of the Songpan-Ganzi-Bayan Har Triassic turbidite basin. In stage two, the northward subduction of the Neo-Tethys oceanic plate accentuated sediment transport to the actively closing ocean basin between the Lhasa and Qiangtang terranes, the far-field effect of collision caused the cooling of the EKOB. Stage three is characterised by tectonic quiescence, which ended at ~50 Ma due to the collision of India and Asia. In stage four, the establishment of a strike-slip fault system and fold-thrust belt in the EKOB resulted in exhumation. Stage five saw rapid cooling in response to the most recent compressional event associated with fault development in the EKOB.

Uplift age and rates of the Gurvan Bogd system (Gobi-Altay) by apatite fission track analysis

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.