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We studied the patterns, rates and evolution of fluvial terraces and fault system during the building process of an intracontinental transpressional mountain in the Gobi-Altay (Mongolia). By analyzing incisions and offsets of fluvial terraces and alluvial fans, we show that the massif has grown by outward migration of thrust faults through time. On the northern flank, the present bounding thrust fault began its activity ∼600 ka ago, while a more internal sub-parallel fault was still active until ∼200-100 ka. Vertical offset of an alluvial fan abandoned ∼100 ka ago allows an estimate of 0.1 mm/yr Upper Pleistocene - Holocene uplift rate. The morphology of the catchment-piedmont system strongly suggests a periodical formation of the alluvial surfaces, controlled by the climatic pulses, at the beginning of the wet interglacial periods. The abandonment of the alluvial terraces lags by several thousand years the abandonment of the alluvial fans, showing a diachronous incision propagating upstream. The incision rate deduced from the different elevations of straths exceeds of one order of magnitude the rock uplift rate. This excess is mostly due to ongoing drainage network growth at the core of the massif, and incision due to alluvial apron entrenchment near the outlet. This implies that fluvial response is mainly controlled by drainage growth, interaction with piedmont and cyclic climatic variations, rather than by rock uplift. [ABSTRACT FROM AUTHOR]

Abstract: In an attempt to date a palaeolandslide that took place along the Baga Bogd Massif, in Mongolia, the infrared stimulated luminescence (IRSL) method has been applied to lacustrine silty sediments directly overlying the landslide mass. The IRSL age estimates obtained on alkali feldspar grains (>40μm) and polymineral fine grains (4–11μm) provide a minimum age for the landslide event. The IRSL ages on alkali feldspars corrected for long-term fading using the protocol of Mejdahl (1988, 1989) suggest that the palaeolandslide occurred at the beginning of the Last Interglacial. These are in good agreement with the 10Be cosmogenic dates obtained on faulted and abandoned alluvial fans in the Gobi-Altay mountains. This study demonstrates for the first time that the IRSL dating method can successfully be applied for establishing landslide chronologies. [Copyright &y& Elsevier]

Most mid-latitude mountain glaciers reached their maximum extent around the global Last Glacial Maximum (gLGM). However, some also strongly responded to the regional climate change or local non-climatic factors such as topography, leading to asynchronous maximum advances. This study documents the maximum extent and chronology of two paleoglaciers in the Ih Bogd massif of Mongolia: one facing north into the Jargalant Valley and the other facing south into the Ih Artsan valley. 10Be surface exposure age dating revealed that the Ih Artsan short valley glacier reached its maximum position (MIh1) around 20.1 ± 0.7 ka, coinciding with the gLGM. In contrast, the Jargalant paleoglacier (MJ1) reached its maximum extent around 17.2 ± 1.5 ka, around Heinrich 1 stadial and during the post-gLGM northern hemisphere warming. Our 2D ice surface model, which includes the temperature-index melt model, suggests that an aspect can result in a melt difference between north and south-facing slopes. Glaciers retreated from their maximum modeled extent asynchronously when we assign a 0.5° lower temperature for Jargalant valley (northern slope), based on the observation that present-day mean annual Jargalant temperatures are lower than in the south-facing Ih Arstan. Modelled timing of the maximum extents (20.23 ka in Ih Artsan, 17.13 ka in Jargalant) are consistent with 10Be exposure age results (20.1 ka in Ih Artsan, 17.2 ka in Jargalant). We also observed several sequences of post LGM or/and Holocene moraines in both cirques. Extremely old ages ranging from 636.2 ka to 35.9 ka were measured for the inner moraines in the Jargalant cirque (MJ2-MJ4), suggesting a problem with inheritance from boulders eroded from the summit plateau. [ABSTRACT FROM AUTHOR]

Abstract: The Hangay Mountains are a high‐elevation, low‐relief landscape within the greater Mongolian Plateau of central Asia. New bedrock apatite (U‐Th)/He single‐grain ages from the Hangay span ~70 to 200 Ma, with a mean of 122.7 ± 24.0 Ma (2σ). Detrital apatite samples from the Selenga and Orkhon Rivers, north of the mountains, yield dominant (U‐Th)/He age populations of ~115 to 130 Ma, as well as an older population not seen in the Hangay granitic bedrock data. These low‐temperature data record regional exhumation of central Mongolia in the Mesozoic followed by limited erosion of <1–2 km since the Cretaceous, ruling out rapid exhumation of this magnitude associated with any late Cenozoic uplift. Apatite (U‐Th)/He age elevation patterns suggest long‐term thermal stability of the upper crust and thermal model inversions require late Mesozoic uplift, spatially variable exhumation, and/or relief evolution to produce the observed cooling ages in the Hangay. Regionally, modeling suggests reduction of topography in the Jurassic followed by relief growth that was completed by the mid‐Cretaceous. These results support Mesozoic topographic evolution and relative stability of the landscape throughout the Cenozoic with very little subsequent exhumation. Alpine cirques and intact moraines are indicative of more recent, modest climate‐driven erosion in the higher peaks of the western Hangay. These data reinforce the notion that in the absence of strong tectonic or climate forcing, erosion is limited and remnant landscapes can persist over tens to hundreds of millions of years in a state of disequilibrium. [ABSTRACT FROM AUTHOR]

Single zircon ages determined by ion microprobe (SHRIMP II) for granitoid gneisses from the southern slope of the Baga Bogd massif (Gobi-Altai, southern Mongolia) reveal several episodes of zircon growth, ranging from late Palaeoproterozoic to late Cambrian. The oldest events are documented by a zircon crystallization age for a gneiss protolith at 1519 ± 11 Ma and by a xenocrystic zircon from a dark grey augen-gneiss yielding an age of c. 1701 Ma. Discrete igneous events are recorded in granite-gneisses with protolith emplacement ages of 983 ± 6, 956 ± 3 and 954 ± 8 Ma. These ages provide the first record of early Neoproterozoic magmatic activity in this region. A much younger and discrete magmatic event is recorded by several dioritic to granitic orthogneisses which are tectonically interlayered with the older gneisses and have protolith emplacement ages between 502 and 498 Ma. These late Cambrian granitoids of calc-alkaline affinity are likely to have been emplaced along an active continental margin and suggest that the Baga Bogd Precambrian crustal fragment was either docked against the southward (present-day coordinates) growing margin of the CAOB or was a large enough crustal entity to develop an arc along its margin. We speculate that the Precambrian gneisses of this massif may be part of a crustal fragment rifted off the Tarim Craton. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Our study is aimed at reconstructing the Palaeozoic–early Mesozoic plate tectonic development of the Central Asian Orogenic Belt in central and southeast Mongolia (Gobi). We use sandstone provenance signatures including laser ablation U-Pb ages of detrital zircons, their epsilon hafnium isotope signatures, and detrital framework grain analyses. We adopt a well-established terran subdivision of central and southeastern Mongolia. However, according to their affinity and tectonic assemblage we group them into three larger units consisting of continental basement, rift-passive continental margin and arc elements, respectively. These are in today's coordinates: (i) in the north the late Cambrian collage from which the later Mongol-Okhotsk and the Central Mongolia-Erguna mountain ranges resulted, (ii) in the south a heterogeneous block from which the South Mongolia-Xin'gan and Inner Mongolia-Xilin belts developed, and (iii) in between we still distinguish the intra-oceanic volcanic arc of the Gurvansayhan terrane. We present a model for paleotectonic development for the period from Cambrian to Jurassic, which also integrates findings from the Central Asian Orogenic Belt in China and Russia. This mobilistic model implies an interplay of rift and drift processes, ocean formation, oceanic subduction, basin inversion, collision and suture formation in space and time. The final assemblage of the Central Asian Orogenic Belt occurred in Early Jurassic. [ABSTRACT FROM AUTHOR]