| Title | Relict topography of the Hangay Mountains in central Mongolia: quantifying long-term exhumation and relief change of an old landscape |
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| Author | McDannell, K T ;
Zeitler, P K; Idleman, B D |
| Source | Tectonics 2018 p. 2531-2558, https://doi.org/10.1029/2017TC004682  Open Access |
| Image |  |
| Year | 2018 |
| Alt Series | Natural Resources Canada, Contribution Series 20180167 |
| Publisher | American Geophysical Union (AGU) |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf; html |
| Area | Hangay Mountains; Selenga River; Orkhon River; Mongolia |
| Lat/Long WENS | 88.5000 112.0000 53.0000 44.0000 |
| Subjects | tectonics; structural geology; geochronology; surficial geology/geomorphology; crustal evolution; tectonic history; erosion; crustal uplift; thermal history; modelling; topography; glaciation; isostasy;
orogenies; glacial landforms; cirques; glacial deposits; moraines; climate; bedrock geology; structural features; fault zones; radiometric dating; apatite; erosion rates; thermal analyses; kinematic analysis; paleotopography; Mongolian Plateau;
Mongol-Okhotsk Orogeny; Last Glacial Maximum; Phanerozoic; Cenozoic; Mesozoic; Cretaceous; Jurassic |
| Illustrations | location maps; geoscientific sketch maps; photographs; satellite images; block diagrams; graphs; schematic diagrams; tables; histograms; plots; models |
| Program | GEM2: Geo-mapping for Energy and Minerals GEM Synthesis |
| Released | 2018 08 12 |
| 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 (2-sigma). 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. |
| Summary | (Plain Language Summary, not published)
The Hangay Mountains in central Mongolia are a mysterious area of high topography within central Asia. The region is at elevations over 4000 meters, yet
has low relative topographic relief, or a lack of dramatic mountain peaks regionally. A variety of mechanisms have been proposed as to why this area is at high elevations. The high-elevation topography of the Hangay has typically been thought of as a
more youthful feature, uplifted and created in the last 20-30 million years, however, the geochemical and geologic data presented here suggest this is a very old mountain landscape that has persisted for over 100 million years. Numerical modeling
performed for central Mongolia advocates for a scenario where higher topographic relief existed in the Mesozoic, was rapidly eroded, and over the past ca. 100 million years has undergone very minimal erosion due to a persistently arid climate and
very little plate tectonic activity. |
| GEOSCAN ID | 308485 |
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