1 Relict topography within the Hangay Mountains in central Mongolia: 2 Quantifying long-term exhumation and relief change in an old landscape 3 4 Kalin T. McDannella,b*, Peter K. Zeitlera, and Bruce D. Idlemana 5 6 aDepartment of Earth & Environmental Sciences, Lehigh University, 1 W Packer Ave., Bethlehem, PA 18015, USA 7 8 bNatural Resources Canada, Geological Survey of Canada, 3303 33 St NW, Calgary, AB T2L 2A7 9 10 Corresponding author:
[email protected] 11 12 Key Points 13 ° New bedrock and detrital apatite (U-Th)/He cooling ages were determined for the Hangay 14 Mountains and central Mongolia 15 ° Thermo-kinematic modeling suggests relief change in the Mesozoic with slow exhumation 16 rates on the order of <20 m/My since the Cretaceous 17 ° Coupled Pecube-Neighborhood Algorithm modeling is successfully applied in a slowly 18 eroding setting 19 20 Abstract 21 The Hangay Mountains are a high-elevation, low-relief landscape within the greater Mongolian 22 Plateau of central Asia. New bedrock apatite (U-Th)/He single-grain ages from the Hangay span 23 ~70 to 200 Ma, with a mean of 122.7 ± 24.0 Ma (2σ). Detrital apatite samples from the Selenga 24 and Orkhon Rivers, north of the mountains, yield dominant (U-Th)/He age populations of ~115 25 to 130 Ma, as well as an older population not seen in the Hangay granitic bedrock data. These 26 low-temperature data record regional exhumation of central Mongolia in the Mesozoic followed 27 by limited erosion of <1-2 km since the Cretaceous, ruling out rapid exhumation of this 28 magnitude associated with any late Cenozoic uplift.