Combined uranium series and 10Be cosmogenic exposure dating of surface abandonment: A case study from the Ölgiy strike-slip fault in western Mongolia

L. C. Gregory, A. L. Thomas, R. T. Walker, R. Garland, C. Mac Niocaill, C. R. Fenton, A. Bayasgalan, T. Amgaa, B. Gantulga, S. Xu, C. Schnabel, A. J. West

Research output: Contribution to journalArticlepeer-review

Abstract

Time-averaged fault slip-rates can be established by reliably dating the abandonment of an alluvial deposit that has been displaced by Quaternary movement along a cross-cutting fault. Unfortunately, many Quaternary dating techniques are hindered by uncertainties inherent to individual geochronometers. Such uncertainties can be minimised by combining multiple independent techniques. In this study, we combine <sup>10</sup>Be exposure dating of boulder tops and U-series dating of layered pedogenic carbonate cements accumulated on the underside of clasts from two separate alluvial surfaces. These surfaces are both displaced by the active Ölgiy strike-slip fault in the Mongolian Altay Mountains. We date individual layers of pedogenic carbonate, and for the first time apply a Bayesian statistical analysis to the results to develop a history of carbonate accumulation. Our approach to the U-series dating provides an age of initiation of carbonate cement formation and avoids the problem of averaging contributions from younger layers within the carbonate. The U-series ages make it possible to distinguish <sup>10</sup>Be samples that have anomalously young exposure ages and have hence been subject to the effects of post-depositional erosion or exhumation. The combination of <sup>10</sup>Be and U-series dating methods provides better constrained age estimates than using either method in isolation and allows us to bracket the abandonment ages of the two surfaces as 18.0-28.1kyr and 38.4-76.4kyr. Our ages, combined with measurements of the displacement of the surfaces, yield a right-lateral slip-rate for the Ölgiy fault of 0.3-1.3mmyr<sup>-1</sup>, showing that it is a relatively important structure within the active tectonics of Mongolia and that it constitutes a substantial hazard to local populations.
Original languageEnglish
Pages (from-to)27-43
Number of pages17
JournalQuaternary Geochronology
Volume24
DOIs
Publication statusPublished - 1 Jan 2014

Keywords

  • Active faulting
  • Altay
  • Cosmogenic isotopes
  • Quaternary dating
  • Uranium series

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