Dating the incision of the Yangtze River gorge at the First Bend using three‐nuclide burial ages

• Published in: Geophysical research letters 2016-01, Vol.43 (1), p.101-110
• Main Authors: McPhillips, Devin, Hoke, Gregory D., Liu‐Zeng, Jing, Bierman, Paul R., Rood, Dylan H., Niedermann, Samuel
• Format: Article
• Language: English
• Subjects: Accounting; Age; Beryllium 10; burial dating; Caves; Chronology; cosmogenic nuclide; Dating; Duration; Freshwater; Miocene; Mountains; Nuclides; Plateaus; Ratios; river incision; Rivers; Sediment; Sediments; Tibetan Plateau; Time measurement; Uplift; Walls; Yangtze River
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2015GL066780

Incision of the Yangtze River gorge is widely interpreted as evidence for lower crustal flow beneath the southeast margin of the Tibetan Plateau. Previous work focused on the onset of incision, but the duration of incision remains unknown. Here we present cosmogenic nuclide burial ages of sediments collected from caves on the walls of the gorge that show the gorge was incised ~1 km sometime between 18 and 9 Ma. Thereafter, incision slowed substantially. We resolve middle Miocene burial ages by using three nuclides and accounting for in situ muogenic production. This approach explains the absolute concentrations of 10Be, 26Al, and 21Ne, as well as 26Al/10Be and 21Ne/10Be ratios. A declining incision rate challenges existing geodynamic interpretations by suggesting that either (1) surface uplift has ceased immediately south of the plateau margin or (2) gorge incision is not a useful proxy for the timing of surface uplift. Key Points Cosmogenic nuclides 10Be, 26Al, and 21Ne reveal sediment burial ages Burial ages indicate an average gorge incision rate of 0.1 to 0.3 km/Myr between 18 and 9 Ma Incision slowed by about an order of magnitude after 9 Ma