Widespread late Cenozoic increase in erosion rates across the interior of eastern Tibet constrained by detrital low‐temperature thermochronometry

Abstract

[1] New detrital low-temperature thermochronometry provides estimates of long-term erosion rates and the timing of initiation of river incision from across the interior of the Tibetan Plateau. We use the erosion history of this region to evaluate proposed models of orogenic development as well as regional climatic events. Erosion histories of the externally drained portion of the east-central Tibetan Plateau are recorded in modern river sands from major rivers across a transect that spans >750 km and covers a region with no published thermochronometric ages. Individual grains from eight catchments were analyzed for apatite (U-Th)/He and fission track thermochronometry. A wide distribution in ages that, in most cases, spans the entire Cenozoic and Late Mesozoic eras requires a long period of slow or no erosion with a relative increase in erosion rate toward the present. We apply a recently developed methodology for inversion of detrital thermochronometric data for three specified erosion scenarios: constant erosion rate, two-stage erosion history, and three-stage erosion history. Modeling results suggest that rates increase by at least an order of magnitude between 11 and 4 Ma following a period of slow erosion across the studied catchments. Synchroneity in accelerated erosion across the whole of the Tibetan Plateau rather than a spatial or temporal progression challenges the widely held notion that the plateau evolved as a steep, northward-propagating topographic front, or that south to north precipitation gradients exert a primary control on erosion rates. Instead, we suggest that accelerated river incision late in the orogen's history relates to regional-scale uplift that occurred in concert with eastern expansion of the plateau.

Geochronology of the Baye Mn oxide deposit, southern Yunnan Plateau: Implications for the late Miocene to Pleistocene paleoclimatic conditions and topographic evolution

“…The incision rates (235-416 m. Myr -1 ) calculated for the Nanpie River are consistent with the values estimated from zircon and apatite (U-Th)/He and apatite fission-track dating results in the eastern Tibetan Plateau (Kirby et al, 2003;Clark et al, 2005;Ouimet et al, 2010;Duvall et al, 2012). The incision rates are 250-500 m. Myr -1 for the Yalong and Dadu River gorges between 9-13 Ma (Clark et al, 2005), 200-600 m. Myr -1 for the Tsangpo, Salween, Mekong, Yalong, Yellow, and Yangtze River gorges between 4-11 Ma (Duvall et al, 2012), and ca. 330 m. Myr -1 for the Dadu, Yalong, and Yangtze River gorges since about 10 Ma (Ouimet et al, 2010).…”

“…This value is comparable to the measured incision rates (10-90 m. Myr -1 ) by cosmogenic 26 Al dating of the Wudingshan caves (with burial ages of 2.54 and 0.69 Ma) in close proximity of the northern end of the Red River (Schoenbohm, 2004b). The incision rate estimated from sites B-D, however, are much lower than those obtained from the Nanpie River and other deeply incised rivers over the Yunnan Plateau (Allen et al, 1984;Kirby et al, 2003;Clark et al, 2005;Ouimet et al, 2010;Godard et al, 2010;Duvall et al, 2012;Hetzel, 2013), implying distinct drainage incision in different time periods, likely due to changes in climatic conditions or staged tectonic uplift of the plateau (Schoenbohm et al, 2004a). It is noticeable that there is an absence of alluvium sediments over saprolites at the lower-elevation sites C and D, indicating that the relict terraces of the Nanpie River have experienced different stages of drainage incision since ~3 Ma.…”

Tectonic control of Yarlung Tsangpo Gorge revealed by a buried canyon in Southern Tibet

“…These samples were sent to the Cosmogenic Nuclide Laboratory of the European Center for Earth Sciences, Environment Research and Education (CEREGE) in France for target preparation and measurement of the 10 Be/ 9 Be and 26 Al/ 27 Al ratios (Table S2). The ratios were measured relative to the standard NIST4325 with a nominal 10 Be/ 9 Be ratio of 2.79 × 10 -11 , and SM-Al-11, with a nominal 26 Al/ 27 Al ratio of 7.401 × 10 -12 . Our process blank 10 Be/ 9 Be ratio was 2.7 × 10 -15 and the corresponding 10 Be atoms were subtracted from the reported sample results.…”

“…Residual impurities were removed by heavy-liquid and hand separation under the microscope and the samples were once more treated with diluted HF/HNO 3 solution and dried. Aliquots of two grams were taken from each sample, dissolved in concentrated HF/HNO 3 and analysed by Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) measurements for 27 Al and other elements to assure purity. The remaining quartz was spiked with 0.25 mg of 9 Be in a weak HNO 3 carrier solution, and then heated and dissolved.…”

Erosion in southern Tibet shut down at ∼10 Ma due to enhanced rock uplift within the Himalaya

“…Because externally drained rivers provide an erosive mechanism to destroy uplifted terrane, understanding why these rivers have not incised further and more deeply into the Tibetan plateau is essential to decipher how the plateau grew. Recent research in the eastern (7,8) and northern (9) Tibetan plateau indicates that erosion rates have increased significantly since ∼10 Ma. These increases suggest that rock uplift rates have also increased and that the plateau has expanded to the east and north during this time [due to lower crustal flow (7) or upper crustal extrusion (8) to the east and structural reorganization to the north (9)], causing rivers to steepen and erode at faster rates.…”