Differences in 10Be concentrations between river sand, gravel and pebbles along the western side of the central Andes

Carretier, Sébastien; Regard, Vincent; Vassallo, Riccardo; Aguilar, Germán; Martinod, Joseph; Riquelme, Rodrigo; Christophoul, Frédéric; Charrier, Reynaldo; Gayer, Éric; Farías, Marcelo; Audin, Laurence; Lagane, Christelle

doi:10.1016/j.quageo.2014.12.002

Cited by 48 publications

(50 citation statements)

References 80 publications

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“…Our numerical simulations using empirically derived abrasion rates agree with recent research that highlights grain size biasing as one of the factors controlling the mineralogy and, therefore, the grain information of sands transported by rivers (e.g., Aguilar et al, ; Carretier et al, ; Codilean et al, ). The importance of abrasion in distorting grain age distributions is, however, more debatable.…”

Section: Discussionsupporting

confidence: 87%

Does Pebble Abrasion Influence Detrital Age Population Statistics? A Numerical Investigation of Natural Data Sets

et al. 2018

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Pebble abrasion is a key factor controlling the release of minerals into sand, but few attempts have been made to model how it could influence the liberation of minerals into the size fraction used in detrital geochronology. We perform a series of experiments with an abrasion model to test this influence using natural and synthetic data sets. Our results demonstrate that pebble abrasion can change the zircon mixing proportions of upstream source units as well as the age distribution of mixed fluvial sands. This change is particularly significant when there is strong contrast in rock resistance within the watershed. Pebble abrasion is one of many factors that can change the mixing proportion of sands, including hillslope gravel supply, erosion rates, and mineral fertility. In our study case (Marsyandi watershed, Himalaya), the abrasion model predicts age distributions that are statistically indistinguishable from those predicted by a no‐abrasion model. However, the relative erosion rates estimated by our model largely differ from the results of a no‐abrasion model and are closer to those from other studies that suggest a strong correlation between modern erosion rates, tectonics, and precipitation intensity in the Marsyandi watershed. These findings highlight that, even in cases where there is no statistical evidence of change between the modeled age distributions, abrasion can affect the erosion rates estimated from them. Therefore, quantifying the influence of abrasion on sand production is an essential step not only to predict mixing proportions but also to accurately retrieve erosion rates from the measured grain age distributions.

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Section: Discussionsupporting

confidence: 87%

Does Pebble Abrasion Influence Detrital Age Population Statistics? A Numerical Investigation of Natural Data Sets

et al. 2018

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“…For the moment, the absence of database or theoretical models of these processes prevents detailed exploration of the sand size issue. Our simplified model could actually only be validated or invalidated by comparing 10 Be concentration across a large range of grain sizes, i.e., between sand size content and boulder size similar to what has been done by Puchol et al (2014) and Carretier et al (2015b), who found lower 10 Be concentrations in pebble-sized sediments.…”

Section: Abrasion Of Landslide Materialsmentioning

confidence: 85%

<sup>10</sup>Be systematics in the Tsangpo-Brahmaputra catchment: the cosmogenic nuclide legacy of the eastern Himalayan syntaxis

Lupker¹,

Lavé²,

France‐Lanord

et al. 2017

Earth Surf. Dynam.

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Abstract. The Tsangpo-Brahmaputra River drains the eastern part of the Himalayan range and flows from the Tibetan Plateau through the eastern Himalayan syntaxis downstream to the Indo-Gangetic floodplain and the Bay of Bengal. As such, it is a unique natural laboratory to study how denudation and sediment production processes are transferred to river detrital signals. In this study, we present a new 10 Be data set to constrain denudation rates across the catchment and to quantify the impact of rapid erosion within the syntaxis region on cosmogenic nuclide budgets and signals. The measured 10 Be denudation rates span around 2 orders of magnitude across individual catchments (ranging from 0.03 to > 4 mm yr −1 ) and sharply increase as the Tsangpo-Brahmaputra flows across the eastern Himalaya. The increase in denudation rates, however, occurs ∼ 150 km downstream of the Namche Barwa-Gyala Peri massif (NBGPm), an area which has been previously characterized by extremely high erosion and exhumation rates. We suggest that this downstream lag is mainly due to the physical abrasion of coarse-grained, low 10 Be concentration, landslide material produced within the syntaxis that dilutes the upstream high-concentration 10 Be flux from the Tibetan Plateau only after abrasion has transferred sediment to the studied sand fraction. A simple abrasion model produces typical lag distances of 50 to 150 km compatible with our observations. Abrasion effects reduce the spatial resolution over which denudation can be constrained in the eastern Himalayan syntaxis. In addition, we also highlight that denudation rate estimates are dependent on the sediment connectivity, storage, and quartz content of the upstream Tibetan Plateau part of the catchment, which tends to lead to an overestimation of downstream denudation rates. While no direct 10 Be denudation measurements were made in the syntaxis, the dilution of the upstream 10 Be signal, measured in Tsangpo-Brahmaputra sediments, provides constraints on the denudation rates in that region. These denudation estimates range from ca. 2 to 5 mm yr −1 for the entire syntaxis and ca. 4 to 28 mm yr −1 for the NBGPm, which is significantly higher than other large catchments. Overall, 10 Be concentrations measured at the outlet of the Tsangpo-Brahmaputra in Bangladesh suggest a sediment flux between 780 and 1430 Mt yr −1 equivalent to a denudation rate between 0.7 and 1.2 mm yr −1 for the entire catchment.

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“…More recent, shorter timescale denudation rates (<~10 6 years) based on catchment‐averaged 10 Be, 26 Al, and 21 Ne cosmogenic nuclide concentrations and exposure ages have been reported, as low as <1 m/Myr, up to several orders of magnitude lower than bedrock thermochronometric exhumation rates in the southern Peruvian and northern Chilean fore arc but range up to 300 m/Myr (~0.3 km/Myr) at higher elevations and slopes, particularly in the modern‐day Precordillera (Abbühl et al, 2010, 2011; Carretier, Regard, Vassallo, Aguilar, et al, 2015; Carretier, Regard, Vassallo, Martinod, et al, 2015; Kober et al, 2007, 2009; McPhillips et al, 2013; Placzek et al, 2010; Starke et al, 2017). Generally, higher rates are reported in southern Peru than in northern Chile but correlations with precipitation or hillslope angles are inconsistent (Abbühl et al, 2011; Kober et al, 2009; Reber et al, 2017; Starke et al, 2017) and extreme climatic events (e.g., El Niño) may be important (Abbühl et al, 2010).…”

Section: Discussionmentioning

confidence: 99%

Slow Long‐Term Exhumation of the West Central Andean Plate Boundary, Chile

2018

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We present a regional analysis of new low‐temperature thermochronometer ages from the Central Andean fore arc to provide insights into the exhumation history of the western Andean margin. To derive exhumation rates over 10 million‐year timescales, 38 new apatite and zircon (U‐Th)/He ages were analyzed along six ~500‐km long near‐equal‐elevation, coast parallel, transects in the Coastal Cordillera (CC) and higher‐elevation Precordillera (PC) of the northern Chilean Andes between latitudes 18.5°S and 22.5°S. These transects were augmented with age‐elevation profiles where possible. Results are synthesized with previously published thermochronometric data, corroborating a previously observed trenchward increase in cooling ages in Peru and northern Chile. One‐dimensional thermal‐kinematic modeling of all available multichronometer equal‐elevation samples reveals mean exhumation rates of <0.2 km/Myr since ~50 Ma in the PC and ~100 Ma in the CC. Regression of pseudovertical age‐elevation transects in the CC yields comparable rates of ~0.05 to ~0.12 km/Myr between ~40 and 80 Ma. Differences between the long‐term mean 1‐D rates and shorter‐term age‐elevation‐derived rates indicate low variability in the exhumation history. Modeling results suggest similar background exhumation rates in the CC and PC; younger ages in the PC are largely a function of increased heat flow and consequently an elevated geothermal gradient near the arc. Slow exhumation rates are suggestive of semiarid conditions across the region since at least the Eocene and deformation and development of the Andean fore arc around this time.

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Differences in 10Be concentrations between river sand, gravel and pebbles along the western side of the central Andes

Cited by 48 publications

References 80 publications

Does Pebble Abrasion Influence Detrital Age Population Statistics? A Numerical Investigation of Natural Data Sets

Does Pebble Abrasion Influence Detrital Age Population Statistics? A Numerical Investigation of Natural Data Sets

<sup>10</sup>Be systematics in the Tsangpo-Brahmaputra catchment: the cosmogenic nuclide legacy of the eastern Himalayan syntaxis

Slow Long‐Term Exhumation of the West Central Andean Plate Boundary, Chile

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Differences in 10Be concentrations between river sand, gravel and pebbles along the western side of the central Andes

Cited by 48 publications

References 80 publications

Does Pebble Abrasion Influence Detrital Age Population Statistics? A Numerical Investigation of Natural Data Sets

Does Pebble Abrasion Influence Detrital Age Population Statistics? A Numerical Investigation of Natural Data Sets

&lt;sup&gt;10&lt;/sup&gt;Be systematics in the Tsangpo-Brahmaputra catchment: the cosmogenic nuclide legacy of the eastern Himalayan syntaxis

Slow Long‐Term Exhumation of the West Central Andean Plate Boundary, Chile

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<sup>10</sup>Be systematics in the Tsangpo-Brahmaputra catchment: the cosmogenic nuclide legacy of the eastern Himalayan syntaxis