Erosion rates of the Bhutanese Himalaya determined using in situ-produced 10Be

Portenga, Eric W.; Bierman, Paul R.; Duncan, Charles H.; Corbett, Lee B.; Kehrwald, Natalie; Rood, Dylan H.

doi:10.1016/j.geomorph.2014.09.027

Cited by 65 publications

(99 citation statements)

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“…Since glacial ice intercepts, and thus shields underlying material from cosmic radiation, previously and currently glaciated basins may violate the isotopic equilibrium assumption if ice was present recently, and erosion has not been able to remove the older shielding signal (Moon et al, 2011;Portenga et al, 2014;Vance et al, 2003). Therefore, interpreting cosmogenic nuclide concentrations as direct measurements of erosion in some glaciated landscapes can lead to overestimated rates (Gosse and Phillips, 2001;Vance et al, 2003;Portenga et al, 2014). 175…”

Section: Isotopic Equilibrium Modelingmentioning

confidence: 99%

Tectonic controls of Holocene erosion in a glaciated orogen

Adams¹,

Ehlers²

2018

Preprint

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Abstract. Recent work has highlighted a strong, worldwide, glacial impact of orogen erosion rates over the last 2 Ma. While it may be assumed that glaciers increased erosion rates when active, the degree to which past glaciations influence Holocene erosion rates through the adjustment of topography is not known. In this study, we investigate the influence of long-term tectonic and post-glacial topographic controls on erosion in a glaciated orogen, the Olympic Mountains, USA. We present 14 10 new 10 Be and 26 Al analyses which constrain Holocene erosion rates across the Olympic Mountains. Basin-averaged erosion rates scale with basin-averaged values of 5-km local relief, channel steepness, and hillslope angle throughout the range, similar to observations from non-glaciated orogens. These erosion rates are not related to mean annual precipitation or the marked change in Pleistocene alpine glacier size across the range, implying that glacier modification of topography and modern precipitation parameters do not exert strong controls on these rates. Rather, we find that despite intense spatial variations in 15 glacial modification of topography, patterns of recent erosion are similar to those from estimates of long-term tectonic rock uplift. This is consistent with a tectonic model where erosion and rock uplift patterns are controlled by the deformation of the Cascadia subduction zone.

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Section: Isotopic Equilibrium Modelingmentioning

confidence: 99%

Tectonic controls of Holocene erosion in a glaciated orogen

Adams¹,

Ehlers²

2018

Preprint

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“…Increasing the 18 precision of analyses enhances not only the interpretations that can be made from dates and rates, 19 but also enables approaches involving multiple isotopic systems such as burial dating (Granger 20 and Muzikar, 2001) and burial isochron dating (Balco and Rovey, 2008), and allows for 21 improved calibration of cosmogenic nuclide production rates (Balco et al, 2009;Borchers et al, 22 2015; Briner et al, 2012;Putnam et al, 2010). Very low concentration samples, such as those 23 from young exposures (Licciardi et al, 2009), rapidly eroding landscapes (Portenga et al, 2015), 1 or long-buried sediments (Erlanger et al, 2012;Gibbon et al, 2014), require low detection limits 2 to be measurable above background levels. High 9 Be 3+ beam currents reduce the counting times 3 required to achieve desired precisions, thereby speeding AMS throughput and better utilizing the 4 limited beam time available for analysis.…”

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confidence: 99%

“…Analysis of post-dissolution aliquots (Fig. 5) quantifies if any native 9 Be is present in the 19 quartz (Portenga et al, 2015), while analysis of post-processing aliquots (Fig. 6) serves as a 20 quality control metric to assess final Be yield and ensure that all samples have consistent Be 21 mass (Hunt et al, 2008).…”

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confidence: 99%

“…For example, in a suite of 49 5 samples from Bhutan prepared at University of Vermont, most samples contained detectable 6 native 9 Be (Portenga et al, 2015). Approximately 240 μg of 9 Be carrier was added to each of the grains, and/or structural substitution in quartz grains (Grew, 2002).…”

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confidence: 99%

“…Improved AMS techniques now consistently 11 produce machine blanks with 10 Be/ 9 Be ratios well below 10 -15 (Rood et al, 2010), placing 12 greater demands on processing laboratories to both minimize sample cross-talk and lower the 13 amount of the interfering isobar, 10 B. (Licciardi et al, 2009), those that have been subjected to rapid erosion (Portenga et al, 2015), or 22 those that have been buried for long durations (Erlanger et al, 2012;Gibbon et al, 2014). Grant (BCS-1433878).…”

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confidence: 99%

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An approach for optimizing in situ cosmogenic 10Be sample preparation

Corbett

Bierman

Rood

2016

Quaternary Geochronology

Self Cite

143

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Optimizing sample preparation for the isotopic measurement of 10Be extracted from quartz mineral separates has a direct positive effect on the efficiency of sample production and the accuracy and precision of isotopic analysis. Here, we demonstrate the value of tracing Be throughout the extraction process (both after dissolution and after processing), producing pure Be (by optimizing column chromatography methods and quantifying quartz mineral separate purity), and minimizing backgrounds (through reducing both laboratory process blanks and 10B isobaric interference). These optimization strategies increase the amount of 10Be available for analysis during accelerator mass spectrometry (AMS), while simultaneously decreasing interference and contamination, and ensuring that sample performance matches standard performance during analysis. After optimization of our laboratory's extraction methodology, 9Be3+ beam currents, a metric for sample purity and Be yield through the extraction process, matched the 9Be3+ beam currents of AMS standards analyzed at the same time considering nearly 800 samples. Optimization of laboratory procedures leads to purer samples that perform better, more consistently, and more similarly to standards during AMS analysis, allowing for improved dating and quantification of Earth surface processes. February 2, 2016To the Editor:After performing the revisions suggested by two reviewers, we are resubmitting our manuscript, An Approach for Optimizing In Situ Cosmogenic 10 Be Sample Preparation, for publication in Quaternary Geochronology.We appreciated the comments from both reviewers and found that their suggestions improved the manuscript. In our revisions, we focused particular attention toward broadening our discussion of measurement accuracy, clarifying the impact of Ti impurities in samples, providing more information about beam current normalization, and benchmarking our methods against those previously used in our laboratory. As a group, we considered each suggestion and addressed it in the way that we thought most benefited the manuscript. In the following pages, you will find a list of the reviewers' suggestions and details about how we incorporated those suggestions.We are optimistic that our revisions have addressed the reviewers' concerns and that the manuscript has grown in both clarity and applicability. Thank you in advance for considering our revised draft. The paper of Corbett et al. describes in detail the chemical separation procedure for Be-10 in quartz samples applied at the University of Vermont. They show how their column chemistry was optimized for the purification of Be and they impressively demonstrate, on the statistical base of about 800 samples, that their lab constantly produces high quality Be-10 samples. This paper is important not only for newcomers in the field, e.g. who want to set up their own lab, but also for the existing cosmo labs because it demonstrates the importance of quality control e.g. to avoid systematic errors in the final Be-10 ages. D...

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Evidence for a wide and gently dipping Main Himalayan Thrust in western Bhutan

Roux-Mallouf

Godard

Cattin

et al. 2015

Geophysical Research Letters

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The Main Himalayan Thrust (MHT) is the source of great earthquakes that have been documented along the range. Its geometry is a key parameter that influences accommodation of tectonic loading and earthquake magnitudes along the Himalayan Arc. Although seismic images are available for both the western and the central part of the range, this geometry remains poorly constrained for the Bhutanese Himalayas. Here we address this issue using a 10Be cosmogenic nuclides denudation transect across western Bhutan. We observe a wide low denudation rate domain between 50 km and 110 km from the front followed by a strong northward increase. Using a joint inversion of denudation rates, GPS data, and Holocene uplift rates, we interpret this pattern as a consequence of a flat‐ramp transition along the MHT. Compared to central Nepal and Sikkim, this location of the ramp suggests a wider décollement, with implications for greater seismogenic potential of the MHT in western Bhutan.

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Erosion rates of the Bhutanese Himalaya determined using in situ-produced 10Be

Cited by 65 publications

References 101 publications

Tectonic controls of Holocene erosion in a glaciated orogen

Tectonic controls of Holocene erosion in a glaciated orogen

An approach for optimizing in situ cosmogenic 10Be sample preparation

Evidence for a wide and gently dipping Main Himalayan Thrust in western Bhutan

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