282 research outputs found
Early Holocene collapse of Volcan Parinacota, central Andes, Chile: Volcanological and paleohydrological consequences
No full textThe catastrophic gravitational collapse of the Old Cone of Volcan Parinacota produced a 6 km(3) debris avalanche that traveled similar to 22 km and covered more than 150 km(2). The Upper Lauca drainage, a broad high-altitude basin in the Chilean Altiplano, was permanently altered by the collapse. Although the eruptive history of Parinacota before and after-the debris avalanche is well known from petrologic and geochronologic studies, previous age limits on the debris avalanche (based on multiple chronometers) span ca. 8-20 ka. New cosmogenic surface-exposure ages from boulders atop the deposit are based on a regionally calibrated production rate of in situ Be-10 and indicate that the avalanche occurred at 8.8 +/- 0.5 ka. These data demonstrate that cosmogenic 10Be surface-exposure dating can be successfully applied to quartz-bearing, volcanic debris avalanche deposits, and that this method offers a distinct advantage over C-14 chronologies that provide only minimum or maximum age limits. The 8.8 ka exposure age for the debris avalanche (1) agrees with 14C age limits of paleosol material incorporated in the debris avalanche, (2) requires a voluminous initial phase of postcollapse volcanism with an eruptive rate exceeding that of recent cone-building episodes at most continental arc volcanoes, and (3) suggests that volcano collapse did not result in the formation of Lago Chungara, but instead led to a major expansion of a preexisting closed basin
Cosmogenic nuclides: Beryllium-10 and Chlorine-36 in the West Antarctic Ice Sheet Divide ice core and advances in accelerator
No full textPolar ice cores continue to provide a wealth of information about the history of Earth\u27s environment. Cosmogenic radionuclides, produced in the atmosphere by cosmic rays and deposited on ice sheets, carry clues to the nature and variability of solar activity and the geomagnetic field in the past. They can also be used to independently measure the snow accumulation rate and provide chronological markers to compare with other paleoarchives such as sea sediment cores. The present work details measurements of 10Be and 36Cl in the West Antarctic Ice Sheet Divide ice core. We have established a new chemical processing line at Purdue University for this work and demonstrated that it produces results identical to a sister lab at UC Berkeley. 10Be and 36Cl have been measured in the top 560 m of core at ∼12 and 24 year resolution. In addition we have measured 10Be at annual resolution from 1586–2006 AD. We find good agreement between our results and a 10Be record from Greenland and with the historic sunspot record. In addition, work is described on the development of several new upgrades to the Purdue Rare Isotope Measurement Lab accelerator mass spectrometry facility. Two new detectors for 14C and 10Be have been constructed as well as a new gas-filled magnet system. The new detectors have capabilities comparable to those of the previous detector and have been easier and faster to use. The gas-filled magnet system is not yet ready for routine use but preliminary tests have been performed and further development of the system is underway
Cosmogenic Ages from Alluvial Fans offset by Central Walker Lane Faults
No full textHere are a series of cosmogenic 10Be and 36Cl ages and metadata for samples related to a faulting study southeast of Reno, NV, USA. Both 10Be and 36Cl concentrations were measured at the PRIME lab at Purdue. All 10Be samples were processed in the Geochronology Laboratories at the University of Cincinnati. The 36Cl samples were processed and analyzed at the PRIME lab. Boulder sampling focused on the largest boulders (~50–150-cm-diameter) from alluvial fan surfaces. Approximately 500 g samples were taken from the upper 2–5 cm of each of these boulders. 10Be concentrations and laboratory data are listed in these tables. The 10Be boulder exposure ages were calculated using the Cosmic Ray Exposure Program (CREp). The calculator requires input describing the geographic coordinates and elevation of the samples, local shielding of the sample, density of the sample, and estimation of the boulder erosion rates resulting from processes such as boulder grussification and spalling. The age estimates are also dependent on the assumption of particular scaling models designed to estimate the long-term production rate of cosmogenic 10Be. The 10Be ages use a production rate of 4.05 ± 0.30 at/g SiO2/yr determined at Twin Lakes, which is located at a higher elevation than the fan surfaces here, but is within 100 km of all study sites, the ERA40 atmosphere model, the Lifton-VDM2016 geomagnetic database, and the LSD scaling scheme.The 36Cl boulder ages are calculated using the CRONUS calculator for 36Cl
Sample preparation and laboratory measurement values for coarse-grain meteoric Beryllium 10 concentrations before and after Hurricane Maria in Dominica and the percent difference between the two time periods
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Detrital in situ and meteoric Beryllium 10 measurements from samples taken before and after Hurricane Maria in Dominica
No full textTropical islands, including many in island arcs, are susceptible to recurring disturbances from extreme storms. To test whether such storms bias isotopic indicators of long-term erosion, we measured 10Be in samples collected before and after Hurricane Maria (2017, category five) from Dominica, an andesitic island in the Caribbean. Populations of before- and after-storm concentrations of 10Be are indistinguishable (n = 7 for in situ, n = 11 for meteoric); however, individual sample sites replicate less well with isotopic concentrations in samples taken before and after the storm varying by an average of 12%. These data suggest that processes controlling the depth and amount of near-surface erosion on Dominica during extreme storms are stochastic. Erosion rates determined from in situ 10Be are low compared to similarly steep and wet areas (median = 0.082 mm/yr, n = 12) and appear to be controlled by orographic precipitation
CRONUS-Earth cosmogenic 36Cl calibration
No full textChlorine-36 production rates obtained from different geological calibration studies (e.g. Evans et al., 1997; Phillips et al., 2001; Schimmelpfennig et al., 2011; Stone et al., 1996; Swanson and Caffee, 2001) vary significantly, principally because of the many reactions contributing to the production of this nuclide. The CRONUS-Earth Project has provided high-quality geological calibration sites, including Lake Bonneville, Peru, and Scotland, for a large-scale calibration of 36Cl production rates. Three sites were used to calibrate the K and Ca spallation pathways for 36Cl production yielding production rates of 56.0 ± 4.1 at 36Cl (g Ca)−1 yr−1 and 155 ± 11 at 36Cl (g K)−1 yr−1 respectively, using Lifton-Sato-Dunai scaling (LSDn). The low-energy production parameter, Pf(0), was calibrated separately using CRONUS-Earth data from the Bonneville and Baboon Lakes sites where Cl concentrations were higher, and yielded a value of 759 ± 180 neutrons (g air)−1 yr−1. There is significant uncertainty associated with this pathway due to the sensitivity of this reaction to environmental conditions. The uncertainties associated with the calibrated production parameters were estimated based on the variance of calculated ages from independent ages for an independent secondary dataset
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