Fuerteventura - Assessment of a calibration site for cosmogenic He-3 exposure dating with the Ar-40/Ar-39 incremental heating method

Autor: F.M. Stuart, B.S.H. Schneider, J.P.T. Foeken, Klaudia F. Kuiper, K. Mai, Jan R. Wijbrans
Přispěvatelé: Geology and Geochemistry, Isotope Geochemistry
Jazyk: angličtina
Rok vydání: 2014
Předmět:
Zdroj: Quaternary Geochronology, 21, 58-69. Elsevier
Schneider, B S H, Kuiper, K F, Mai, K, Foeken, J P T, Stuart, F M & Wijbrans, J R 2014, ' Fuerteventura-Assessment of a calibration site for cosmogenic He-3 exposure dating with the Ar-40/Ar-39 incremental heating method ', Quaternary Geochronology, vol. 21, pp. 58-69 . https://doi.org/10.1016/j.quageo.2013.09.005
ISSN: 1871-1014
DOI: 10.1016/j.quageo.2013.09.005
Popis: In situ Terrestrial Cosmogenic Nuclides (hereafter TCNs) are increasingly important for absolutely dating terrestrial events and processes. This study aimed at improving our knowledge of the production rate of Terrestrial Cosmogenic 3 He formed in situ in rock surfaces at low latitude and sea level as well as re-evaluation of the Canary Islands as a calibration site for TCNs. For this purpose, we sampled basaltic lava flows from some of the youngest and yet undated volcanic sites and used the 40 Ar/ 39 Ar incremental heating method on groundmass samples and in situ cosmogenic 3 He on olivine and clinopyroxene phenocrysts. 40 Ar/ 39 Ar analysis was done on a Hiden HAL Series 1000 triple filter quadrupole mass spectrometer with extraction furnace. Incremental heating data shows ages in the Late Pleistocene from 52.7 ± 21.6 ka to 398.6 ± 27.6 ka. We measured cosmogenic 3 He concentrations in olivine and clinopyroxene phenocrysts from flow top samples on a MAP 215-50 sector mass spectrometer with a crushing device and a diode laser extraction system. Exposure age calculations yielded ages in the range 38.9 ± 4.0 ka to 62.3 ± 6.7 ka for the youngest lava flow and the data series is in broad agreement with the argon data up to 250 ka and reveals a more continuous time line of volcanism during the late Pleistocene on the island. However, the dataset was not sufficient for calculation of production rates for in situ Terrestrial Cosmogenic 3 He as many samples showed signs of erosion. Calculated erosion rates range from none to as high as 7.3 mm/kyr assuming a rock density of 2.9 g/cm 2 . This finding puts a constraint on the use of Fuerteventura as a calibration site for exposure histories older than 50–100 ka. A comparison with cosmogenic 36 Cl data supports these findings and indicates substantial weathering.
Databáze: OpenAIRE
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