Dynamics of marine sediments studied through 10Be

Dynamics of marine sediments studied through 10Be

Rodrigues, D.; Arazi, A.; Korschinek, G.; Martí, G. V.; Merchel, S.; Rugel, G.

Marine sediments may originate from the erosion of continental material (containing both cosmogenic 10Be, and 9Be with a ratio around 10-8) that has been carried by rivers to the sea. If the sediments are deposited in zones where a tectonic plate subducts beneath another one, they might follow complex processes, in which part of the sediments are dragged under the plate and the other part is accreted above.

In this work, depth profiles of the 10Be/9Be ratios in marine sediments are being studied near the spot where Nazca, Antarctica and South American tectonic plates join each other.
A preliminary set of seven samples, provided by the Ocean Drill Project [1], were measured at the DREAMS facility [2]; this represents the first measurement of a depth profile near this zone. The isotopic ratios, based on AMS-measurements of 10Be/9Be and determinations of 9Be concentration performed by ICP-MS at HZDR are ranging from 4.9 to 53 x 10-9. Contrary to the expectation they do not decrease with depth, but rise into the interval corresponding to 102 to 145 meters of depth, and from 197 to 256 meters of depth. We show that this result is consistent with a reverse (thrust) fault in the sediments due to the compression pressure exerted by the subduction of the Nazca tectonic plate.

[1] Behrmann et al. Proceedings of the Ocean Drilling Program, Initial Reports, 141, (1992).
[2] Akhmadaliev et al. Nucl. Instr. and Meth. in Physics Research B, 294, 5-10 (2013).

Keywords: accelerator mass spectrometry; cosmogenic nuclide; tectonics

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