Recycling of subducted sediments at the Southern Andes studied by AMS measurements of 10Be concentrations

D. RODRIGUES ; A. ARAZI ; E. CHAMIZO, ; D. FRACCHIA, ; J.M. LÓPEZ-GUTIÉRREZ, ; S. PADILLA, ; J. FERNÁNDEZ NIELLO, ; G. KORSCHINEK, ; G. MARTÍ, ; A. NEGRI, ; E. DEBARBARÁ, ; D. ABRIOLA, ; O. CAPURRO, ; M.A. CARDONA, ; D. HOJMAN, ; F. GOLLAN, ; A. PACHECO, ; D. SAAD, ; N. SAMSOLO, ; M. TOGNERI, ; D.VILLANUEVA

Ottawa

Conferencia; The 14th International Conference on Accelerator Mass Spectrometry; 2017

University of Ottawa

The subduction of an oceanic plate beneath a continental plate may be accompanied with accretion of marine sediments at the border of the continent or with their dragging down into the Earths?s mantle. In the second case, a fraction of the subducted sediments can be incorporated into magmas and then erupt in the form ofarc volcanic rocks or ashes in periods of a few million years. Hence, cosmogenic 10Be is a suitable tracer for this process. We present measurements of 10Be concentrations in marine sediments at the Chile trench, in arc volcanic ashes from the Southern Andes and in an intraplate basalt at the same latitude. Volcanic ashes and the intraplate basalt sample were studied at the 1 MV SARA facility in Sevilla, where the interfering 10B was suppressed using a silicon nitride passive absorber, a 120° electrostatic analyzer and a gas-gas telescopedetector. Volcanic ashes yielded values in the order of 107 atoms/g, while the intraplate basalt blank less than 2 x 106 atoms/g. The measurements of 10Be concentrations in sediments were performed at the 20 UD TANDAR Accelerator in Buenos Aires. In this facility, the high energy available (27 MeV) allowed the discrimination of 10Be ions by means of a passive argon absorber (with Havar foil windows), which completely stops 10B ions, and a gas-solid telescope detector. 10Be concentration values of the order of 109 atoms/g were obtained. The present data, analysed in the framework of a model for the subduction process, allowed us to estimate that a fraction between 9% and 22% of marine sediments are recycled during the subduction. These measurements show the feasibility of the TANDAR Accelerator for AMS measurements at terminal voltages of about 8 to 10 MV. Several improvements, including the commissioning of a Wien filter and a 6.7 m-long time of flight system, will also be reported.