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Nitrogen recycling at the Costa Rican subduction zone: The role of incoming plate structure.


ABSTRACT: Efficient recycling of subducted sedimentary nitrogen (N) back to the atmosphere through arc volcanism has been advocated for the Central America margin while at other locations mass balance considerations and N contents of high pressure metamorphic rocks imply massive addition of subducted N to the mantle and past the zones of arc magma generation. Here, we report new results of N isotope compositions with gas chemistry and noble gas compositions of forearc and arc front springs in Costa Rica to show that the structure of the incoming plate has a profound effect on the extent of N subduction into the mantle. N isotope compositions of emitted arc gases (9-11?N°) imply less subducted pelagic sediment contribution compared to farther north. The N isotope compositions (?15N?=?-4.4 to 1.6‰) of forearc springs at 9-11?N° are consistent with previously reported values in volcanic centers (?15N?=?-3.0 to 1.9‰). We advocate that subduction erosion enhanced by abundant seamount subduction at 9-11?N° introduces overlying forearc crustal materials into the Costa Rican subduction zone, releasing fluids with lighter N isotope signatures. This process supports the recycling of heavier N into the deep mantle in this section of the Central America margin.

SUBMITTER: Lee H 

PROVIDER: S-EPMC5654979 | BioStudies | 2017-01-01T00:00:00Z

REPOSITORIES: biostudies

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