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dc.contributor.authorHalama, Ralf  Concept link
dc.contributor.authorBebout, Gray  Concept link
dc.contributor.authorMarschall, Horst R.  Concept link
dc.contributor.authorJohn, Timm  Concept link
dc.date.accessioned2017-05-17T18:51:51Z
dc.date.issued2016-09
dc.identifier.urihttps://hdl.handle.net/1912/8985
dc.descriptionAuthor Posting. © The Author(s), 2016. This is the author's version of the work. It is posted here by permission of Taylor & Francis for personal use, not for redistribution. The definitive version was published in International Geology Review 59 (2017): 702-720, doi:10.1080/00206814.2016.1233834.en_US
dc.description.abstractIn order to determine the effects of fluid–rock interaction on nitrogen elemental and isotopic systematics in high-pressure metamorphic rocks, we investigated three different profiles representing three distinct scenarios of metasomatic overprinting. A profile from the Chinese Tianshan (ultra)high-pressure–low-temperature metamorphic belt represents a prograde, fluid-induced blueschist–eclogite transformation. This profile shows a systematic decrease in N concentrations from the host blueschist (~26 μg/g) via a blueschist–eclogite transition zone (19–23 μg/g) and an eclogitic selvage (12–16 μg/g) towards the former fluid pathway. Eclogites and blueschists show only a small variation in δ15Nair (+2.1 ± 0.3‰), but the systematic trend with distance is consistent with a batch devolatilization process. A second profile from the Tianshan represents a retrograde eclogite–blueschist transition. It shows increasing, but more scattered, N concentrations from the eclogite towards the blueschist and an unsystematic variation in δ15N values (δ15N = + 1.0 to +5.4‰). A third profile from the high-P/T metamorphic basement complex of the Southern Armorican Massif (Vendée, France) comprises a sequence from an eclogite lens via retrogressed eclogite and amphibolite into metasedimentary country rock gneisses. Metasedimentary gneisses have high N contents (14–52 μg/g) and positive δ15N values (+2.9 to +5.8‰), and N concentrations become lower away from the contact with 11–24 μg/g for the amphibolites, 10–14 μg/g for the retrogressed eclogite, and 2.1–3.6 μg/g for the pristine eclogite, which also has the lightest N isotopic compositions (δ15N = + 2.1 to +3.6‰). Overall, geochemical correlations demonstrate that phengitic white mica is the major host of N in metamorphosed mafic rocks. During fluid-induced metamorphic overprint, both abundances and isotopic composition of N are controlled by the stability and presence of white mica. Phengite breakdown in high-P/T metamorphic rocks can liberate significant amounts of N into the fluid. Due to the sensitivity of the N isotope system to a sedimentary signature, it can be used to trace the extent of N transport during metasomatic processes. The Vendée profile demonstrates that this process occurs over several tens of metres and affects both N concentrations and N isotopic compositions.en_US
dc.description.sponsorshipSupport of this project was partly provided by National Science Foundation grant EAR-0711355 to GEB.en_US
dc.language.isoenen_US
dc.relation.urihttps://doi.org/10.1080/00206814.2016.1233834
dc.subjectNitrogenen_US
dc.subjectN isotopesen_US
dc.subjectWhite micaen_US
dc.subjectFluid-rock interactionen_US
dc.subjectSubductionen_US
dc.subjectHigh-pressure metamorphic rocksen_US
dc.titleFluid-induced breakdown of white mica controls nitrogen transfer during fluid–rock interaction in subduction zonesen_US
dc.typePreprinten_US
dc.description.embargo2017-10-10en_US
dc.embargo.liftdate2017-10-10


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