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  Boron as a tracer for material transfer in subduction zones

Rosner, M. S. (2004): Boron as a tracer for material transfer in subduction zones, PhD Thesis, (Scientific Technical Report STR ; 04/09), Potsdam : Deutsches GeoForschungsZentrum GFZ, 104 S.  p.
URN: http://nbn-resolving.de/urn/resolver.pl?urn=urn:nbn:de:kobv:b103-04091

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Datensatz-Permalink: https://gfzpublic.gfz-potsdam.de/pubman/item/item_8638 Versions-Permalink: https://gfzpublic.gfz-potsdam.de/pubman/item/item_8638_6
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 Urheber:
Rosner, Martin Siegfried1, 2, Autor
Affiliations:
1Scientific Technical Report STR, Deutsches GeoForschungsZentrum, ou_9026              
24.2 Inorganic and Isotope Geochemistry, 4.0 Chemistry and Material Cycles, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum, ou_146040              

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 Zusammenfassung: Late Miocene to Quaternary volcanic rocks from the frontal arc to the back-arc region of the Central Volcanic Zone in the Andes show a wide range of delta 11B values (+4 to -7 ‰) and boron concentrations (6 to 60 ppm). Positive delta 11B values of samples from the volcanic front indicate involvement of a 11B-enriched slab component, most likely derived from altered oceanic crust, despite the thick Andean continental lithosphere, and rule out a pure crust-mantle origin for these lavas. The delta 11B values and B concentrations in the lavas decrease systematically with increasing depth of the Wadati-Benioff Zone. This across-arc variation in delta 11B values and decreasing B/Nb ratios from the arc to the back-arc samples are attributed to the combined effects of B-isotope fractionation during progressive dehydration in the slab and a steady decrease in slab-fluid flux towards the back arc, coupled with a relatively constant degree of crustal contamination as indicated by similar Sr, Nd and Pb isotope ratios in all samples. Modelling of fluid-mineral B-isotope fractionation as a function of temperature fits the across-arc variation in delta 11B and we conclude that the B-isotope composition of arc volcanics is dominated by changing delta 11B composition of B-rich slab-fluids during progressive dehydration. Crustal contamination becomes more important towards the back-arc due to the decrease in slab-derived fluid flux. Because of this isotope fractionation effect, high delta 11B signatures in volcanic arcs need not necessarily reflect differences in the initial composition of the subducting slab. Three-component mixing calculations for slab-derived fluid, the mantle wedge and the continental crust based on B, Sr and Nd isotope data indicate that the slab-fluid component dominates the B composition of the fertile mantle and that the primary arc magmas were contaminated by an average addition of 15 to 30 % crustal material.

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Sprache(n): eng - Englisch
 Datum: 2004
 Publikationsstatus: Final veröffentlicht
 Seiten: 104 S.
 Ort, Verlag, Ausgabe: Potsdam : Deutsches GeoForschungsZentrum GFZ
 Inhaltsverzeichnis: -
 Art der Begutachtung: -
 Identifikatoren: URN: urn:nbn:de:kobv:b103-04091
 Art des Abschluß: Doktorarbeit

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Titel: Scientific Technical Report STR
Genre der Quelle: Reihe
 Urheber:
Deutsches GeoForschungsZentrum, Herausgeber              
Affiliations:
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Ort, Verlag, Ausgabe: Potsdam : Deutsches GeoForschungsZentrum
Seiten: 104 S. Band / Heft: 04/09 Artikelnummer: - Start- / Endseite: 1 - 104 Identifikator: ISSN: 1610-0956