Boron isotope fractionation in magma via crustal carbonate dissolution
2016 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, 30774Article in journal (Refereed) Published
Carbon dioxide released by arc volcanoes is widely considered to originate from the mantle and from subducted sediments. Fluids released from upper arc carbonates, however, have recently been proposed to help modulate arc CO2 fluxes. Here we use boron as a tracer, which substitutes for carbon in limestone, to further investigate crustal carbonate degassing in volcanic arcs. We performed laboratory experiments replicating limestone assimilation into magma at crustal pressure-temperature conditions and analysed boron isotope ratios in the resulting experimental glasses. Limestone dissolution and assimilation generates CaO-enriched glass near the reaction site and a CO2-dominated vapour phase. The CaO-rich glasses have extremely low delta B-11 values down to -41.5%, reflecting preferential partitioning of B-10 into the assimilating melt. Loss of B-11 from the reaction site occurs via the CO2 vapour phase generated during carbonate dissolution, which transports B-11 away from the reaction site as a boron-rich fluid phase. Our results demonstrate the efficacy of boron isotope fractionation during crustal carbonate assimilation and suggest that low delta B-11 melt values in arc magmas could flag shallow-level additions to the subduction cycle.
Place, publisher, year, edition, pages
2016. Vol. 6, 30774
Earth and Related Environmental Sciences
IdentifiersURN: urn:nbn:se:uu:diva-302679DOI: 10.1038/srep30774ISI: 000380873400001PubMedID: 27488228OAI: oai:DiVA.org:uu-302679DiVA: diva2:967425
FunderSwedish Research CouncilThe Royal Swedish Academy of SciencesNatural‐Disaster Science