Formation mechanisms of macroscopic globules in andesitic glasses from the Izu–Bonin–Mariana forearc (IODP Expedition 352)

Medientyp: E-Artikel

Titel: Formation mechanisms of macroscopic globules in andesitic glasses from the Izu–Bonin–Mariana forearc (IODP Expedition 352)

Beteiligte: Fonseca, Raúl O. C. [VerfasserIn]; Michely, Lina T. [VerfasserIn]; Kirchenbaur, Maria [VerfasserIn]; Prytulak, Julie [VerfasserIn]; Ryan, Jeffrey [VerfasserIn]; Hauke, Kerstin [VerfasserIn]; Leitzke, Felipe P. [VerfasserIn]; Almeev, Renat R. [VerfasserIn]; Marien, Chris S. [VerfasserIn]; Gerdes, Axel [VerfasserIn]; Schellhorn, Rico [VerfasserIn]; Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum, Bochum, Germany [VerfasserIn]; Agroislab GmbH, Jülich, Germany [VerfasserIn]; Institut für Mineralogie, Leibniz Universität Hannover, Hannover, Germany [VerfasserIn]; Science Labs, Department of Earth Sciences, Durham University, Durham, UK [VerfasserIn]; School of Geosciences, University of South Florida, Tampa, USA [VerfasserIn]; Institut für Geowissenschaften, Universität Bonn, Bonn, Germany [VerfasserIn]; Laboratório de Geologia Isotópica, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brasil [VerfasserIn]; Institut für Geologie und Mineralogie, Universität zu Köln, Köln, Germany [VerfasserIn]; Institut für Geowissenschaften - Frankfurt Isotope and Element Research Center (FIERCE), Goethe Universität Frankfurt, Frankfurt am Main, Germany [VerfasserIn]

Erschienen: Springer Berlin Heidelberg, 2020-12-23

Sprache: Englisch

DOI: https://doi.org/10.1007/s00410-020-01756-3

Schlagwörter: Liquid immiscibility ; Globular textures ; B and Sr isotopes ; Andesites ; Izu-Bonin forearc

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Beschreibung: The Izu–Bonin–Mariana volcanic arc is situated at a convergent plate margin where subduction initiation triggered the formation of MORB-like forearc basalts as a result of decompression melting and near-trench spreading. International Ocean Discovery Program (IODP) Expedition 352 recovered samples within the forearc basalt stratigraphy that contained unusual macroscopic globular textures hosted in andesitic glass (Unit 6, Hole 1440B). It is unclear how these andesites, which are unique in a stratigraphic sequence dominated by forearc basalts, and the globular textures therein may have formed. Here, we present detailed textural evidence, major and trace element analysis, as well as B and Sr isotope compositions, to inves tigate the genesis of these globular andesites. Samples consist of K2 O-rich basaltic globules set in a glassy groundmass of andesitic composition. Between these two textural domains a likely hydrated interface of devitrified glass occurs, which, based on textural evidence, seems to be genetically linked to the formation of the globules. The andesitic groundmass is Cl rich (ca. 3000 𝜇g/g), whereas globules and the interface are Cl poor (ca. 300 𝜇g/g). Concentrations of fluid-mobile trace elements also appear to be fractionated in that globules and show enrichments in B, K, Rb, Cs, and Tl, but not in Ba and W relative to the andesitic groundmass, whereas the interface shows depletions in the latter, but is enriched in the former. Interestingly, globules and andesitic groundmass have identical Sr isotopic composition within analytical uncertainty (87 Sr∕86 Sr of 0.70580 ± 10), indicating that they likely formed from the same source. However, globules show high 𝛿11B (ca. + 7‰), whereas their host andesites are isotopically lighter (ca. – 1 ‰), potentially indicating that whatever process led to their formation either introduced heavier B isotopes to the globules, or induced stable isotope fractionation of B between globules and their groundmass. Based on the bulk of the textural information and ...

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