DOI: 10.1016/j.epsl.2018.04.039
Scopus记录号: 2-s2.0-85047074974
论文题名: Controls on the iron isotopic composition of global arc magmas
作者: Foden J. ; Sossi P.A. ; Nebel O.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2018
卷: 494 起始页码: 190
结束页码: 201
语种: 英语
英文关键词: iron isotopes
; oxidation
; subduction
; thermal parameter
; volcanic arcs
Scopus关键词: Basalt
; Digital storage
; Isotopes
; Melting
; Oxidation
; Wind effects
; High oxidation state
; Iron isotopes
; Iron isotopic compositions
; Positive correlations
; Sediment contamination
; subduction
; Thermal parameters
; Volcanic arc
; Iron
; geochemistry
; iron
; isotopic composition
; isotopic fractionation
; magma chamber
; melting
; mid-ocean ridge basalt
; oxidation
; thermal regime
; volcanic arc
; Antarctica
; Banda Arc
; Indonesian seas
; Lesser Antilles
; Pacific Ocean
; Scotia Arc
; Sunda Arc
英文摘要: We determined the iron isotope composition of 130 mafic lavas from 15 arcs worldwide with the hypothesis that the results would reflect the relatively high oxidation state of arc magmas. Although this expectation was not realized, this Fe isotope data set reveals important insights into the geodynamic controls and style of the melting regimes in the sub-arc mantle. Samples are from oceanic arcs from the circum-Pacific, the Indonesian Sunda–Banda islands, Scotia and the Lesser Antilles as well as from the eastern Pacific Cascades. Their mean δ57Fe value is +0.075 ± 0.05‰ significantly lighter than MORB (+0.15 ± 0.03‰). Western Pacific arcs extend to very light δ57Fe (Kamchatka = −0.11 ± 0.04‰). This is contrary to expectation, because Fe isotope fractionation factors (Sossi et al., 2016, 2012) and the incompatibility of ferric versus ferrous iron during mantle melting, predict that melts of more oxidized sources will be enriched in heavy Fe isotopes. Subducted oxidation capacity flux may correlate with hydrous fluid release from the slab. If so, a positive correlation between each arc's thermal parameter (ϕ) and δ57Fe is predicted. On the contrary, the sampled arcs mostly contribute to a negative array with the ϕ value. High ϕ arcs, largely in the western Pacific, have primary magmas with lower δ57Fe values than the low ϕ eastern Pacific arcs. Arcs with MORB-like Sr-, Nd- and Pb-isotopes, show a large range of δ57Fe from heavy MORB-like values (Scotia or the Cascades) to very light values (Kamchatka, Tonga). Although all basalts with light δ57Fe values have MORB-like Pb-, Nd- and Sr-isotope ratios some, particularly those from eastern Indonesia, have heavier δ57Fe and higher Pb- and Sr- and lower Nd-isotope ratios reflecting sediment contamination of the mantle wedge. Because basalts with MORB-like radiogenic isotopes range all the way from heavy to light δ57Fe values this trend is process-, not source composition-driven. Neither the slab-derived influx of fluids with light iron or sediment-derived melts with heavier iron can drive the iron isotopic shifts. The trend to light iron isotopes is partly the result of repeated, hydrous flux-driven, fO2-buffered, melting of initially normal-DMM-like mantle. However the most negative δ57Fe must also reflect re-melting of sources that have experienced prior diffusive (disequilibrium) stripping of heavy Fe isotopes due to rapid melt extraction and metasomatism. Data from intra-arc to back-arc rifts in the western Pacific show that these arc signatures are rapidly dispersed by influx of DMM or OIB mantle once intra- and back-arc rifting and slab rollback gains momentum. We suggest that the characteristic light arc signatures only form when the source is lodged under arcs where sub-arc mantle undergoes corner flow forming an isolated roll. This process of heavy iron depletion is most efficient in the high ϕ arcs of the western Pacific and least prevalent in the low ϕ arcs of the eastern Pacific where δ57Fe values are MORB-like. This implies that there is a fundamental change in character of sub-arc mantle melting between east and west Pacific, percolative and fluid fluxed in the west and diapiric and decompressional in the east. © 2018 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/109858
Appears in Collections: 影响、适应和脆弱性 气候变化事实与影响
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作者单位: Department of Earth Sciences, The University of Adelaide, North Terrace, SA 5005, Australia; Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris Diderot, CNRS, Paris, F-75005, France; School of Earth, Atmosphere and Environment, Monash University, Clayton, VIC, 3084, Australia
Recommended Citation:
Foden J.,Sossi P.A.,Nebel O.. Controls on the iron isotopic composition of global arc magmas[J]. Earth and Planetary Science Letters,2018-01-01,494