DOI: 10.1016/j.epsl.2020.116251
论文题名: Europium and barium enrichments in compositionally zoned felsic tuffs: A smoking gun for the origin of chemical and physical gradients by cumulate melting
作者: Wolff J.A. ; Forni F. ; Ellis B.S. ; Szymanowski D.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2020
卷: 540 语种: 英语
中文关键词: compositional zoning
; crystal mush
; cumulate melting
; Eu anomalies
; felsic magmas
; mafic recharge
英文关键词: Alumina
; Aluminum oxide
; Barium
; Barium alloys
; Binary alloys
; Crystallinity
; Crystals
; Deposits
; Endocrinology
; Feldspar
; Glass
; Melting
; Silica
; Volcanic rocks
; Volcanoes
; Zoning
; Compositional zoning
; Element partitioning
; Eu anomalies
; Felsic magma
; mafic recharge
; Pyroclastic deposits
; Supernatant liquids
; Thermal rejuvenation
; Europium
; barium
; crystallization
; europium
; felsic rock
; partial melting
; physicochemical property
; pyroclastic deposit
; tuff
; zoning
英文摘要: Felsic pyroclastic deposits of overall low crystallinity erupted from caldera volcanoes frequently display internal gradients in composition and crystal content. The chemical gradients in the melt phase are consistent with differentiation paths and mineral/melt element partitioning predicted from the observed phenocryst assemblage. The same units typically show crystal-scale evidence for generation of eruptible magma by thermal rejuvenation of initially static, high-crystallinity (>50%) mush. Deposit-scale zoning can be reconciled with system rejuvenation by a model in which a high-crystallinity cumulate mush beneath its cognate supernatant liquid is melted by more mafic recharge to produce denser, remobilized magma of accumulative composition. In this model, zoning is a symptom of thermal rejuvenation, but requires a fusible cumulate, as provided by alkali feldspar-rich assemblages. We review existing data and present new whole-rock, glass and mineral compositions for nine examples of zoned felsic units, across the spectrum of alumina- and silica-saturation. We show that whole rocks and glasses in the late-erupted or least-evolved parts of these examples are strongly enriched in Ba (and, less consistently, Sr), and exhibit positive Eu anomalies, providing unequivocal evidence for the production of eruptible magma through melting of alkali feldspar cumulate mush. Hence, felsic volcanic rocks of low to moderate crystallinity may nonetheless have chemical signatures characteristic of cumulates. However, many other zoned tuffs show more subdued Ba-Eu enrichment and lack positive Eu anomalies. Enrichment of Eu and Ba in the melt is modulated by the extent and degree of equilibration during melting, and may be a transient signal that is quickly suppressed by new feldspar growth occurring between melting and eruption. In cases of very highly evolved rhyolites, the prior depletion of Ba, Sr and Eu by extensive alkali feldspar fractionation precludes development of any strong enrichment, although the patterns of relative variation are similar to those in the examples discussed here. © 2020 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/165349
Appears in Collections: 气候变化与战略
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作者单位: School of the Environment, Washington State University, Pullman, WA 99164, United States; Asian School of the Environment, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore; Institute of Geochemistry and Petrology, ETH Zürich, NW Clausiusstrasse 25, Zürich, 8092, Switzerland; Department of Geosciences, Princeton University, Guyot Hall, Princeton, NJ 08544, United States
Recommended Citation:
Wolff J.A.,Forni F.,Ellis B.S.,et al. Europium and barium enrichments in compositionally zoned felsic tuffs: A smoking gun for the origin of chemical and physical gradients by cumulate melting[J]. Earth and Planetary Science Letters,2020-01-01,540