Disentangling the Roles of Subducted Volatile Contributions and Mantle Source Heterogeneity in the Production of Magmas Beneath the Washington Cascades

IF 2.9 2区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS
K. J. Walowski, P. J. Wallace, S. M. DeBari, I. Wada, S. D. Shaw, J. Rea
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引用次数: 0

Abstract

The compositional diversity of primitive arc basalts has long inspired questions regarding the drivers of magmatism in subduction zones, including the roles of decompression melting, mantle heterogeneity, and the amount and composition of slab-derived materials. This contribution presents the volatile (H2O, Cl, and S), major, and trace element compositions of melt inclusions from basaltic magmas erupted at three volcanic centers in the Washington Cascades: Mount St. Helens (two basaltic tephras, 2.0–1.7 ka), Indian Heaven Volcanic Field (two <600 ka basaltic hyaloclastite tuffs), and Glacier Peak (late Pleistocene to Holocene basaltic tephra from Whitechuck and Indian Pass cones). Compositions corrected to be in equilibrium with mantle olivine display variability in Nb and trace element ratios indicative of mantle source variability that impressively spans nearly the entire range of arc magmas globally. All volcanic centers have magmas with H2O and Cl contributions from the downgoing plate that overlap with other Cascade Arc segments. Volatile abundances and trace element ratios support a model of melting of a highly variably mantle wedge driven by a subduction component of variably saline fluid and/or slab partial melt. Magmas from Glacier Peak in northern Washington have unusually high Th/Yb ratios that are similar to Lassen region basalts, indicating possible contributions of “subcreted” metasediments that geophysical data suggest are not present beneath central Oregon and southern Washington. This data set adds to the growing inventory of primitive magma volatile concentrations and provides insight into spatial distributions of mantle heterogeneity and the role of slab components in the petrogenesis of arc magmas.

Abstract Image

厘清俯冲挥发物贡献和地幔源异质性在华盛顿喀斯喀特山脉下岩浆生成中的作用
原始弧玄武岩成分的多样性长期以来一直激发着有关俯冲带岩浆活动驱动因素的问题,包括减压熔融的作用、地幔异质性以及板块衍生物质的数量和成分。本文介绍了华盛顿喀斯喀特山脉三个火山中心喷发的玄武岩浆中熔融包裹体的挥发物(H2O、Cl 和 S)、主要元素和痕量元素组成:圣海伦火山(两块玄武岩凝灰岩,2.0-1.7 ka)、印第安天堂火山场(两块 <600 ka 玄武玄武岩凝灰岩)和冰川峰(来自怀特查克和印第安帕斯火山锥的晚更新世至全新世玄武岩凝灰岩)。被校正为与地幔橄榄石平衡的成分显示出铌和痕量元素比率的变化,表明地幔源的变化几乎横跨全球弧形岩浆的整个范围,令人印象深刻。所有火山中心的岩浆都含有来自下行板块的 H2O 和 Cl,这些岩浆与其他级联弧段重叠。挥发物丰度和痕量元素比率支持由不同盐分流体和/或板块部分熔体的俯冲成分驱动的高变化地幔楔熔化模型。华盛顿州北部冰川峰的岩浆具有与拉森地区玄武岩相似的异常高的Th/Yb比率,这表明可能有 "俯冲 "元古界的参与,而地球物理数据表明俄勒冈州中部和华盛顿州南部地下并不存在这种元古界。这组数据增加了原始岩浆挥发物浓度的库存量,并为了解地幔异质性的空间分布和板块成分在弧岩浆成岩过程中的作用提供了信息。
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来源期刊
Geochemistry Geophysics Geosystems
Geochemistry Geophysics Geosystems 地学-地球化学与地球物理
CiteScore
5.90
自引率
11.40%
发文量
252
审稿时长
1 months
期刊介绍: Geochemistry, Geophysics, Geosystems (G3) publishes research papers on Earth and planetary processes with a focus on understanding the Earth as a system. Observational, experimental, and theoretical investigations of the solid Earth, hydrosphere, atmosphere, biosphere, and solar system at all spatial and temporal scales are welcome. Articles should be of broad interest, and interdisciplinary approaches are encouraged. Areas of interest for this peer-reviewed journal include, but are not limited to: The physics and chemistry of the Earth, including its structure, composition, physical properties, dynamics, and evolution Principles and applications of geochemical proxies to studies of Earth history The physical properties, composition, and temporal evolution of the Earth''s major reservoirs and the coupling between them The dynamics of geochemical and biogeochemical cycles at all spatial and temporal scales Physical and cosmochemical constraints on the composition, origin, and evolution of the Earth and other terrestrial planets The chemistry and physics of solar system materials that are relevant to the formation, evolution, and current state of the Earth and the planets Advances in modeling, observation, and experimentation that are of widespread interest in the geosciences.
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