DOI: 10.1016/j.epsl.2018.07.033
Scopus记录号: 2-s2.0-85050855730
论文题名: On the (mis)behavior of water in the mantle: Controls on nominally anhydrous mineral water content in mantle peridotites
作者: Marshall E.W. ; Lassiter J.C. ; Barnes J.D.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2018
卷: 499 起始页码: 219
结束页码: 229
语种: 英语
英文关键词: Colorado Plateau
; mantle xenoliths
; metasomatism
; nominally anhydrous minerals
; supra-subduction zone
; water
Scopus关键词: Beverages
; Hydration
; Lithology
; Mineralogy
; Robust control
; Silicate minerals
; Water
; Colorado Plateau
; Mantle xenoliths
; metasomatism
; Nominally anhydrous minerals
; Subduction zones
; Extraction
; basalt
; hydrous mineral
; mantle structure
; metasomatism
; peridotite
; subduction zone
; water content
; xenolith
; Colorado Plateau
; United States
英文摘要: In magmatic settings, water behaves as an incompatible species and should be depleted during melting and enriched during metasomatism. Previous studies have identified correlations between nominally anhydrous mineral (NAM) water content ([H2O]) and indices of metasomatism or melt extraction, seemingly confirming this behavior in the mantle. However in detail, these correlations are ambiguous and do not reflect robust controls on NAM [H2O]. We measured orthopyroxene (opx) and clinopyroxene (cpx) [H2O] in variably hydrated and metasomatized peridotite xenoliths from the Navajo volcanic field (NVF) that sample the Colorado Plateau subcontinental lithospheric mantle (SCLM), an endmember of SCLM hydration and metasomatism. These xenoliths span a wide range of pyroxene [H2O] (opx from 50 to 588 ppm wt. H2O; cpx from 38 to 581 ppm wt. H2O), but NAM [H2O] does not correlate with either indices of melt depletion or metasomatism. Growth of hydrous minerals suggests higher water activity than in anhydrous peridotites, and therefore hydrous-mineral-bearing xenoliths and anhydrous xenoliths should have different NAM [H2O] and water activities. However, when the two groups are compared no significant differences can be found in either NAM [H2O] or water activity. We propose that the high diffusivity of hydrogen in the mantle allows for equilibration of water activity in the mantle over sub-kilometer length scales over geologic time. Such diffusive equilibration reduces water activity variability and results in the blurring and destruction of correlations between NAM [H2O] and indices of metasomatism or melt extraction. As a result of diffusive equilibration of water, there is a large difference in the variability of concentration between NAM [H2O] (spanning ∼2 orders of magnitude) and similarly incompatible elements such as Ce in the same peridotites (spanning ∼4 orders of magnitude). This difference in behavior explains why H2O/Ce ratios in mantle peridotites are highly variable relative to those of basalts. © 2018 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/109706
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 Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX 78712, United States
Recommended Citation:
Marshall E.W.,Lassiter J.C.,Barnes J.D.. On the (mis)behavior of water in the mantle: Controls on nominally anhydrous mineral water content in mantle peridotites[J]. Earth and Planetary Science Letters,2018-01-01,499