DOI: 10.1016/j.epsl.2018.06.044
Scopus记录号: 2-s2.0-85050001050
论文题名: Plate tectonic cycling modulates Earth's 3He/22Ne ratio
作者: Dygert N. ; Jackson C.R.M. ; Hesse M.A. ; Tremblay M.M. ; Shuster D.L. ; Gu J.T.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2018
卷: 498 起始页码: 309
结束页码: 321
语种: 英语
英文关键词: 3He/22Ne
; diffusion
; dunite channel
; kinetic fractionation
; mantle lithosphere
; noble gas
Scopus关键词: Basalt
; Diffusion
; Helium
; Inert gases
; Mixing
; Neon
; Submarine geology
; Tectonics
; dunite channel
; Kinetic fractionations
; Mantle lithosphere
; Mantle upwellings
; Mid ocean ridge basalts
; Ocean island basalts
; Orders of magnitude
; ^3He/^22Ne
; Structural geology
; diffusion
; dunite
; fractionation
; helium
; isotopic ratio
; lithospheric structure
; mantle structure
; neon
; plate tectonics
; reaction kinetics
英文摘要: The ratio of 3He and 22Ne varies throughout the mantle. This observation is surprising because 3He and 22Ne are not produced in the mantle, are highly incompatible during mantle melting, and are not recycled back into the mantle by subduction of oceanic sediment or basaltic crust. Our new compilation yields average 3He/22Ne ratios of 7.5 ± 1.2 and 3.5 ± 2.4 for mid-ocean ridge basalt (MORB) mantle and ocean island basalt (OIB) mantle sources respectively. The low 3He/22Ne of OIB mantle approaches planetary precursor 3He/22Ne values; ∼1 for chondrites and ∼1.5 for the solar nebula. The high 3He/22Ne of the MORB mantle is not similar to any planetary precursor, requiring a mechanism for fractionating He from Ne in the mantle and suggesting isolation of distinct mantle reservoirs throughout geologic time. New experimental results reported here demonstrate that He and Ne diffuse at rates differing by one or more orders of magnitude at relevant temperatures in mantle materials. We model the formation of a MORB mantle with an elevated 3He/22Ne ratio through kinetically modulated chemical exchange between dunite channel-hosted basaltic liquids and harzburgite wallrock beneath mid-ocean ridges. Over timescales relevant to mantle upwelling beneath spreading centers, He may diffuse tens to hundreds of meters into wallrock while Ne is effectively immobile, producing a mantle lithosphere regassed with respect to He and depleted with respect to Ne, with a net elevated 3He/22Ne. Subduction of high 3He/22Ne mantle lithosphere throughout geologic time would generate a MORB source with high 3He/22Ne. Mixing models suggest that to preserve a high 3He/22Ne reservoir, MORB mantle mixing timescales must be on the order of hundreds of millions of years or longer, that mantle convection has not been layered about the transition zone for most of geologic time, and that Earth's convecting mantle has lost at least 96% of its primordial volatile elements. The most depleted, highest 3He/22Ne mantle may be best preserved in the lower mantle where relatively high viscosities impede mechanical mixing. © 2018 Elsevier B.V.
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资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/109759
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; Planetary Geosciences Institute, Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, Knoxville, TN 37996, United States; Geophysical Laboratory, Carnegie Institution for Science, Washington, DC 20015, United States; National Museum of Natural History, Smithsonian Institution, Washington, DC 20560, United States; Department of Earth and Planetary Science, University of California, Berkeley, Berkeley, CA 94720, United States; Berkeley Geochronology Center, Berkeley, CA 94709, United States; Scottish Universities Environmental Research Centre, East Kilbride, Scotland G75 0QF, United Kingdom
Recommended Citation:
Dygert N.,Jackson C.R.M.,Hesse M.A.,et al. Plate tectonic cycling modulates Earth's 3He/22Ne ratio[J]. Earth and Planetary Science Letters,2018-01-01,498