DOI: 10.1016/j.epsl.2020.116473
论文题名: The tungsten-182 record of kimberlites above the African superplume: Exploring links to the core-mantle boundary
作者: Tappe S. ; Budde G. ; Stracke A. ; Wilson A. ; Kleine T.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2020
卷: 547 语种: 英语
中文关键词: extinct radionuclides
; kimberlite origin
; LLSVP
; plate tectonics
; primordial mantle reservoirs
; ultradeep diamonds
英文关键词: Earth (planet)
; Minerals
; Seismology
; Shear flow
; Shear waves
; Structural geology
; Tungsten
; Volcanoes
; Wave propagation
; Core-mantle boundary
; Isotope abundance
; Radioactive decay
; Seismic velocities
; Shear wave velocity
; Terrestrial planets
; Thermo-chemical structures
; Ultralow velocity zone
; Volcanic rocks
; African plate
; basalt
; core-mantle boundary
; formation mechanism
; igneous geochemistry
; isotopic analysis
; isotopic composition
; kimberlite
; lava
; mantle source
; plume
; thermochemistry
; tungsten
; upper mantle
; Africa
英文摘要: Many volcanic hotspots are connected via ‘plume’ conduits to thermochemical structures with anomalously low seismic velocities at the core-mantle boundary. Basaltic lavas from some of these hotspots show anomalous daughter isotope abundances for the short-lived 129I-129Xe, 146Sm-142Nd, and 182Hf-182W radioactive decay systems, suggesting that their lower mantle sources contain material that dates back to Earth-forming events during the first 100 million years in solar system history. Survival of such ‘primordial’ remnants in Earth's mantle places important constraints on the evolution and inner workings of terrestrial planets. Here we report high-precision 182W/184W measurements for a large suite of kimberlite volcanic rocks from across the African tectonic plate, which for the past 250 million years has drifted over the most prominent thermochemical seismic anomaly at the core-mantle boundary. This so-called African LLSVP, or ‘large low shear-wave velocity province’, is widely suspected to store early Earth remnants and is implicated as the ultimate source of global Phanerozoic kimberlite magmatism. Our results show, however, that kimberlites from above the African LLSVP, including localities with lower mantle diamonds such as Letseng and Karowe Orapa A/K6, lack anomalous 182W signatures, with an average μ182W value of 0.0 ± 4.1 (2SD) for the 18 occurrences studied. If kimberlites are indeed sourced from the African LLSVP or superplume, then the extensive 182W evidence suggests that primordial or core-equilibrated mantle materials, which may contribute resolvable μ182W excesses or deficits, are only minor or locally concentrated components in the lowermost mantle, for example in the much smaller ‘ultra-low velocity zones’ or ULVZs. However, the lack of anomalous 182W may simply suggest that low-volume kimberlite magmas are not derived from hot lower mantle plumes. In this alternative scenario, kimberlite magmas originate from volatile-fluxed ambient convecting upper mantle domains beneath relatively thick and cold lithosphere from where previously ‘stranded’ lower mantle and transition zone diamonds can be plucked. © 2020 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/165304
Appears in Collections: 气候变化与战略
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作者单位: Deep & Early Earth Processes (DEEP) Research Group, Department of Geology, University of Johannesburg, P.O. Box 524, Auckland Park2006, South Africa; Institut für Planetologie, University of Münster, Wilhelm-Klemm-Strasse 10, Münster, 48149, Germany; The Isotoparium, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, 91125, United States; Institut für Mineralogie, University of Münster, Corrensstrasse 24, Münster, 48149, Germany; School of Geosciences, University of the Witwatersrand, Johannesburg, 2050, South Africa
Recommended Citation:
Tappe S.,Budde G.,Stracke A.,et al. The tungsten-182 record of kimberlites above the African superplume: Exploring links to the core-mantle boundary[J]. Earth and Planetary Science Letters,2020-01-01,547