DOI: 10.1016/j.epsl.2018.01.022
Scopus记录号: 2-s2.0-85044325443
论文题名: Coexistence of enriched and modern-like 142Nd signatures in Archean igneous rocks of the eastern Kaapvaal Craton, southern Africa
作者: Schneider K.P. ; Hoffmann J.E. ; Boyet M. ; Münker C. ; Kröner A.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2018
卷: 487 起始页码: 54
结束页码: 66
语种: 英语
英文关键词: 142Nd
; Ancient Gneiss Complex
; Barberton
; differentiation
; Hadean
; Kaapvaal Crato
Scopus关键词: Differentiation (calculus)
; Igneous rocks
; Lithology
; Barberton
; Gneiss complexes
; Hadean
; Kaapvaal
; ^142Nd
; Gallium
; amphibolite
; craton
; granitoid
; Hadean
; isotopic analysis
; magmatic differentiation
; neodymium isotope
; Barberton
; Kaapvaal Craton
; Mpumalanga
; South Africa
; Swaziland
英文摘要: The short-lived 146Sm–142Nd isotope system is an important tool for tracing Hadean crust–mantle differentiation processes and constraining their imprint on much younger rocks from Archean cratons. We report the first comprehensive set of high-precision 142Nd analyses for granitoids and amphibolites of the Ancient Gneiss Complex (AGC; Swaziland) and the oldest metavolcanic units of the Barberton Greenstone Belt (BGB; South Africa). The investigated samples span an age range from 3.66 Ga to 3.22 Ga and are representative of major geological units of the AGC and the lower Onverwacht Group of the BGB. Measured samples yielded μ142Nd values in the range from −8 ppm to +3 ppm relative to the JNdi-1 terrestrial standard, with typical errors smaller than 4.4 ppm. The distribution of the μ142Nd values for these 17 measured samples is bimodal with ten samples showing a tendency towards slightly negative μ142Nd anomalies, whereas seven samples have 142Nd similar to the terrestrial reference. The only confidently resolvable μ142Nd anomalies were found in a 3.44 Ga Ngwane Gneiss sample and in amphibolites of the ca. 3.45 Ga Dwalile Greenstone Remnant, revealing μ142Nd values ranging from −7.9±4.4 to −6.1±4.3 ppm. The μ142Nd deficits do not correlate with age, lithological unit, or sample locality. Instead, our results reveal that two distinct mantle domains were involved in the formation of the AGC crust. The two reservoirs can be distinguished by their μ142Nd signatures. Mantle-derived rocks tapped the enriched reservoir with negative μ142Nd at least until 3.46 Ga, whereas the granitoids preserved a negative μ142Nd signature that formed by incorporation of older AGC crust at least until 3.22 Ga. The oldest gneisses with no μ142Nd anomaly are up to 3.64 Ga in age, indicating that a modern terrestrial 142Nd reservoir was already present by early Archean times. © 2018 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/110013
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: Institut für Geologische Wissenschaften, Geochemie, Freie Universität Berlin, Malteserstraße 74-100, Berlin, 12249, Germany; Université Clermont Auvergne, CNRS, IRD, OPGC, Laboratoire Magmas et Volcans, Clermont-Ferrand, F-63000, France; Institut für Geologie und Mineralogie, Universität zu Köln, Zülpicher Straße 49b, Köln, 50674, Germany; Beijing SHRIMP Centre, Institute of Geology, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, Beijing, 100037, China; Institut für Geowissenschaften, Johannes Gutenberg-Universität Mainz, J.-J.-Becher-Weg 21, Mainz, 55128, Germany
Recommended Citation:
Schneider K.P.,Hoffmann J.E.,Boyet M.,et al. Coexistence of enriched and modern-like 142Nd signatures in Archean igneous rocks of the eastern Kaapvaal Craton, southern Africa[J]. Earth and Planetary Science Letters,2018-01-01,487