DOI: 10.1016/j.epsl.2018.02.004
Scopus记录号: 2-s2.0-85044782790
论文题名: Enstatite chondrites EL3 as building blocks for the Earth: The debate over the 146Sm–142Nd systematics
作者: Boyet M. ; Bouvier A. ; Frossard P. ; Hammouda T. ; Garçon M. ; Gannoun A.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2018
卷: 488 起始页码: 68
结束页码: 78
语种: 英语
英文关键词: 146Sm–142Nd systematics
; Earth's building blocks
; Earth's evolution
; enstatite chondrites
Scopus关键词: Calcium compounds
; Heterojunctions
; Isotopes
; Mass spectrometry
; Meteorites
; Minerals
; Neodymium
; Rare earths
; Silicates
; Building blockes
; Chondrite meteorites
; enstatite chondrites
; Incompatible element
; Isotopic measurement
; Spectrometry technique
; Stable isotope ratios
; Thermal metamorphism
; Sulfur compounds
; enstatite chondrite
; isotopic composition
; isotopic ratio
; neodymium isotope
; planetary evolution
; samarium
; stable isotope
; Sitta
英文摘要: The 146Sm–142Nd extinct decay scheme (146Sm half-life of 103 My) is a powerful tool to trace early Earth silicate differentiation. Differences in 142Nd abundance measured between different chondrite meteorite groups and the modern Earth challenges the interpretation of the 142Nd isotopic variations found in terrestrial samples because the origin of the Earth and the nature of its building blocks is still an ongoing debate. As bulk meteorites, the enstatite chondrites (EC) have isotope signatures that are the closest to the Earth value with an average small deficit of ∼10 ppm in 142Nd relative to modern terrestrial samples. Here we review all the Nd isotope data measured on EC so far, and present the first measurements on an observed meteorite fall Almahata Sitta containing pristine fragments of an unmetamorphosed enstatite chondrite belonging to the EL3 subgroup. Once 142Nd/144Nd ratios are normalized to a common chondritic evolution, samples from the EC group (both EL and EH) have a deficit in 142Nd but the dispersion is important (μ142Nd=−10±12 (2SD) ppm). This scatter reflects their unique mineralogy associated to their formation in reduced conditions (low fO2 or high C/O). Rare-earth elements are mainly carried by the sulfide phase oldhamite (CaS) that is more easily altered than silicates by weathering since most of the EC meteorites are desert finds. The EL6 have fractionated rare-earth element patterns with depletion in the most incompatible elements. Deviations in Nd mass independent stable isotope ratios in enstatite chondrites relative to terrestrial standard are not resolved with the level of analytical precision achieved by modern mass spectrometry techniques. Here we show that enstatite chondrites from the EL3 and EL6 subgroups may come from different parent bodies. Samples from the EL3 subgroup have Nd (μ142Nd=−0.8±7.0, 2SD) and Ru isotope ratios undistinguishable from that of the Bulk Silicate Earth. EL3 samples have never been analyzed for Mo isotopes. Because these enstatite chondrites are relatively small in size and number, they are usually not available for destructive isotopic measurements. Average values based on the measurement of EL6 samples should not be considered as representative of the whole EL group because of melting and thermal metamorphism events affecting the Sm/Nd ratios and prolonged open-system history. The EL3 chondrites are the best candidates as the Earth's building blocks. These new results remove the need to change the composition of refractory incompatible elements early in Earth's history. © 2018 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/109994
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: Laboratoire Magmas et Volcans, Université Clermont Auvergne, France; Department of Earth Sciences, Centre for Planetary Science and Exploration, University of Western Ontario, London, Canada; Department of Earth Sciences, ETH Zurich, Switzerland
Recommended Citation:
Boyet M.,Bouvier A.,Frossard P.,et al. Enstatite chondrites EL3 as building blocks for the Earth: The debate over the 146Sm–142Nd systematics[J]. Earth and Planetary Science Letters,2018-01-01,488