Details
| Original language | English |
|---|---|
| Pages (from-to) | 11130-11149 |
| Number of pages | 20 |
| Journal | Journal of Geophysical Research: Solid Earth |
| Volume | 124 |
| Issue number | 11 |
| Early online date | 8 Nov 2019 |
| Publication status | Published - 27 Dec 2019 |
Abstract
The crust shows large variations in Cu isotopic composition (δ65Cu relative to NIST 976) resulting from redox reactions and other supergene processes. The significant range of δ65Cu in mantle peridotites thus could be ascribed to recycled crustal materials and/or oxidative mantle metasomatism. However, the influence of normal magmatic fractionation processes on δ65Cu variations remains poorly understood, and it is unclear whether the magmatic processes also lead to large δ65Cu variations in mantle rocks. To address the issue, we present bulk-rock δ65Cu of fresh mantle pyroxenites from the Balmuccia peridotite massif, Northern Italy. These pyroxenites formed by melt-peridotite reaction and mineral accumulation from MORB- to OIB-like, sulfide-saturated basic magmas. Mass balance calculations show that sulfide phases host >98 wt % of the Cu budget of bulk rocks (87−484 μg/g). The pyroxenites show significant variations of δ65Cu from −0.66‰ to 0.66‰, which cover the range known for peridotites, including metasomatized ones. Three subsamples from the same pyroxenite layer display >0.3‰ decrease in δ65Cu with progressive differentiation. Nevertheless, δ65Cu does not display correlations with indicators of magmatic differentiation (e.g., Mg# and Cu/Pd) for all pyroxenites in this study. This might be attributed to variable extents of magmatic sulfide segregation for different samples and/or varying δ65Cu of the pyroxenite parent magmas, which were also affected by reactive migration through peridotites. The combined processes can change δ65Cu of evolving magmas and reacted peridotites and lead to Cu isotopic heterogeneity in the mantle, without involvement of oxidative metasomatism or recycled crustal materials.
Keywords
- Cu isotopes, magmatic differentiation, mantle heterogeneity, pyroxenite, recycling, sulfide melt
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)
- Geophysics
- Earth and Planetary Sciences(all)
- Geochemistry and Petrology
- Earth and Planetary Sciences(all)
- Earth and Planetary Sciences (miscellaneous)
- Earth and Planetary Sciences(all)
- Space and Planetary Science
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In: Journal of Geophysical Research: Solid Earth, Vol. 124, No. 11, 27.12.2019, p. 11130-11149.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Copper Isotope Variations During Magmatic Migration in the Mantle
T2 - Insights From Mantle Pyroxenites in Balmuccia Peridotite Massif
AU - Zou, Zongqi
AU - Wang, Zaicong
AU - Li, Ming
AU - Becker, Harry
AU - Geng, Xianlei
AU - Hu, Zhaochu
AU - Lazarov, Marina
N1 - Funding Information: We thank Hongjin Huang, Yangtao, Zhu, Tao Luo, and Haihong Chen for their assistance in the lab. We appreciate Fang Huang and Jian Huang for the measurement of Cu isotopes at USTC, Hefei. This study was supported by National Science Foundation of China (41673027, 41722302), 111Project (BP0719022), and the MOST Special Fund from GPMR-CUG (MSFGPMR10). Many thanks go to R. Mathur and one anonymous reviewer for the constructive comments, and to Stephen Parman for editorial handling, which significantly improved this manuscript. The data for this paper are listed in Tables 1, 2, and S1–S4 and available at zenodo: https://doi.org/10.5281/zenodo.3471452.
PY - 2019/12/27
Y1 - 2019/12/27
N2 - The crust shows large variations in Cu isotopic composition (δ65Cu relative to NIST 976) resulting from redox reactions and other supergene processes. The significant range of δ65Cu in mantle peridotites thus could be ascribed to recycled crustal materials and/or oxidative mantle metasomatism. However, the influence of normal magmatic fractionation processes on δ65Cu variations remains poorly understood, and it is unclear whether the magmatic processes also lead to large δ65Cu variations in mantle rocks. To address the issue, we present bulk-rock δ65Cu of fresh mantle pyroxenites from the Balmuccia peridotite massif, Northern Italy. These pyroxenites formed by melt-peridotite reaction and mineral accumulation from MORB- to OIB-like, sulfide-saturated basic magmas. Mass balance calculations show that sulfide phases host >98 wt % of the Cu budget of bulk rocks (87−484 μg/g). The pyroxenites show significant variations of δ65Cu from −0.66‰ to 0.66‰, which cover the range known for peridotites, including metasomatized ones. Three subsamples from the same pyroxenite layer display >0.3‰ decrease in δ65Cu with progressive differentiation. Nevertheless, δ65Cu does not display correlations with indicators of magmatic differentiation (e.g., Mg# and Cu/Pd) for all pyroxenites in this study. This might be attributed to variable extents of magmatic sulfide segregation for different samples and/or varying δ65Cu of the pyroxenite parent magmas, which were also affected by reactive migration through peridotites. The combined processes can change δ65Cu of evolving magmas and reacted peridotites and lead to Cu isotopic heterogeneity in the mantle, without involvement of oxidative metasomatism or recycled crustal materials.
AB - The crust shows large variations in Cu isotopic composition (δ65Cu relative to NIST 976) resulting from redox reactions and other supergene processes. The significant range of δ65Cu in mantle peridotites thus could be ascribed to recycled crustal materials and/or oxidative mantle metasomatism. However, the influence of normal magmatic fractionation processes on δ65Cu variations remains poorly understood, and it is unclear whether the magmatic processes also lead to large δ65Cu variations in mantle rocks. To address the issue, we present bulk-rock δ65Cu of fresh mantle pyroxenites from the Balmuccia peridotite massif, Northern Italy. These pyroxenites formed by melt-peridotite reaction and mineral accumulation from MORB- to OIB-like, sulfide-saturated basic magmas. Mass balance calculations show that sulfide phases host >98 wt % of the Cu budget of bulk rocks (87−484 μg/g). The pyroxenites show significant variations of δ65Cu from −0.66‰ to 0.66‰, which cover the range known for peridotites, including metasomatized ones. Three subsamples from the same pyroxenite layer display >0.3‰ decrease in δ65Cu with progressive differentiation. Nevertheless, δ65Cu does not display correlations with indicators of magmatic differentiation (e.g., Mg# and Cu/Pd) for all pyroxenites in this study. This might be attributed to variable extents of magmatic sulfide segregation for different samples and/or varying δ65Cu of the pyroxenite parent magmas, which were also affected by reactive migration through peridotites. The combined processes can change δ65Cu of evolving magmas and reacted peridotites and lead to Cu isotopic heterogeneity in the mantle, without involvement of oxidative metasomatism or recycled crustal materials.
KW - Cu isotopes
KW - magmatic differentiation
KW - mantle heterogeneity
KW - pyroxenite
KW - recycling
KW - sulfide melt
UR - http://www.scopus.com/inward/record.url?scp=85075470583&partnerID=8YFLogxK
U2 - 10.1029/2019JB017990
DO - 10.1029/2019JB017990
M3 - Article
AN - SCOPUS:85075470583
VL - 124
SP - 11130
EP - 11149
JO - Journal of Geophysical Research: Solid Earth
JF - Journal of Geophysical Research: Solid Earth
SN - 2169-9313
IS - 11
ER -