Details
Original language | English |
---|---|
Article number | 107701 |
Journal | Precambrian research |
Volume | 418 |
Early online date | 27 Jan 2025 |
Publication status | E-pub ahead of print - 27 Jan 2025 |
Abstract
Banded iron formations (BIFs) are marine chemical sedimentary rocks that serve as prime archives for Precambrian paleo-environmental reconstructions. However, due to the scarcity of well-preserved Archean rocks, the aquatic environments of early Earth remain poorly constrained. In particular, fluxes derived from continents and submarine hydrothermal systems that affected Archean seawater chemistry are crucial for the understanding of the evolution of marine environments. To fill this gap, we present major- and trace element data in combination with Sm-Nd isotopes of individual BIF layers from the ca. 3.0 Ga old Murchison Greenstone Belt (MGB) of South Africa. BIF layers with low immobile element concentrations show seawater-like shale-normalized (subscript SN) rare earth and yttrium (REY SN) patterns with heavy over light REY SN enrichment and positive La SN, Eu SN, Gd SN, and Y SN anomalies, implying an anoxic marine depositional setting with contributions from high-temperature, hydrothermal systems. These BIF samples yield a Sm-Nd age of 2993 ± 97 Ma that overlaps with the proposed depositional age suggesting negligible post-depositional alteration. In contrast, BIF layers with non-seawater-like REY SN patterns yield a Sm-Nd age of 2504 ± 161 Ma, which can be linked to post-depositional alteration during the ca. 2.7 Ga Limpopo orogeny. The range of initial εNd values from −1.74 to + 0.15 in pristine BIF samples suggests that elements of mixed juvenile and evolved material from emerged continents and/or hydrothermal systems affected Murchison seawater and indicates potential oceanic water mixing in the Murchison region with water masses derived from the northern Pietersburg and the southern Kaapvaal regions.
Keywords
- BIF, Kaapvaal Craton, Mesoarchean, Murchison Greenstone Belt, REY, Seawater, Sm-Nd geochronology
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)
- Geology
- Earth and Planetary Sciences(all)
- Geochemistry and Petrology
Sustainable Development Goals
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In: Precambrian research, Vol. 418, 107701, 03.2025.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - The influence of mafic and felsic crust on the seawater chemistry ca. 3.0 billion years ago: Evidence from Nd isotopes in banded iron formations from the Murchison Greenstone Belt
AU - Krayer, Johanna Katharina
AU - Jodder, Jaganmoy
AU - Hofmann, Axel
AU - Weyer, Stefan
AU - Willbold, Matthias
AU - Schulz, Toni
AU - Koeberl, Christian
AU - Viehmann, Sebastian
PY - 2025/1/27
Y1 - 2025/1/27
N2 - Banded iron formations (BIFs) are marine chemical sedimentary rocks that serve as prime archives for Precambrian paleo-environmental reconstructions. However, due to the scarcity of well-preserved Archean rocks, the aquatic environments of early Earth remain poorly constrained. In particular, fluxes derived from continents and submarine hydrothermal systems that affected Archean seawater chemistry are crucial for the understanding of the evolution of marine environments. To fill this gap, we present major- and trace element data in combination with Sm-Nd isotopes of individual BIF layers from the ca. 3.0 Ga old Murchison Greenstone Belt (MGB) of South Africa. BIF layers with low immobile element concentrations show seawater-like shale-normalized (subscript SN) rare earth and yttrium (REY SN) patterns with heavy over light REY SN enrichment and positive La SN, Eu SN, Gd SN, and Y SN anomalies, implying an anoxic marine depositional setting with contributions from high-temperature, hydrothermal systems. These BIF samples yield a Sm-Nd age of 2993 ± 97 Ma that overlaps with the proposed depositional age suggesting negligible post-depositional alteration. In contrast, BIF layers with non-seawater-like REY SN patterns yield a Sm-Nd age of 2504 ± 161 Ma, which can be linked to post-depositional alteration during the ca. 2.7 Ga Limpopo orogeny. The range of initial εNd values from −1.74 to + 0.15 in pristine BIF samples suggests that elements of mixed juvenile and evolved material from emerged continents and/or hydrothermal systems affected Murchison seawater and indicates potential oceanic water mixing in the Murchison region with water masses derived from the northern Pietersburg and the southern Kaapvaal regions.
AB - Banded iron formations (BIFs) are marine chemical sedimentary rocks that serve as prime archives for Precambrian paleo-environmental reconstructions. However, due to the scarcity of well-preserved Archean rocks, the aquatic environments of early Earth remain poorly constrained. In particular, fluxes derived from continents and submarine hydrothermal systems that affected Archean seawater chemistry are crucial for the understanding of the evolution of marine environments. To fill this gap, we present major- and trace element data in combination with Sm-Nd isotopes of individual BIF layers from the ca. 3.0 Ga old Murchison Greenstone Belt (MGB) of South Africa. BIF layers with low immobile element concentrations show seawater-like shale-normalized (subscript SN) rare earth and yttrium (REY SN) patterns with heavy over light REY SN enrichment and positive La SN, Eu SN, Gd SN, and Y SN anomalies, implying an anoxic marine depositional setting with contributions from high-temperature, hydrothermal systems. These BIF samples yield a Sm-Nd age of 2993 ± 97 Ma that overlaps with the proposed depositional age suggesting negligible post-depositional alteration. In contrast, BIF layers with non-seawater-like REY SN patterns yield a Sm-Nd age of 2504 ± 161 Ma, which can be linked to post-depositional alteration during the ca. 2.7 Ga Limpopo orogeny. The range of initial εNd values from −1.74 to + 0.15 in pristine BIF samples suggests that elements of mixed juvenile and evolved material from emerged continents and/or hydrothermal systems affected Murchison seawater and indicates potential oceanic water mixing in the Murchison region with water masses derived from the northern Pietersburg and the southern Kaapvaal regions.
KW - BIF
KW - Kaapvaal Craton
KW - Mesoarchean
KW - Murchison Greenstone Belt
KW - REY
KW - Seawater
KW - Sm-Nd geochronology
UR - http://www.scopus.com/inward/record.url?scp=85215953611&partnerID=8YFLogxK
U2 - 10.1016/j.precamres.2025.107701
DO - 10.1016/j.precamres.2025.107701
M3 - Article
VL - 418
JO - Precambrian research
JF - Precambrian research
SN - 0301-9268
M1 - 107701
ER -