Timing of deposition and deformation of the Moodies Group (Barberton Greenstone Belt, South Africa): Very-high-resolution of Archaean surface processes

Heubeck, Christoph; Engelhardt, Jonathan; Byerly, Gary R.; Zeh, Armin; Sell, Bryan; Luber, Tim; Lowe, Donald R.

doi:10.1016/j.precamres.2013.03.021

Cited by 89 publications

(17 citation statements)

References 68 publications

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“…The Moodies Group was deposited ~3230 Ma ago (Heubeck et al. ) and is made up of three formations, each of which is a fining‐upward sequence with conglomerate or pebbly sandstone at the base; thick sandstone units in the middle; and siltstone, shale, and banded iron formations at the top, all deposited in a shallow marine to fluvial setting (Hofmann ; Brandl et al. ).…”

Section: The Barberton Greenstone Beltmentioning

confidence: 99%

Early Archean spherule layers from the Barberton Greenstone Belt, South Africa: Mineralogy and geochemistry of the spherule beds in the CT3 drill core

Ozdemir

Schulz

Koeberl

et al. 2017

Meteorit & Planetary Scien

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Abstract-Little is known about the Hadean and the Archean impact record on Earth. In the CT3 drill core from the Fig Tree Group of the northern Barberton Greenstone Belt, 17 spherule layer intersections occur, which, provide an outstanding new opportunity to gain insights into meteorite bombardment of the early Earth. CT3 spherules, as primary features, mostly exhibit textural patterns similar to those of the other Barberton spherule layers, but locally mineralogical and chemical compositional differences are observed, likely as a result of various degrees of alteration. The observed mineralogy of the spherule layers is of secondary origin and comprises K-feldspar, phyllosilicates, carbonates, sulfides, and oxides, with the exception of secondary Ni-Cr spinel that is of primary origin. Our petrographic investigations suggest alteration by K-metasomatism, sericitization, silicification, and carbonatization. Siderophile element contents of bulk samples show significant enrichments in Ni (up to 2 wt%) and Ir (up to~3 ppm), similar to previously studied Archean spherule layers. These values are indicative of the presence of a meteoritic component. On the other hand, lithophile and chalcophile element abundances indicate hydrothermal overprint on the CT3 samples; this may also have influenced the redistribution of the meteoritic component(s). Last, we group the CT3 spherule layers, which occur in three intervals (A, B, and C), according to their petrographic and geochemical features, which indicate evidence for at least three distinct impact events before tectonic overprint that affected the original deposits.

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Section: The Barberton Greenstone Beltmentioning

confidence: 99%

Early Archean spherule layers from the Barberton Greenstone Belt, South Africa: Mineralogy and geochemistry of the spherule beds in the CT3 drill core

Ozdemir

Schulz

Koeberl

et al. 2017

Meteorit & Planetary Scien

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“…3.4 Ga old Pilbara Craton was reorganized via gravitation overturns, allowing felsic continental crust to reach the uppermost continental levels and be available for subaerial weathering and erosion processes. Because Hf-Nd isotope decoupling was observed in BIFs at two near-contemporaneous localities [8,9], Hf-Nd decoupling can be considered rather as a global than a local phenomenon in Late Archean oceans [9] and it is now important to further step back in time and pinpoint the timing of which more evolved continental crust had impact on the local, but also global seawater chemistry, because Palaeo-to Mesoarchean greenstone belt succession contain rare siliciclastic intercalations that give sedimentological and geochemical evidence for weathered and eroded evolved continental material [10][11][12]. For instance, a small data set of decoupled Hf and Nd isotopes are reported in marine chemical sediments from the 3.4 Ga old Barberton [69] and 3.7 Ga old Isua Greenstone Belts [71], indicating that incongruent Hf weathering of more evolved material potentially already had impact on local ancient seawater already during the Palaeo-and Eoarchean.…”

Section: Implications For the Geodynamical Evolution Of Archaean Contmentioning

confidence: 99%

“…These findings in combination have major implications on the geodynamical evolution of the Archean continents and, of course, on the nutrient flux derived from the continents into the earliest marine habitats on Earth. However, clastic sediments in worldwide-distributed greenstone belt successions, e.g., [10][11][12], indicate that at least parts of more evolved continental crust were already subaerial weathered and eroded during the Meso-and Paleoarchean, potentially uplifted by gravitational overturn of felsic proto-crust [13]. The urgent scientific questions remain to which amount and when evolved continental crust was available for chemical weathering and erosion processes to affect Archean seawater chemistry and the coincident flux of (bio)available nutrients into the earliest marine habitats on Earth.…”

Section: Introductionmentioning

confidence: 99%

Hf-Nd Isotopes in Archean Marine Chemical Sediments: Implications for the Geodynamical History of Early Earth and Its Impact on Earliest Marine Habitats

Viehmann

2018

Geosciences

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Abstract:The Hf-Nd isotope systems are coupled in magmatic systems, but incongruent Hf weathering ('zircon effect') of the continental crust leads to a decoupling of the Hf-Nd isotope systems in low-temperature environments during weathering and erosion processes. The Hf-Nd isotope record was recently dated back from the Cenozoic oceans until the Archean, showing that both isotope systems were already decoupled in seawater 2.7 Ga ago and potentially 3.4 Ga and 3.7 Ga ago. While there might have existed a hydrothermal pathway for Hf into Archean seawater, incongruent Hf weathering of more evolved, zircon-bearing uppermost continental crust that was emerged and available for subaerial weathering accounts for a significant decoupling of Hf-Nd isotopes in the dissolved (<0.2 µm) and suspended (>0.2 µm) fractions of Early Earth's seawater. These findings contradict the consensus that uppermost Archean continental crust was (ultra)mafic in composition and predominantly submerged. Hence, Hf-Nd isotopes in Archean marine chemical sediments provide the unique potential for future research to trace the emergence of evolved continental crust, which in turn has major implications for the geodynamical evolution of Early Earth and the nutrient flux into the earliest marine habitats on Earth.

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“…This group is mainly composed of medium-to-coarse-grained sandstone [4,5]. Heubeck et al (2013) estimated that the Moodies Group accumulated rapidly at rates of ca. 0.1 to 1 mm / year within <1 to 14 Ma using zircon U-Pb isochrones [6].…”

Section: Introductionmentioning

confidence: 99%

“…Heubeck et al (2013) estimated that the Moodies Group accumulated rapidly at rates of ca. 0.1 to 1 mm / year within <1 to 14 Ma using zircon U-Pb isochrones [6]. The quartz-rich siliciclastic sands, conglomerates, and silts accumulated on terrestrial to shallow-marine settings, reflecting alluvial, coastal flood plain and intertidal to subtidal depositional environments [5].…”

Section: Introductionmentioning

confidence: 99%

Multiple Sulfur Isotope Records of the 3.22 Ga Moodies Group, Barberton Greenstone Belt

et al. 2020

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The Moodies Group, the uppermost unit in the Barberton Greenstone Belt (BGB) in South Africa, is a ~3.7-km-thick coarse clastic succession accumulated on terrestrial-to-shallow marine settings at around 3.22 Ga. The multiple sulfur isotopic composition of pyrite of Moodies intervals was newly obtained to examine the influence of these depositional settings on the sulfur isotope record. Conglomerate and sandstone rocks were collected from three synclines north of the Inyoka Fault of the central BGB, namely, the Eureka, Dycedale, and Saddleback synclines. The sulfur isotopic composition of pyrite was analyzed by Secondary Ion Mass Spectrometry (SIMS) for 6 samples from the three synclines and by Isotope Ratio Mass Spectrometry (IR-MS) for 17 samples from a stratigraphic section in the Saddleback Syncline. The present results show a signal of mass-independent fractionation of sulfur isotopes (S-MIF), although t-tests statistically demonstrated that the Moodies S-MIF signals (mostly 0‰ < ∆33S < +0.5‰) are significantly small compared to the signal of the older Paleoarchean (3.6–3.2 Ga) records. These peculiar signatures might be related to initial deposition of detrital pyrite of juvenile origin from the surrounding intrusive (tonalite–trondhjemite–granodiorite; TTG) and felsic volcanic rocks, and/or to secondary addition of hydrothermal sulfur during late metasomatism. Moreover, fast accumulation (~0.1–1 mm/year) of the Moodies sediments might have led to a reduced accumulation of sulfur derived from an atmospheric source during their deposition. As a result, the sulfur isotopic composition of the sediments may have become susceptible to the secondary addition of metasomatic sulfur on a mass balance point of view. The sulfur isotopic composition of Moodies pyrite is similar to the composition of sulfides from nearby gold mines. It suggests that, after the Moodies deposition, metasomatic pyrite formation commonly occurred north of the Inyoka Fault in the central BGB at 3.1–3.0 Ga.

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Timing of deposition and deformation of the Moodies Group (Barberton Greenstone Belt, South Africa): Very-high-resolution of Archaean surface processes

Cited by 89 publications

References 68 publications

Early Archean spherule layers from the Barberton Greenstone Belt, South Africa: Mineralogy and geochemistry of the spherule beds in the CT3 drill core

Early Archean spherule layers from the Barberton Greenstone Belt, South Africa: Mineralogy and geochemistry of the spherule beds in the CT3 drill core

Hf-Nd Isotopes in Archean Marine Chemical Sediments: Implications for the Geodynamical History of Early Earth and Its Impact on Earliest Marine Habitats

Multiple Sulfur Isotope Records of the 3.22 Ga Moodies Group, Barberton Greenstone Belt

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