Further Rb-Sr age and isotope data on Early and Late Archaean rocks from the Rhodesian craton

Moorbath, S.; Wilson, J. F.; Goodwin, Roy; Humm, M. J.

doi:10.1016/0301-9268(77)90030-4

Cited by 41 publications

(13 citation statements)

References 8 publications

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“…Horstwood et al 1999). Gneisses from the Tokwe segment have Sm-Nd T DM ages between 3.65 and 3.51 Ga (Horstwood et al, 1999;Taylor et al, 1991) and low initial Sr ratios (0.700-0.701; Hawkesworth et al, 1975;Moorbath et al, 1977), suggesting that they were derived from depleted or chondritic mantle sources. Numerous infolded greenstone remnants (several kilometres long) have been assigned to the undated Sebakwian Group.…”

Section: Geology Of the Zimbabwe Cratonmentioning

confidence: 99%

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Juvenile crust formation in the Zimbabwe Craton deduced from the O-Hf isotopic record of 3.8–3.1 Ga detrital zircons

Bolhar

Hofmann

Kemp

et al. 2017

Geochimica et Cosmochimica Acta

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Section: Geology Of the Zimbabwe Cratonmentioning

confidence: 99%

“…The protracted cratonic history was already beginning to emerge from whole rock Pb isotope studies of intrusive suites in Zimbabwe, in which high U/Pb sources were postulated to have been remobilized since Palaeoarchaean times (e.g. Moorbath et al, 1977;Taylor et al, 1991;.…”

Section: Introductionmentioning

confidence: 99%

Juvenile crust formation in the Zimbabwe Craton deduced from the O-Hf isotopic record of 3.8–3.1 Ga detrital zircons

Bolhar

Hofmann

Kemp

et al. 2017

Geochimica et Cosmochimica Acta

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“…The oldest rocks intruded at ϳ3.6 Ga and are exposed in the Shabani-Mashaba area north of the Belingwe Greenstone Belt (Hawkesworth et al, 1975;Moorbath et al, 1977b). The selected TTG are mostly tonalitic banded gneisses characterised by low Rb concentrations and only slightly evolved Sr isotopic compositions ( 87 Sr/ 86 Sr i ϳ 0.700) as well as Nd values of around 0.8 (Moorbath et al, 1976(Moorbath et al, , 1977b.…”

Section: Samplesmentioning

confidence: 99%

“…Samples from the Zimbabwe Craton consist of four TTG gneisses from the Shabani-Mashaba area (Table 1). Most samples have been previously investigated for geochemistry and several isotope systems (Rb-Sr, Th-U-Pb, Sm-Nd; Re-Os, e.g., Black et al, 1971;Moorbath et al, 1972Moorbath et al, , 1973Moorbath et al, , 1975Moorbath et al, , 1976Moorbath et al, , 1977aMoorbath et al, , 1977bMoorbath et al, , 1986Baadsgaard, 1973;Hawkesworth et al, 1975;Taylor et al, 1984Taylor et al, , 1991Baadsgaard et al, 1986aBaadsgaard et al, , 1986bBennett et al, 1993;Luais and Hawkesworth, 1994;Whitehouse et al, 1999;Frei et al, 1999Frei et al, , 2002Frei et al, , 2004Kamber, 2002, 2003;Frei and Jensen, 2003).…”

Section: Samplesmentioning

confidence: 99%

Ca isotope fingerprints of early crust-mantle evolution

Kreissig

Elliott

2005

Geochimica et Cosmochimica Acta

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Ca ratios indistinguishable from our measured modern MORB value (i.e., Ca (3.6) ϳ 0). Greenland samples, however, are very diverse ranging from Ca (3.7) ϭ 0.1 in mafic pillow lavas and felsic sheets from the Isua supracrustal belt, up to very radiogenic signatures ( Ca (3.7) ϭ 2.9) in both mafic rocks of the Akilia association and felsic TTG from the coastal Amîtsoq gneisses.At face value, these results imply the Zimbabwe crust is juvenile whereas most Greenland samples include an earlier crustal component. Yet the west Greenland craton, as with many Archaean localities, has experienced a complex geological history and the interpretation of age-corrected initial isotope values requires great care. Both felsic and mafic samples from Greenland display Ca (3.7) so radiogenic that they are not readily explained by crustal growth scenarios. The presence of such radiogenic 40 Ca/ 44 Ca found in low K/Ca plagioclases requires Ca isotope exchange between plagioclase and whole rock during later metamorphic event(s). In addition the unexpectedly radiogenic Ca isotope ratios in some mafic samples reflect anomalous K/Ca ratios as a result of intense K-metasomatism ϳ3.6 Ga. Thus Ca isotope measurements are not a robust tracer of crustal growth in the presence of intense tectono-metamorphic processes. Coupled with other isotope data, however, the degree of overprint can be estimated and the 40 Ca/ 44 Ca ratio of a little disturbed sample hints at a small contribution of Hadean protocrust in the coastal part of the Godthåbsfjord area (Southwest Greenland). In the majority of Zimbabwe TTG samples, unradiogenic initial Ca isotope ratios point to very little prior crustal history and minor subsequent disturbance. We thus infer that the modest initial Nd ϳ0.8 of the Zimbabwean samples is representative of the depleted mantle at ϳ3.6 Ga. Furthermore, Ca isotope systematics provide little support for a "steady state" model of crustal growth.

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“…The IRupemba stromatolites are contiguous domical structures and are generally accepted as algal/bacterial structures (4), i.e., they are not pseudostromatolites formed solely by inorganic processes. Their age, derived through stratigraphic correlations from isotopically dated igneous events, is t2.7 X 109 years (4)(5)(6). The Rupemba-Belingwe stromatolites seem to correspond stratigraphically to the Bulawayan (Huntsman Quarry) stromatolites (7).…”

mentioning

confidence: 99%

2,5-Dimethylfuran from ≈2.7 × 10 ⁹ -year-old Rupemba—Belingwe stromatolite, Rhodesia: Potential evidence for remnants of carbohydrates

Sklarew¹,

Nagy²

1979

Proc. Natl. Acad. Sci. U.S.A.

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2,5-Dimethylfuran, 2-methylfuran, and C9-C20 n-alkanes have been isolated from the kerogen of a Rupemba stromatolite. These furans could be the oldest known stable remnants of biological carbohydrates if it is possible to prove that their progenitors are as old as the rock. Experiments showed that it is improbable that these compounds are analytical artifacts or laboratory contaminations. Postdepositional contaminations caused by fluids flowing through the rocks seem doubtful because of minimal permeability, which is supported by petrographic observations. Contamination by diffusion also appears to be unlikely. Because the rock had a mild temperature history, these molecuies could have survived since Archean time. Because of all the evidence, the furans and alkanes are quite likely biochemical fossils.

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Further Rb-Sr age and isotope data on Early and Late Archaean rocks from the Rhodesian craton

Cited by 41 publications

References 8 publications

Juvenile crust formation in the Zimbabwe Craton deduced from the O-Hf isotopic record of 3.8–3.1 Ga detrital zircons

Juvenile crust formation in the Zimbabwe Craton deduced from the O-Hf isotopic record of 3.8–3.1 Ga detrital zircons

Ca isotope fingerprints of early crust-mantle evolution

2,5-Dimethylfuran from ≈2.7 × 10 ⁹ -year-old Rupemba—Belingwe stromatolite, Rhodesia: Potential evidence for remnants of carbohydrates

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Further Rb-Sr age and isotope data on Early and Late Archaean rocks from the Rhodesian craton

Cited by 41 publications

References 8 publications

Juvenile crust formation in the Zimbabwe Craton deduced from the O-Hf isotopic record of 3.8–3.1 Ga detrital zircons

Juvenile crust formation in the Zimbabwe Craton deduced from the O-Hf isotopic record of 3.8–3.1 Ga detrital zircons

Ca isotope fingerprints of early crust-mantle evolution

2,5-Dimethylfuran from ≈2.7 × 10 9 -year-old Rupemba—Belingwe stromatolite, Rhodesia: Potential evidence for remnants of carbohydrates

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2,5-Dimethylfuran from ≈2.7 × 10 ⁹ -year-old Rupemba—Belingwe stromatolite, Rhodesia: Potential evidence for remnants of carbohydrates