Stratigraphic and geochemical evidence for the depositional environment of the early archaean isua supracrustal belt, southern west greenland

Nutman, Allen P.; Allaart, J.H; Bridgwater, D.; Dimroth, Erich; Rosing, Minik T.

doi:10.1016/0301-9268(84)90010-x

Cited by 166 publications

(112 citation statements)

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“…Nutman et al (1984) re-evaluated the unit, and concurred with an acid volcanic and/or volcano-sedimentary origin. Lines of evidence supporting this were the rare preservation of graded layering, and survival of microtextures resembling fiamme within the putative volcanic bombs ( Fig.…”

Section: Previous Studiesmentioning

confidence: 75%

“…The dominant lithologies within both segments of the belt are similar, comprising amphibolites derived from basaltic, picritic and boninitic protoliths (the latter in the ~ 3700 Ma sequence only), felsic volcanic and sedimentary rocks and chemical sedimentary rocks, particularly chert and banded iron formation (BIF; e.g., Allaart, 1976;Nutman et al, 1984Nutman et al, , 2007Nutman et al, , 2009Nutman et al, , 2010Nutman et al, , 2013Komiya et al, 1999;Polat et al, 2002;Polat and Hofmann 2003, Bolhar et al, 2004, 2005Furnes et al, 2007;Jenner et al, 2009). Plutonic mafic rocks are much less common within the belt, but include some gabbros and ultramafic rocks that were derived from cumulates in layered gabbro intrusions (e.g., Dymek et al, 1988) and from the upper mantle (Friend and Nutman, 2011).…”

Section: Geology Of the Isua Supracrustal Beltmentioning

confidence: 99%

“…Thus primary volcanic and sedimentary structures have survived in only a few places. The commonest relict structures are pillows within mafic rocks, graded layering in felsic volcano-sedimentary rocks and layering in banded iron formation (e.g., Nutman et al, 1984;1997Komiya et al, 1999;Solvang, 1999;Furnes et al, 2007). In this paper we discuss the origin and chemical modification of a felsic schist unit within the ~3800 Ma southern portion of the belt.…”

Section: Geology Of the Isua Supracrustal Beltmentioning

confidence: 99%

“…However, graded layering is preserved within it locally ( Fig. 4a in Nutman et al, 1984). Much debated are features found in the core of a steeply plunging parasitic fold in the central segment of the unit on the eastern shores of the lake with an altitude 678 m, where the unit features prolate nodular structures up to 1 m long set in a more strongly eroded matrix (Fig.…”

Section: Previous Studiesmentioning

confidence: 99%

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3806Ma Isua rhyolites and dacites affected by low temperature Eoarchaean surficial alteration: Earth's earliest weathering

Nutman

Bennett

Chivas

et al. 2015

Precambrian Research

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This paper reports evidence for Earth's oldest-recognised low temperature alteration, at ∼3800 Ma. Potassic felsic schists with a protolith age of 3806 ± 2 Ma form a ∼30 km long unit in the amphibolite facies, deformed, Isua supracrustal belt (West Greenland). At a single locality, boudinaged layers (nodules) within the schists are low strain zones: they are fine-grained, weakly feldspar-phyric, contain quartz amygdules and have fiammelike structures, all supporting a volcanic protolith. The nodules and surrounding schistose matrix contain abundant, 100-50 μm, euhedral, oscillatory zoned 3806 Ma zircons. The rare earth patterns of the zircons indicate crystallisation was magmatic. Some zircons contain axial lobate voids indicating that they grew at low pressure as the magma exsolved a fluid. Ti-in-zircon thermometry indicates crystallisation temperatures of 750-650 °C. Taken together, these zircon features indicates growth at eutectic temperatures in a hypabyssal chamber as the magma was exsolving a fluid phase. The magmatic zircons have ɛHf initial values of ∼0 and δ18OVSMOW of +5.0‰ ( Hiess et al., 2009), showing that the source of the volcanic rocks was devoid of assimilated markedly older or weathered crustal material, and probably essentially juvenile. In contrast, the whole rock δ18OVSMOW values are elevated at +14.7 to +16.2‰, indicative of superimposed lowtemperature alteration processes. The nodules and matrix schists have non-igneous bulk compositions, exemplified by strong enrichment in K2O and depletion in Na2O. They are depleted in Sr, have no negative Eu anomalies, but have high Rb/Sr, with an Rb-Sr age of 3760 ± 140 Ma ( Jacobsen and Dymek, 1988). This indicates that the alteration involving strong degradation of plagioclase occurred in the Eoarchaean. Trace element compositions and establishment of alteration vectors suggest the protoliths were likely rhyolitic and dacitic in composition. The strongest-modified matrix schist compositions contain biotite ± calcite ± dolomite with increase in MgO relative to the nodules, which indicates early magnesian carbonate growth. The whole-rock chemistry, decoupling of the igneous zircon and whole-rock oxygen isotope signatures and the Rb-Sr dating indicate that after eruption, the 3806 Ma felsic volcanic rocks underwent Eoarchaean lowtemperature potassic alteration with weathering and groundwater circulation the most likely process. The geochemistry of the Isua felsic schists is compared with that of better-preserved volcanic rocks where the alteration conditions are known. This suggests a subaerial environment. The carbonatisation of the Isua felsic schists demonstrates drawdown of atmospheric CO2 into rocks made porous by the weathering.

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Section: Previous Studiesmentioning

confidence: 75%

Section: Geology Of the Isua Supracrustal Beltmentioning

confidence: 99%

Section: Geology Of the Isua Supracrustal Beltmentioning

confidence: 99%

Section: Previous Studiesmentioning

confidence: 99%

See 2 more Smart Citations

3806Ma Isua rhyolites and dacites affected by low temperature Eoarchaean surficial alteration: Earth's earliest weathering

Nutman

Bennett

Chivas

et al. 2015

Precambrian Research

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“…Even dissolved bicarbonate ions in sea water may have been irradiated to produce organic carbon compounds such as organic acids, formaldehyde and methanol, as this can be demonstrated experimentally, both by self-irradiation from carbon-14 in the bicarbonate and by irradiation from external sources (Albarrán et al, 1987;Albarrán and Collins, 1998). The record of limestones back to the early Archean (Nutman et al, 1984) shows that sea water was bicarbonate-saturated. Radioactive grain concentrations in beaches at the sea margins were the most likely sites for this process.…”

Section: Sources Of Carbon and Environments On The Early Earthmentioning

confidence: 97%

Mineral Radioactivity in Sands as a Mechanism for Fixation of Organic Carbon on the Early Earth

Parnell

2004

Orig Life Evol Biosph

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Abstract. Irradiation of organic molecules by mineral radioactivity is a feasible alternative to cosmic irradiation to precipitate solid organic carbon-rich matter on the early Earth. Radioactive (uranium-and thorium-rich) minerals have been concentrated at the Earth's surface, and accumulated accretionary coatings of carbon due to irradiation, since early Archean times. The organic accretion process could have occurred at the surface or in the sub-surface, and is independent of a terrestrial or extraterrestrial source for the carbon.

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Accretion to Earth and Moon ∼3.85 Ga

Mojzsis

Ryder

2001

Accretion of Extraterrestrial Matter Throughout Earth’s History

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The lunar record provides a means of estimating post-accretionary impact influences on the early Earth and a comparison with what we can more directly infer from the Earth's own rocks. In the period from about 3.9 to about 3.8 Ga there was considerable impacting on the Moon with evidence for concurrent marine sedimentation on Earth. This was a time interval in which the impactor flux to the lunar surface was orders of magnitude greater than the present rate; massive impacts as well as an enhanced background flux of extraterrestrial matter should have likewise affected the surface of early Earth. As yet, no unequivocal evidence for a "Late Heavy Bombardment of the Earth" has been established from direct measurement of terrestrial crustal rocks. The lack of a signal of the bombardment on Earth may be due to the fact that: (i) the oldest sediments do not overlap with the bombardment era, (ii) the bombardment was less intense than previously thought, (iii) sedimentation was extremely rapid so as to dilute any extraterrestrial signal, (iv) sample volumes yet analyzed undersample extra-terrestrial input, or (v) windows for sampling elevated fluxes of extraterrestrial bodies were very short between long periods of relative calm. Further extensive studies of the oldest known sediments will be needed to resolve the issues raised in this paper.

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Stratigraphic and geochemical evidence for the depositional environment of the early archaean isua supracrustal belt, southern west greenland

Cited by 166 publications

References 40 publications

3806Ma Isua rhyolites and dacites affected by low temperature Eoarchaean surficial alteration: Earth's earliest weathering

3806Ma Isua rhyolites and dacites affected by low temperature Eoarchaean surficial alteration: Earth's earliest weathering

Mineral Radioactivity in Sands as a Mechanism for Fixation of Organic Carbon on the Early Earth

Accretion to Earth and Moon ∼3.85 Ga

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