∼ 3710 and ⪖ 3790 Ma volcanic sequences in the Isua (Greenland) supracrustal belt; structural and Nd isotope implications

Nutman, Allen P.; Bennett, Vickie C.; Friend, C. R. L.; Rosing, Minik T.

doi:10.1016/s0009-2541(97)00084-3

Cited by 184 publications

(130 citation statements)

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“…Ma detrital zircons (Nutman et al, 1997;2010), attesting to their sedimentary origins and a maximum depositional age of 3810 Ma. The calc-silicate rocks associated with the dolomites are interpreted as interlayered cherts and dolomites, which during metamorphism reacted and gave rise to diopside + quartz or diopside + dolomite rocks.…”

Section: Field Relationshipsmentioning

confidence: 92%

“…The belt is bounded by metaplutonic complexes, with that on the north being dominated by 3700-3690 Ma tonalite protoliths and 3650-3640 Ma granite sheets, and that to the south being dominated by 3820-3795 Ma tonalite protoliths (Nutman et al, , 1996(Nutman et al, , 1997(Nutman et al, , 2000Crowley et al, 2002;Crowley, 2003;). The southern part of the belt is intruded by ~3800 Ma tonalite sheets which were emplaced into already deformed volcanic and sedimentary rocks (Nutman et al, 1996, 1997, Crowley, 2003. To the west, the belt is in tectonic contact with Mesoarchaean gneisses and supracrustal rocks , whereas eastwards it is coverage by the Inland Ice.…”

Section: Geology Of the Isua Supracrustal Beltmentioning

confidence: 99%

“…The southern part is dominated by ~3800 Ma rocks, whereas the northern and central portions consist of ~3700 Ma rocks ( Fig. 1; Nutman et al, 1996Nutman et al, , 1997Nutman and Friend, 2009, and references therein). Between the 3800 and 3700 Ma portions of the belt there is the dividing sedimentary unit, which contains 3940-3760 Ma detrital zircons Nutman et al, 2009).…”

Section: Geology Of the Isua Supracrustal Beltmentioning

confidence: 99%

“…This dividing sedimentary unit was interpreted to have an unconformity at its southern edge and its northern edge is an Eoarchaean mylonite, separating it from the ~ 3700 Ma terrane to the north Nutman et al, 2009). Therefore, it has been proposed that the ~3800 and 3700 Ma terranes evolved separately from each other and were tectonically juxtaposed before 3660 Ma, the age of the first igneous intrusions common to both terranes (Nutman et al, 1997(Nutman et al, , 2002Crowley, 2003).…”

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%

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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: Field Relationshipsmentioning

confidence: 92%

Section: Geology Of the Isua Supracrustal Beltmentioning

confidence: 99%

Section: Geology Of the Isua Supracrustal Beltmentioning

confidence: 99%

Section: Geology Of the Isua Supracrustal Beltmentioning

confidence: 99%

Section: Geology Of the Isua Supracrustal Beltmentioning

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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A 3.51 Ga bimodal volcanics‐BIF‐ultramafic succession from Singhbhum Craton: implications for Palaeoarchaean geodynamic processes from the oldest greenstone succession of the Indian subcontinent

et al. 2011

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The Palaeoarchaean greenstone belt of the southern Iron Ore Group (SIOG) (3.51 Ga) in the Singhbhum Craton, eastern India, includes lowstrained and low-greenstone grade bimodal volcanics, Banded Iron Formation (BIF) and chromiferous ultramafics as enclaves within tonalitetrondjhemite-granodiorite (TTG) granitoids, collectively referred to as the Singhbhum Granite (3.4 Ga to 3.1 Ga). The succession comprises, from base to top, a lower unit of massive and pillowed basalt conformably overlain by dacitic lava and pyroclastics which in turn is overlain by a major BIF unit. The ultramafics are juxtaposed with the volcanics-BIF succession along a thrust fault. The lithological association of pillow lava, subaqueous dacitic lava and pyroclastic rocks and BIF collectively, suggests that the entire succession was deposited in a deep-marine depositional setting. The ash-poor dacitic volcanic rock succession with evidences of a transition from suppressed-volatile deep-water lava flow and pyroclastics to more evolved mass-flow deposits with increasing trend of subaqueous flow transformation, records a transition from a deep-water low-height volcanic chain to a shallower subaqueous eruption in an aggradational volcanic chain. Geochemical proxies from the bimodal volcanics and ultramafics showing enrichment of La/Nb, Th/Nb, Th/La, Ba/La, Pb/Ce, depletion in Nb-Ta relative to neighbouring REE, together with tectonic discrimination criteria using Nb, Y, Zr, Ti compositions, suggest an extending oceanic arc-forearc geodynamic setting similar to many of the Phanerozoic supra-subduction zone ophiolites where ophiolite development in the extending upper plate in a relatively short time span is facilitated by slab rollback processes. The positive Eu-anomaly together with high Y/Ho values from the BIFs also suggests their deposition in close proximity to spreading centres that might have developed over a rifted arc. The bimodal volcanic rock-BIF-ultramafic succession of the SIOG with evidence of a convergent margin geodynamic setting is an important example for Palaeoarchaean plate tectonic processes operating on Earth.

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From Fossils to Astrobiology

Seckbach¹,

Walsh²

2008

Cellular Origin, Life in Extreme Habitats and Astrobiology

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∼ 3710 and ⪖ 3790 Ma volcanic sequences in the Isua (Greenland) supracrustal belt; structural and Nd isotope implications

Cited by 184 publications

References 45 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

A 3.51 Ga bimodal volcanics‐BIF‐ultramafic succession from Singhbhum Craton: implications for Palaeoarchaean geodynamic processes from the oldest greenstone succession of the Indian subcontinent

From Fossils to Astrobiology

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