The zircon geochronology of the Akilia association and Isua supracrustal belt, West Greenland

Baadsgaard, H.; Nutman, Allen P.; Bridgwater, D.; Rosing, Minik T.; McGregor, V. R.; Allaart, J.H

doi:10.1016/0012-821x(84)90154-7

Cited by 101 publications

(22 citation statements)

References 25 publications

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“…During the early exploration of the belt (Allaart, 1976), these structures were interpreted as acid volcanic bombs. Based on this volcanic interpretation, the nodular structures were the target of the first U-Pb zircon geochronology on Isua supracrustal belt rocks, with bulk analysis and small fraction techniques giving upper concordia intercept ages of 3824 +12 -9 and 3813 +21 -14 Ma (Michard-Vitrac et al, 1977;Baadsgaard et al, 1984). Compston et al (1986) presented a SHRIMP weighted mean 207 Pb/ 206 Pb age of 3806±2 Ma (2σ).…”

Section: Previous Studiesmentioning

confidence: 99%

“…Heiss et al (2009) reported hafnium and oxygen isotopic data from aliquots of the same zircon separates from samples 248202 (matrix) and 248203 (nodule) that were used by Baadsgaard et al (1984) and Compston et al (1986) (Baadsgaard et al, 1986a).…”

Section: Previous Studiesmentioning

confidence: 99%

“…Zircons in 248203 (nodule) and 248202 (matrix) samples were U-Pb dated first by Baadsgaard et al (1984) by bulk analysis and then by Compston et al (1986) Given the large amount of published isotopic data on these zircons, they were targeted for detailed petrographic study.…”

Section: Morphologymentioning

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: 99%

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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“…Contrarily to TTG that emplaced deep into the crust, supracrustal deposited or erupted at the surface of the Earth (Figure 4.13). At Isua, zircons gave an age of 3.812 ± 0.014 Ga (Baadsgaard et al, 1984). In Akilia Island, the Amitsoˆq tonalite dated at 3.872 ± 0.010 Ga by Nutman et al is intrusive (dyke) into a banded iron formation (BIF) thus demonstrating that this sedimentary rock is older than 3.872 Ga. Figure 4.13.…”

Section: Isua and Akilia Greenstone Belt (Greenland)mentioning

confidence: 99%

4. Building of a Habitable Planet

et al. 2006

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Abstract. Except the old Jack Hills zircon crystals, it does not exit direct record of the first 500 Ma of the Earth history. Consequently, the succession of events that took place during this period is only indirectly known through geochemistry, comparison with other telluric planets, and numerical modelling. Just after planetary accretion several episodes were necessary in order to make life apparition and development possible and to make the Earth surface habitable. Among these stages are: the core differentiation, the formation of a magma ocean, the apparition of the first atmosphere, oceans and continents as well as the development of magnetic field and of plate tectonics. In the same time, Earth has been subject to extraterrestrial events such as the Late Heavy Bombardment (LHB) between 3.95 and 3.8 Ga. Since 4.4-4.3 Ga, the conditions for pre-biotic chemistry and appearance of life were already met (liquid water, continental crust, no strong meteoritic bombardment, etc...). This does not mean that life existed as early, but this demonstrates that all necessary conditions assumed for life development were already present on Earth.

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“…15. The age of the Isua Supracrustal Belt ranges from 3.71 to 3.81 Gyr (14)(15)(16)(17)(18)(19); (ii) two basalts from Loihi Seamount, Hawaii, which is located 30 km south of Kilauea volcano; (iii) one Icelandic picrite from the neovolcanic zone of Theistareykir (Storaviti N65°88′, W16°85′) located in the northeastern part of Iceland; (iv) three kimberlites from Safartoq, S.W. Greenland (see ref.…”

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confidence: 99%

Coupled ¹⁸² W- ¹⁴² Nd constraint for early Earth differentiation

Moynier

Yin

Irisawa

et al. 2010

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

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Recent high precision 142 Nd isotope measurements showed that global silicate differentiation may have occurred as early as 30-75 Myr after the Solar System formation [Bennett V, et al. (2007) Science 318:1907-1910. This time scale is almost contemporaneous with Earth's core formation at ∼30 Myr [Yin Q, et al. (2002) 142 Nd anomalies, all have a homogeneous W isotopic composition, which is ∼2ε-unit more radiogenic than the chondritic value. By using a 3-stage model calculation that describes the isotopic evolution in chondritic reservoir and core segregation, as well as silicate differentiation, we show that the W isotopic composition of terrestrial samples provides the most stringent time constraint for early core formation (27.5-38 Myr) followed by early terrestrial silicate differentiation that is consistent with the terrestrial 142 Nd anomalies.hafnium | tungsten | hidden reservoir | Hawaii | Iceland S hort-lived chronometers provide evidence for the rapid differentiation of planet Earth. In particular, 182 Hf-182 W (T 1∕2 ¼ 8.9 Myr) and 146 Sm-142 Nd (T 1∕2 ¼ 103 Myr) have been used to constrain the age of core formation (1, 2) and of silicate differentiation (3-7), respectively. All terrestrial rocks analyzed so far are characterized by 182 W∕ 184 W ratios that are ∼2ε-unit (see Table 1 caption for definition) higher than those of chondrites, which is commonly interpreted as evidence for early metal-silicate segregation and core formation (1, 2). Terrestrial rocks are also characterized by ∼0.2ε excess of 142 Nd∕ 144 Nd relative to chondrites (3). This excess has been interpreted as evidence for early global differentiation of the silicate Earth during the first 30-75 Myr of the Solar System, where the resulting enriched silicate reservoir is permanently stored at the base of the lowermost mantle (3), Hadean crust (8), or in the roots of cratons (9) (see SI Text for comments on alternative theories).Whereas tungsten is a moderately siderophile element, it is also highly incompatible during silicate partial melting; in fact, W, U, and Th all have similar partition coefficients (10, 11). In contrast, Hf, which is a lithophile element, is only moderately incompatible during silicate partial melting (11). Consequently, W is strongly fractionated from Hf during silicate melting events (12), resulting in oceanic and continental crust that is enriched in W (∼400 and ∼1;000 ppb, respectively) relative to the mantle (∼16 ppb) (12, 13). Therefore, mantle differentiation/melting events that occurred early enough in Earth's history (35-70 Myr), as constrained by 142 Nd data, should fractionate Hf/W ratios and result in ε 182 W anomalies with time. The ∼2ε 182 W anomalies observed between terrestrial rocks and chondrites (refs. 1 and 2 and this work) should, therefore, be attributed to the collective effects of both silicate melting (crust/mantle differentiation), as well as silicate/metal fractionation (core/mantle differentiation), and not solely because of the silicate/metal fractionation as previously thought ...

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The zircon geochronology of the Akilia association and Isua supracrustal belt, West Greenland

Cited by 101 publications

References 25 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

4. Building of a Habitable Planet

Coupled ¹⁸² W- ¹⁴² Nd constraint for early Earth differentiation

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The zircon geochronology of the Akilia association and Isua supracrustal belt, West Greenland

Cited by 101 publications

References 25 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

4. Building of a Habitable Planet

Coupled 182 W- 142 Nd constraint for early Earth differentiation

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Coupled ¹⁸² W- ¹⁴² Nd constraint for early Earth differentiation