146Sm–142Nd evidence from Isua metamorphosed sediments for early differentiation of the Earth's mantle

Caro, Guillaume; Bourdon, Bernard; Birck, J. L.; Moorbath, S.

doi:10.1038/nature01668

Cited by 273 publications

(171 citation statements)

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“…These data provide strong evidence for a mantle value of ε Nd =+3 at 3850 Ma and strengthen arguments for rapid early depletion of at least portions of the upper mantle (e.g. Bennett et al, 1993;Caro et al, 2003). The major and trace element compositions of these tonalites are similar to other Archaean TTG suites both in West Greenland (Nutman et al, 1999) Complex TTG (Nutman et al, 1999) and the open square is average value for >3500 Ma TTG from Martin et al (2005).…”

Section: Discussionmentioning

confidence: 51%

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∼3,850 Ma tonalites in the Nuuk region, Greenland: geochemistry and their reworking within an Eoarchaean gneiss complex

Nutman

Bennett

Friend

et al. 2007

Contrib Mineral Petrol

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Hidaka, H. (2007). ~3,850 Ma tonalites in the Nuuk region, Greenland: geochemistry and their reworking within an Eoarchaean gneiss complex. Contributions to Mineralogy and Petrology, 154 (4), 385-408. ~3,850 Ma tonalites in the Nuuk region, Greenland: geochemistry and their reworking within an Eoarchaean gneiss complex AbstractThe Eoarchaean (>3,600 Ma) Itsaq Gneiss Complex of southern West Greenland is dominated by polyphase orthogneisses with a complex Archaean tectonothermal history. Some of the orthogneisses have c. 3,850 Ma zircons, and they vary from rare single phase metatonalites to more common complexly banded migmatites. This is due to heterogeneous strain, in situ anatexis and granitic veining superimposed during younger tectonothermal events. In the single-phase tonalites with c. 3,850 Ma zircon, oscillatory-zoned prismatic zircon is all 3,850 Ma old, but shows patchy ancient loss of radiogenic Pb. SHRIMP spot analyses and laser ablation ICP-MS depth profiling show that thin (usually < 10 μm) younger (3,590 Ma and Neoarchaean) shells of lower Th/U metamorphic zircon are present on these 3,850 Ma zircons. Several samples with this simple zircon population occur on islands near Akilia. In contrast, migmatites usually contain more complex zircon populations, with often more than one generation of igneous zircon present. Additional zircon dating of banded gneisses across the Complex shows that samples with c. 3,850 Ma igneous zircon are not just a phenomenon restricted to Akilia and adjacent islands. For example, migmatites from Itilleq (c. 65 km from Akilia) contain variable amounts of oscillatory-zoned 3,850 Ma and 3,650 Ma zircon, interpreted, respectively, as the rock age and the time of crustal melting under Eoarchaean metamorphism. With only 110-140 ppm Zr in the tonalites and likely magmatic temperatures of >850°C, zircon solubilitymelt composition relationships show that they were only one-third saturated in zircon. Any zircon entrained in the precursor magmas would thus have been highly soluble. Combined with the cathodoluminesence imaging, this demonstrates that the c. 3,850 Ma oscillatory zoned zircon crystallised out of the melt and hence gives a magmatic age. Thus the rare well-preserved tonalites and palaeosome in migmatites testify that c. 3,850 Ma quartzo -feldspathic rocks are a widespread (but probably minor) component in the Itsaq Gneiss Complex. C. 3,850 Ma zircon with negative Eu anomalies (showing growth in felsic systems) also occurs as detrital grains in rare c. 3,800 Ma metaquartzites and as inherited grains in some 3,660 Ma granites (sensu stricto). These demonstrate that still more c. 3,850 Ma rocks were present, but were recycled into Eoarchaean sediments and crustally derived granites. The major and trace element characteristics (e.g. LREE enrichment, HREE depletion, low MgO) of the best-preserved c. 3,850 Ma rocks are typical of Archaean TTG suites, and thus argue for crust formation processes involving important contributions from melting of hydrated mafic crust to the...

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Section: Discussionmentioning

confidence: 51%

“…Bennett et al, 1993;Caro et al, 2003), that generating ε Nd =+3 before 3850 Ma in the upper mantle source of the ancient tonalites requires rapid early depletion (increase in Sm/Nd).…”

Section: Depletion History Of the Pre-3850 Ma Mantle From 147 Sm-143 mentioning

confidence: 99%

∼3,850 Ma tonalites in the Nuuk region, Greenland: geochemistry and their reworking within an Eoarchaean gneiss complex

Nutman

Bennett

Friend

et al. 2007

Contrib Mineral Petrol

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“…There is now clear evidence for an early terrestrial mantle differentiation event (Caro et al 2003) and the remaining questions are related to the exact timing of this differentiation as well as the composition of the BE. The recent analyses of 142 Nd in meteorites (Boyet & Carlson 2005) have revealed that (i) the composition of the Earth's mantle is distinct from that of meteorites and (ii) the two main classes of chondrites (ordinary and carbonaceous chondrites) also have a distinct 142 Nd-isotope composition despite having quite similar Sm/Nd ratios.…”

Section: Constraints On the Early Differentiation Of The Earthmentioning

confidence: 99%

Early differentiation of the Earth and the Moon

Bourdon

Touboul

Caro

et al. 2008

Phil. Trans. R. Soc. A.

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We examine the implications of new 182 W and 142 Nd data for Mars and the Moon for the early evolution of the Earth. The similarity of 182 W in the terrestrial and lunar mantles and their apparently differing Hf/W ratios indicate that the Moon-forming giant impact most probably took place more than 60 Ma after the formation of calcium-aluminium-rich inclusions (4.568 Gyr). This is not inconsistent with the apparent U-Pb age of the Earth. The new 142 Nd data for Martian meteorites show that Mars probably has a superchondritic Sm/Nd that could coincide with that of the Earth and the Moon. If this is interpreted by an early mantle differentiation event, this requires a buried enriched reservoir for the three objects. This is highly unlikely. For the Earth, we show, based on new mass-balance calculations for Nd isotopes, that the presence of a hidden reservoir is difficult to reconcile with the combined 142 Nd-143 Nd systematics of the Earth's mantle. We argue that a likely possibility is that the missing component was lost during or prior to accretion. Furthermore, the 142 Nd data for the Moon that were used to argue for the solidification of the magma ocean at ca 200 Myr are reinterpreted. Cumulate overturn, magma mixing and melting following lunar magma ocean crystallization at 50-100 Myr could have yielded the 200 Myr model age.

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“…However, the long-lived 147 Sm-143 Nd system alone cannot give an exact time of depletion. The extinct 146 Nd system provided the first clear evidence of very early mantle depletion (Harper & Jacobsen 1992;Jacobsen & Harper 1996) and has now been extended to many new samples of the Isua supracrustal belt (Boyet et al 2003;Caro et al 2003Caro et al , 2006Bennett et al 2007 Bizzarro et al 2003;Jacobsen 2003b). Thus, the coupled 147,146 142 Nd chronometer remains the most powerful tool to study how the silicate Earth evolved.…”

Section: (D ) Proposed Scenariosmentioning

confidence: 99%

Isotopes as clues to the origin and earliest differentiation history of the Earth

Jacobsen

Ranen

Petaev

et al. 2008

Phil. Trans. R. Soc. A.

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Measurable variations in 182 W/ 183 W, 142 Nd/ 144 Nd, 129 Xe/ 130 Xe and 136 Xe Pu / 130 Xe in the Earth and meteorites provide a record of accretion and formation of the core, early crust and atmosphere. These variations are due to the decay of the now extinct nuclides 182 Hf, 146 Sm, 129 I and 244 Pu. The l82 Hf– 182 W system is the best accretion and core-formation chronometer, which yields a mean time of Earth's formation of 10 Myr, and a total time scale of 30 Myr. New laser shock data at conditions comparable with those in the Earth's deep mantle subsequent to the giant Moon-forming impact suggest that metal–silicate equilibration was rapid enough for the Hf–W chronometer to reliably record this time scale. The coupled 146 Sm– 147 Sm chronometer is the best system for determining the initial silicate differentiation (magma ocean crystallization and proto-crust formation), which took place at ca 4.47 Ga or perhaps even earlier. The presence of a large 129 Xe excess in the deep Earth is consistent with a very early atmosphere formation (as early as 30 Myr); however, the interpretation is complicated by the fact that most of the atmospheric Xe may be from a volatile-rich late veneer.

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146Sm–142Nd evidence from Isua metamorphosed sediments for early differentiation of the Earth's mantle

Cited by 273 publications

References 29 publications

∼3,850 Ma tonalites in the Nuuk region, Greenland: geochemistry and their reworking within an Eoarchaean gneiss complex

∼3,850 Ma tonalites in the Nuuk region, Greenland: geochemistry and their reworking within an Eoarchaean gneiss complex

Early differentiation of the Earth and the Moon

Isotopes as clues to the origin and earliest differentiation history of the Earth

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