Earth’s first stable continents did not form by subduction

Johnson, Tim; Brown, Michael; Gardiner, Nicholas J.; Kirkland, Christopher L.; Smithies, R. Hugh

doi:10.1038/nature21383

Cited by 337 publications

(202 citation statements)

References 35 publications

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“…Figure presents primitive mantle (Sun & McDonough, ) normalized trace elements and a Quartz‐Alkali Feldspar‐Plagioclase classification plot; notably, all samples exhibit broadly similar large‐ion lithophile element and light rare earth element enrichment, and distinctive negative Nb anomalies. These characteristics are typical of magmas formed in a suprasubduction type setting; however, it is well documented that such characteristics are not exclusive and may represent hydrous melting of mafic rocks in other settings (e.g., Johnson et al, ; Moyen, ; Moyen & Laurent, ; Nagel et al, ). The notable feature is that there is no apparent change in geochemical signature that may also reflect a change in geodynamic regime, that is, from plume‐derived to subduction‐derived magmas.…”

Section: Resultsmentioning

confidence: 99%

Capturing the Mesoarchean Emergence of Continental Crust in the Coorg Block, Southern India

Santosh

2018

Geophysical Research Letters

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The emergence of Earth's continental crust above sea level is debated. To assess whether emergence can be observed at a regional scale, we present zircon U‐Pb‐Hf‐O isotope data from magmatic rocks of the Coorg Block, southern India. A 3.5‐Ga granodiorite records the earliest felsic crust in the region. Younger phases of magmatism at 3.37–3.27 and 3.19–3.14 Ga, comprising both reworked crust and juvenile material, record successive crustal maturation. We interpret an elevation in δ18O through time as an increase in both the amount of sediment recycling and hence, crustal thickening, as well as an increase in the emerged area of continental crust available for weathering. Geochemical signatures do not point to any apparent change in geodynamic regime. We interpret the isotopic evolution of these rocks as solely reflecting regional emergence and thickening of the continental crust, assisted by the increasing strength of the lithosphere.

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Section: Resultsmentioning

confidence: 99%

Capturing the Mesoarchean Emergence of Continental Crust in the Coorg Block, Southern India

Santosh

2018

Geophysical Research Letters

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“…The tectonic environments and geodynamic processes responsible for the stabilization of Earth's first continental nuclei have long been—and remain—a topic of heated debate (e.g. Bédard, ; Brown & Johnson, ; Foley, Buhre, & Jacob, ; Hamilton, ; Hawkesworth et al., ; Johnson et al., ; Palin, White, & Green, ; Roberts, Van Kranendonk, Parman, & Clift, ).…”

Section: Discussionmentioning

confidence: 99%

“…These relations now allow for in‐depth, quantitative investigation of granulite facies metamorphism in the early Earth, and the formation and long‐term evolution of Archean continental crust (e.g. Johnson, Brown, Gardiner, Kirkland, & Smithies, ; Palin, White, & Green, ; White et al., ).…”

Section: Introductionmentioning

confidence: 99%

New constraints on granulite facies metamorphism and melt production in the Lewisian Complex, northwest Scotland

Feisel

White

Palin

et al. 2018

Journal Metamorphic Geology

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In this study, we investigate the metamorphic history of the Assynt and Gruinard blocks of the Archean Lewisian Complex, northwest Scotland, which are considered by some to represent discrete crustal terranes. For samples of mafic and intermediate rocks, phase diagrams were constructed in the Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–O2 (NCKFMASHTO) system using whole‐rock compositions. Our results indicate that all samples equilibrated at similar peak metamorphic conditions of ~8–10 kbar and ~900–1,000°C, consistent with field evidence for in situ partial melting and the classic interpretation of the central region of the Lewisian Complex as representing a single crustal block. Melt‐reintegration modelling was employed in order to estimate probable protolith compositions. Phase equilibria calculated for these modelled undepleted precursors match well with those determined for a subsolidus amphibolite from Gairloch in the southern region of the Lewisian Complex. Both subsolidus lithologies exhibit similar phase relations and potential melt fertility, with both expected to produce orthopyroxene‐bearing hornblende granulites, with or without garnet, at the conditions inferred for the Badcallian metamorphic peak. For fully hydrated protoliths, prograde melting is predicted to first occur at ~620°C and ~9.5 kbar, with up to 45% partial melt predicted to form at peak conditions in a closed‐system environment. Partial melts calculated for both compositions between 610 and 1,050°C are mostly trondhjemitic. Although the melt‐reintegrated granulite is predicted to produce more potassic (granitic) melts at ~700–900°C, the modelled melts are consistent with the measured compositions of felsic sheets from the central region Lewisian Complex.

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“…The majority of Archean TTGs feature a distinctive trace element signature (e.g., high La/Yb and low Nb/Ta ratios) that requires their separation from a garnet‐, hornblende‐, plagioclase‐, and rutile‐bearing source rock (Moyen & Martin, ), such as garnet amphibolite or garnet granulite. These lithologies stabilize in metamorphosed mafic rock types along geothermal gradients of 900–1000 °C/GPa (Johnson et al, ; Palin et al, ). Partial melting of mafic crust must therefore have occurred at high‐pressure conditions and would produce high amounts of dense residuum, which is not preserved in the Archean record.…”

Section: Introductionmentioning

confidence: 99%

Generation of Earth's Early Continents From a Relatively Cool Archean Mantle

Piccolo

Palin

Kaus

et al. 2019

Geochem Geophys Geosyst

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Several lines of evidence suggest that the Archean (4.0–2.5 Ga) mantle was hotter than today's potential temperature (TP) of 1350 °C. However, the magnitude of such difference is poorly constrained, with TP estimation spanning from 1500 to 1600 °C during the Meso‐Archean (3.2–2.8 Ga). Such differences have major implications for the interpreted mechanisms of continental crust generation on the early Earth, as their efficacy is highly sensitive to the TP. Here we integrate petrological modeling with thermomechanical simulations to understand the dynamics of crust formation during Archean. Our results predict that partial melting of primitive oceanic crust produces felsic melts with geochemical signatures matching those observed in Archean cratons from a mantle TP as low as 1450 °C thanks to lithospheric‐scale RayleighTaylor‐type instabilities. These simulations also infer the occurrence of intraplate deformation events that allow an efficient transport of crustal material into the mantle, hydrating it.

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Earth’s first stable continents did not form by subduction

Cited by 337 publications

References 35 publications

Capturing the Mesoarchean Emergence of Continental Crust in the Coorg Block, Southern India

Capturing the Mesoarchean Emergence of Continental Crust in the Coorg Block, Southern India

New constraints on granulite facies metamorphism and melt production in the Lewisian Complex, northwest Scotland

Generation of Earth's Early Continents From a Relatively Cool Archean Mantle

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