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Earth's first stable continents did not form by subduction
Tim E. Johnson,Michael Brown,Nicholas J. Gardiner,Christopher L. Kirkland,R. Hugh Smithies +4 more
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Johnson et al. as discussed by the authors performed phase equilibria modelling of the Coucal basalts from Western Australia and confirmed their suitability as parent rocks of the early continental crust of the Earth's first continents.Abstract:
Phase equilibria modelling of rocks from Western Australia confirms that the ancient continental crust could have formed by multistage melting of basaltic ‘parents’ along high geothermal gradients—a process incompatible with modern-style subduction Tim Johnson et al perform phase equilibria modelling of the Coucal basalts from Western Australia and confirm their suitability as parent rocks of the Archaean continental crust The authors suggest that these early crustal rocks were produced by 20–30 per cent melting along high geothermal gradients They conclude that the production and stabilization of the first continents required a protracted, multistage process When coupled with the high geothermal gradients, this suggests that the continents did not form by subduction Instead it favours a 'stagnant lid' regime in the early Archaean eon in which a single, rigid plate lay over the mantle The geodynamic environment in which Earth’s first continents formed and were stabilized remains controversial1 Most exposed continental crust that can be dated back to the Archaean eon (4 billion to 25 billion years ago) comprises tonalite–trondhjemite–granodiorite rocks (TTGs) that were formed through partial melting of hydrated low-magnesium basaltic rocks2; notably, these TTGs have ‘arc-like’ signatures of trace elements and thus resemble the continental crust produced in modern subduction settings3 In the East Pilbara Terrane, Western Australia, low-magnesium basalts of the Coucal Formation at the base of the Pilbara Supergroup have trace-element compositions that are consistent with these being source rocks for TTGs These basalts may be the remnants of a thick (more than 35 kilometres thick), ancient (more than 35 billion years old) basaltic crust4,5 that is predicted to have existed if Archaean mantle temperatures were much hotter than today’s6,7,8 Here, using phase equilibria modelling of the Coucal basalts, we confirm their suitability as TTG ‘parents’, and suggest that TTGs were produced by around 20 per cent to 30 per cent melting of the Coucal basalts along high geothermal gradients (of more than 700 degrees Celsius per gigapascal) We also analyse the trace-element composition of the Coucal basalts, and propose that these rocks were themselves derived from an earlier generation of high-magnesium basaltic rocks, suggesting that the arc-like signature in Archaean TTGs was inherited from an ancestral source lineage This protracted, multistage process for the production and stabilization of the first continents—coupled with the high geothermal gradients—is incompatible with modern-style plate tectonics, and favours instead the formation of TTGs near the base of thick, plateau-like basaltic crust9 Thus subduction was not required to produce TTGs in the early Archaean eonread more
Citations
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Book ChapterDOI
Paleoarchean (3.6–3.2 Ga) Mineral Systems in the Context of Continental Crust Building and the Role of Mantle Plumes
Franco Pirajno,David L. Huston +1 more
Journal ArticleDOI
A silicon memory of subduction
TL;DR: In this article, the authors used the heavy silicon isotope compositions of Archaean igneous rocks to show that the silicon that precipitated out of the Archaean oceans as chert was subducted and melted to yield seawaterlike heavy isotope signatures in early granitic rocks.
Dissertation
Petrochronology of detrital accessory phases & implications for the evolution of the Capricorn Orogen (Western Australia)
TL;DR: In this paper, acknowledgements VII chapter is given for the work of this paper. But this work is limited to two sentences: 1.II Acknowledgements 7.1
Journal ArticleDOI
Petrogenesis and tectonic implications of the ca. 2.5 Ga granitoid assemblage in the eastern Zhongtiao region, southern North China Craton
TL;DR: In this article, the authors report new petrological, mineralogical, and geochemical data for the Huping and Luojiahe trondhjemites, which are ca. 2.5 Ga granitoid assemblages from the eastern Zhongtiao region of the southern NCC.
Book ChapterDOI
The origin of magma on planetary bodies
TL;DR: The secondary crust of planetary bodies is largely basaltic, but varies from body to body depending on the makeup of the planet's mantle and its thermal history as discussed by the authors , and it can produce low-density, silicic magmatic rocks.
References
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Chemical and isotopic systematics of oceanic basalt : implications for mantle composition and processes
TL;DR: In this article, trace-element data for mid-ocean ridge basalts and ocean island basalts are used to formulate chemical systematics for oceanic basalts, interpreted in terms of partial-melting conditions, variations in residual mineralogy, involvement of subducted sediment, recycling of oceanic lithosphere and processes within the low velocity zone.
Journal ArticleDOI
Dehydration melting of metabasalt at 8-32 kbar : Implications for continental growth and crust-mantle recycling
Robert P. Rapp,E. Bruce Watson +1 more
Journal ArticleDOI
Partial melt distributions from inversion of rare earth element concentrations
Dan McKenzie,R.K. O'Nions +1 more
Journal ArticleDOI
An improved and extended internally consistent thermodynamic dataset for phases of petrological interest, involving a new equation of state for solids
Tim Holland,Roger Powell +1 more
TL;DR: In this paper, the Tait equation of state (TEOS) was used to model the temperature dependence of both the thermal expansion and bulk modulus in a consistent way, which has led to improved fitting of the phase equilibrium experiments.
Journal ArticleDOI
An internally consistent dataset with uncertainties and correlations: 3. Applications to geobarometry, worked examples and a computer program
TL;DR: In this paper, a Pascal computer program, thermocalc, is described for various thermodynamic calculations using the thermodynamic dataset presented in earlier papers in this series (Holland & Powell, 1985; Powell & Holland, 1985).