The persistent myth of crustal growth

Armstrong, R. L.

doi:10.1080/08120099108727995

Cited by 305 publications

(115 citation statements)

References 146 publications

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“…(2) The full amount of CC developed at the beginning and has been recycled again and again [Armstrong, 1991]. We could supplement this view by the following question.…”

Section: General Discussion and Conclusionmentioning

confidence: 99%

Mantle convection and evolution with growing continents

Walzer

Hendel

2008

J. Geophys. Res.

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[1] We present a three-dimensional spherical shell numerical model for chemical differentiation and redistribution of incompatible elements in a convective Earth's mantle heated mostly from within by U, Th, and K and slightly from below. The evolution-model equations guarantee conservation of mass, momentum, energy, angular momentum, and four sums of the number of atoms of the pairs 238 U-206 Pb, 235 U-207 Pb, 232 Th-208 Pb, and 40 K-40 Ar. The pressure-and temperature-dependent viscosity is supplemented by a viscoplastic yield stress, s y . The lithospheric viscosity is partly imposed to mimic its increase by dehydration of oceanic lithosphere and other effects. Also, the asthenosphere is generated not only by the distribution of temperature and melting temperature, but essentially by the profiles of water solubility and water abundance. Therefore we introduced a radial viscosity profile factor describing that behavior. However, the focus of this paper is the episodic growth of continents and oceanic plateaus. As a complement, the differentiation generates the depleted MORB mantle (DMM) which predominates immediately beneath the lithosphere. Our continents are not artificially imposed on the surface of the spherical shell, but instead they evolve by the interplay between chemical differentiation and convection/mixing. No restrictions are imposed regarding number, size, form, and distribution of continents. However, oceanic plateaus that impinge upon a continent have to be united with it. This mimics the accretion of terranes. The numerical results show an episodic growth of the total mass of the continents and display a plausible time history for the laterally averaged surface heat flow, qob, and the Rayleigh number, Ra. We use our model to explore a moderate region of Ra-s y parameter space. We find Earth-like continent distributions in a central part of the Ra-s y space we explored. We identified a Ra-s y region where the calculated total continental volume is very close to the observed value; another Ra-s y region where the Urey number, Ur, is close to the accepted value; a third Ra-s y area where surface heat flow is very close to the present-day observed mean global heat flow using typical abundances of the heat-producing elements. It is remarkable that these different acceptable Ra-s y regions share a common overlap area, where Earth-like behavior is simultaneously fulfilled.Although the convective flow patterns and the chemical differentiation of oceanic plateaus are coupled, the evolution of time-dependent Rayleigh number, Ra t , is relatively well predictable and the stochastic parts of the Ra t (t) curves are small. Regarding the time distribution of juvenile growth rates of the total mass of the continents, predictions are possible only in the first epoch of the evolution, presumed that the initial conditions are given. Later on, the distribution of the continental growth episodes is increasingly stochastic. Independent of the varying individual runs, our model shows that the total mass of the presen...

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“…(2) The full amount of CC developed at the beginning and has been recycled again and again [Armstrong, 1991]. We could supplement this view by the following question.…”

Section: General Discussion and Conclusionmentioning

confidence: 99%

Mantle convection and evolution with growing continents

Walzer

Hendel

2008

J. Geophys. Res.

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“…How long are anatexic events and how does the duration of one depend on the rate of supply of enthalpy? In this paper we address some of these issues using a fluid dynamical model previously developed [Oldenburg and Spera, 1990, 1991, 1992a, 1992bSpera et al, 1995]. A cartoon of the scenario investigated is shown in Figure 1; boundary and initial conditions are portrayed in Figure 2.…”

Section: Crustal Anatexismentioning

confidence: 99%

Simulations of crustal anatexis: Implications for the growth and differentiation of continental crust

Raia¹,

Spera²

1997

J. Geophys. Res.

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Abstract. Them is overwhelming and incontrovertible petrological and geophysical evidence for the significant role played by mantle-derived mafic magma in the generation and growth of continental crust. Likewise, intrusion of mafic magmas beneath or into continental crust is very likely the major source of enthalpy that drives intracrustal differentiation. A simple dynamical model has been constructed to examine the critical factors that govern the evolution and timescale of crustal anatexic events when driven by basaltic magma underplating or injection into crust. Critical factors include the intensity of the enthalpy input (i.e., the power dissipated) and the rheological propertie.s, bulk composition and compositional structure of the source rocks undergoing partial fusion. We have performed numerical simulations to evaluate these factors using phase equilibria and thermochemical and transport property data applicable to the binary eutectic system CaA12Si2Oa-CaMgSi20 6 as a rough analog to study anatexis of mafic lower crust. In distinction, forfscrit small, more enthalpy is stored in the solid and less melt is produced. However, the compositional spectrum of liquids generated within the anatexic region is significantly larger for smallfscrit. Because of the sensitive dependence of solidi and liquidi on bulk composition, melt productivity is related to bulk composition given a particular enthalpy power input and rheological model. There is a factor of 2 difference in volume of melt generated when the bulk composition of the source is 10 modal percent less refractory. Compositionally zoned melts form by melting of either homogeneous or layered sources, although compositionfrequency relations are sensitive to the initial (subsolidus) compositional structure. The effects of anatexic events are to fundamentally reorganize the pattern of compositional structure within the crust. Intracrustal differentiation is a long-term inevitable process associated with the underplating or injection of mafic magma into preexisting crust.

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“…Most Earth scientists assume that continental crust volume has been growing over Earth history (see review and critique by Armstrong 1991), but when the question 'has continental crust volume increased or decreased with time?' is addressed thoughtfully, it must be admitted that there is much that is not known.…”

Section: Introductionmentioning

confidence: 99%

Yin and yang of continental crust creation and destruction by plate tectonic processes

Stern

Scholl

2010

International Geology Review

200

107

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Earth's continental crust today is both created and destroyed by plate tectonic processes, a balance that is encapsulated by the traditional Chinese concept of yin-yang, whereby dualities act in concert as well as in opposition. Yin-yang conceptualizations of crustal growth and destruction are mostly related to plate tectonics; both occur mostly at subduction zones, by arc magmatic creation and by subduction removal. Crust is also created and destroyed by processes unrelated to plate tectonics, including losses by lower crust foundering and additions at hotspots. At present, creation and destruction of continental crust is either in balance (∼3.2 km 3 /year, or 3.2 AU) or more crust is being destroyed than created; the uncertainty comes from unknown deep losses of continental crust at collision zones and due to lower crustal foundering. The yinyang creation-destruction balance changes over a supercontinent cycle, with crustal growth being greatest during supercontinent break-up due to high magmatic flux at new arcs and crustal destruction being greatest during supercontinent amalgamation due to subduction of continental material and increased sediment flux due to orogenic uplift. These conclusions challenge the widely held view that continental crust volume has increased over time due to plate tectonic activity; it is just as likely that this volume has decreased.

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The persistent myth of crustal growth

Cited by 305 publications

References 146 publications

Mantle convection and evolution with growing continents

Mantle convection and evolution with growing continents

Simulations of crustal anatexis: Implications for the growth and differentiation of continental crust

Yin and yang of continental crust creation and destruction by plate tectonic processes

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