Strong plates enhance mantle mixing in early Earth

Agrusta, Roberto; Hunen, Jeroen van; Goes, Saskia

doi:10.1038/s41467-018-05194-5

Cited by 25 publications

(12 citation statements)

References 69 publications

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“…Numerical models also appear to resolve supposed conflicts between whole-mantle convection and a mantle with geochemical and seismic heterogeneity (Jordan et al 1993;Schuberth et al 2009;Barry et al 2018). So while controversy still exists over seismic images of deep-seated plumes (e.g., Montelli et al 2004), we agree with recent Agrusta et al (2018), that Earth's mantle has long been well stirred. But if all these studies are in error, Table 2 provides estimates for lower mantle composition, for three cases: that h exists below 1,850 km (a minimum volume), 1,000 km and 660 km.…”

Section: Does Earth Have a Hidden Mantle Component Or A Compositionalsupporting

confidence: 73%

The composition and mineralogy of rocky exoplanets: A survey of >4000 stars from the Hypatia Catalog

Putirka

Rarick

2019

American Mineralogist

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We present a survey of >4,000 star compositions from the Hypatia Catalog to examine whether rocky exoplanets (i.e., those with rocky surfaces, dominated by silicates) might be geologically similar to Earth, at least with respect to composition and mineralogy. To do so, we explore the variety of reported stellar compositions to then determine a possible range of exoplanetary mantle mineralogies. We find that exoplanetary mantles will likely be dominated by olivine and/or orthopyroxene, depending upon Fe partitioning during core formation. Some exoplanets may be magnesiowüstite-or quartz-saturated, and we present a new classification scheme based on the weight % ratio (FeO+MgO)/SiO2, to differentiate rock types. But wholly exotic mineralogies should be rare to absent. We find that half or more of the range of exoplanet mantle mineralogy is controlled by core formation, which we model using Fe = Fe BSP /Fe BP , where Fe BSP is Fe in a Bulk Silicate Planet (bulk planet, minus core), on a cation weight % basis (elemental weight proportions, absent anions) and Fe BP is the cation weight % of Fe for a Bulk Planet. In our solar system, Fe varies from 0 (Mercury) to about 0.54 (Mars)]. Remaining variations in exoplanet mantle mineralogy result from non-trivial variations in star compositions. But we also find that Earth is decidedly non-solar (non-chondritic); this is not a new result, but appears worth re-emphasizing, given that current discussions often still use carbonaceous or enstatite chondrites as models of bulk Earth. We conclude that such models are untenable, regardless of the close overlap of some isotope ratios between certain meteoritic and terrestrial (Earth-derived) samples. There is also the possibility that Earth contains a hidden component, that if added to known reservoirs would yield a solar/chondritic Earth. We test that idea using a mass balance of major oxides using known reservoirs, so that the sum of upper mantle, metallic core and crust, plus a hidden component, yield a solar bulk composition. Here, the fractions of crust and core are fixed and the hidden mantle component is some unknown fraction of the entire mantle, Fh (so if FDM is the fraction of depleted mantle, then Fh + FDM = 1). Such mass balance shows that if a hidden mantle component were to exist, it must comprise >28% of Earth's mantle, otherwise it would have negative major oxide abundances. There is no clear upper limit for such a component, so it could comprise the entire mantle, but all estimates from Fh = 0.28 to Fh = 1.0 yield a hidden fraction that does not match the sources of mantle plumes or midocean ridge basalt (MORB). The putative component is also geologically unusual, being enriched in Na and Fe, and depleted in Ca and Mg, compared to familiar mantle components. We conclude that such a hidden component does not exist.

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Section: Does Earth Have a Hidden Mantle Component Or A Compositionalsupporting

confidence: 73%

The composition and mineralogy of rocky exoplanets: A survey of >4000 stars from the Hypatia Catalog

Putirka

Rarick

2019

American Mineralogist

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“…with t end , the final time of the simulations. D is similar to the parameter defined by Agrusta et al (2018), and it indicates whether the slab is more prone to sink in the lower mantle or to get trapped in the MTZ. A slab that does not accumulate into the MTZ will have both t fold and D less than 1.…”

Section: Investigated Parametersmentioning

confidence: 96%

“…Indeed, Sigloch and Mihalynuk (2013) suggest that the thick lower mantle anomalies below North America may be indicators of a remnant slab that piled up almost vertically near the MTZ before breaking and sinking into the lower mantle. Slab buckling and folding may be induced by strong slab pull forces linked to the 410-km discontinuity (i.e., olivine to wadsleyite [ol-wd] transition) and by a strong barrier to slab penetration due to the post-spinel phase transition (Běhounková & Čížková, 2008), by the reduction of the thermal expansivity with depth (Tosi et al, 2015), or by the deformation of young and weak subducting plates (Agrusta et al, 2018;Garel et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

Topographic Fingerprint of Deep Mantle Subduction

et al. 2020

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The dynamic topography links with the mantle structures at various temporal and spatial scales. However, it is still unclear how it relates to the dynamics of subducting lithosphere when plates reach the mantle transition zone and lower mantle. Seismic tomography images show how slab morphologies vary from sinking subvertically into the lower mantle, to lying flat above the upper-lower mantle discontinuity, to thickening in the shallow lower mantle. These slab shapes have been considered to be the result of variable interaction of the slab with the upper-lower mantle discontinuity at~670 km depth. Previous studies show that periodic deep slab dynamics can explain a variety of enigmatic geological and geophysical observations such as periodic variations of the plate velocities, trench retreat and advance episodes, and the scattered distribution of slab dip angle in the upper mantle. In this study, we use two-dimensional subduction models to investigate the surface topography expression and its evolution during slab transition zone interaction. Our models show that topography does not depend on slab morphology; indeed, the dynamic topography cannot distinguish between a slab sinking straight into the lower mantle and slab stagnation at the upper-lower mantle boundary. However, topographic oscillations are related to episodes of the trench advance and retreat, which in turn are linked to the slab folding behavior at transition zone depths. Our results suggest that the surface transient signal observed by geological studies could help to detect deep subduction dynamics.

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“…A further alternative is that plate subduction did take place in the Archean, but without significant trench retreat and hence without the spreading events that preceded the post-2 Ga boninitic protoarcs. It is possible, for example, that weaker Archean asthenosphere and lower plate density and strength favored deep penetration of slabs into the mantle but inhibited trench retreat (Agrusta et al, 2018). In that case, there would be no reservoir of hot, residual (harzburgitic) mantle trapped in the embryonic mantle wedge and hence no newly depleted source available to form a boninitic protoarc ( Fig.…”

Section: -2 Ga: Principal Period Of Izu-bonin-mariana-type Subductiomentioning

confidence: 99%

Identification, classification, and interpretation of boninites from Anthropocene to Eoarchean using Si-Mg-Ti systematics

2019

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Boninites are rare, high-Si, high-Mg, low-Ti lavas that have considerable tectonic significance, especially for recognizing and interpreting episodes of subduction initiation in the geologic record. Formal identification and classification of boninites may be carried out using MgO-SiO2 and MgO-TiO2 diagrams to find compositions that satisfy modified International Union of Geological Sciences (IUGS) criteria of Si8 > 52 and Ti8 < 0.5, where Si8 and Ti8 refer to concentrations of the oxides at 8 wt% MgO. However, screening of highly metasomatized rocks and accurate classification require precautions, including normalization to a 100% volatile-free basis. The MgO-SiO2 diagram can also be used for subdivision into low-Si boninites (Si8 < 57) and high-Si boninites (Si8 > 57). Satisfying one but not both of the boninite criteria are rocks with Si8 > 52 but Ti8 ≥ 0.5 (siliceous high-magnesium basalts) and rocks with Si8 ≤ 52 but Ti8 < 0.5 (low-Ti basalts). We tested the classification methodologies using ∼100 low-Ti lava suites dating from the present-day back to the Eoarchean. We conclude that, of those classifying as “boninite series,” Izu-Bonin-Mariana arc–type subduction initiation terranes provide the dominant setting only back as far as ca. 2 Ga, which marks the maximum age of extensive clinopyroxene-undersaturated melting and eruption of high-Si boninites. From 2 to 3 Ga, most boninites formed in intraplate settings by melting of refertilized, depleted cratonic roots. Prior to 3 Ga, hot, depleted mantle plumes provided the main boninite sources. Nonetheless, arc-basin boninites, though rare, do extend back to 3.8 Ga, and, together with the inherited subduction component in intracratonic boninites, they provide evidence for some form of subduction during the Archean.

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Strong plates enhance mantle mixing in early Earth

Cited by 25 publications

References 69 publications

The composition and mineralogy of rocky exoplanets: A survey of >4000 stars from the Hypatia Catalog

The composition and mineralogy of rocky exoplanets: A survey of >4000 stars from the Hypatia Catalog

Topographic Fingerprint of Deep Mantle Subduction

Identification, classification, and interpretation of boninites from Anthropocene to Eoarchean using Si-Mg-Ti systematics

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