Seismic evidence for depth-dependent metasomatism in cratons

Eeken, Thomas; Goes, Saskia; Pedersen, Helle A.; Arndt, Nicholas; Bouilhol, Pierre

doi:10.1016/j.epsl.2018.03.018

Cited by 47 publications

(79 citation statements)

References 98 publications

(132 reference statements)

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“…Considering the sum of our results, we suggest that a combination of ≤20 vol.% eclogite with~2 vol.% diamond is the most consistent solution arising from all constraints described here. It has been suggested elsewhere that cratonic V s may be matched by highly depleted peridotites (e.g., harzburgites or dunites: Afonso et al, 2008;Eeken et al, 2018); though these bulk compositions yield faster V s than compositionally average cratonic peridotites, our calculations show that they do not achieve the seismically observed craton average V s . Further, even if forward-modeled V s for such highly depleted peridotites were to match the craton average V s , it would require that cratonic lithosphere was composed solely of the end-member, most-depleted lithologies, in contrast to the compositional diversity observed in cratonic xenolith suites (e.g., Griffin et al, 2002).…”

Section: 1029/2018gc007534contrasting

confidence: 70%

“…Many studies have modeled geophysical observations of cratons to understand their compositional and thermal structure (e.g., Afonso et al, 2008;Dalton et al, 2017;Eeken et al, 2018;Hieronymus & Goes, 2010;Hirsch et al, 2015;Jones et al, 2017). These studies reveal disagreement as to how fast cratonic shear-wave velocities are in the depth range~100-170 km, and whether they can be matched by known cratonic peridotite compositions.…”

Section: Statement Of the Problemmentioning

confidence: 99%

“…For example, a recent study using the Holland and Powell (1998) thermodynamic data set yields cratonic peridotite V s~0 .05 km/s faster than the Stixrude and Lithgow-Bertelloni (2005) thermodynamic data set, even though the same shear moduli and averaging schemes (Abers & Hacker, 2016) were used for both calculated mineral assemblages (cf. Eeken et al, 2018, their Figure S2). Further, treating solid-solution end-members as separable phases (Abers & Hacker, 2016;Hacker & Abers, 2004;Hacker et al, 2003) or using Voigt averages for solution-phase shear moduli, as is done in the thermodynamic modeling software Perple_X (Afonso et al, 2008;Connolly & Kerrick, 2002), yield bulk peridotite V s that can be an additional~0.05 km/s too fast relative to thermodynamically justified Reuss averages (Stixrude & Lithgow-Bertelloni, 2005; see Text S1).…”

Section: Statement Of the Problemmentioning

confidence: 99%

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Multidisciplinary Constraints on the Abundance of Diamond and Eclogite in the Cratonic Lithosphere

Garber

Maurya

Hernandez

et al. 2018

Geochem Geophys Geosyst

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Some seismic models derived from tomographic studies indicate elevated shear‐wave velocities (≥4.7 km/s) around 120–150 km depth in cratonic lithospheric mantle. These velocities are higher than those of cratonic peridotites, even assuming a cold cratonic geotherm (i.e., 35 mW/m2 surface heat flux) and accounting for compositional heterogeneity in cratonic peridotite xenoliths and the effects of anelasticity. We reviewed various geophysical and petrologic constraints on the nature of cratonic roots (seismic velocities, lithology/mineralogy, electrical conductivity, and gravity) and explored a range of permissible rock and mineral assemblages that can explain the high seismic velocities. These constraints suggest that diamond and eclogite are the most likely high‐Vs candidates to explain the observed velocities, but matching the high shear‐wave velocities requires either a large proportion of eclogite (>50 vol.%) or the presence of up to 3 vol.% diamond, with the exact values depending on peridotite and eclogite compositions and the geotherm. Both of these estimates are higher than predicted by observations made on natural samples from kimberlites. However, a combination of ≤20 vol.% eclogite and ~2 vol.% diamond may account for high shear‐wave velocities, in proportions consistent with multiple geophysical observables, data from natural samples, and within mass balance constraints for global carbon. Our results further show that cratonic thermal structure need not be significantly cooler than determined from xenolith thermobarometry.

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Section: 1029/2018gc007534contrasting

confidence: 70%

Section: Statement Of the Problemmentioning

confidence: 99%

Section: Statement Of the Problemmentioning

confidence: 99%

See 1 more Smart Citation

Multidisciplinary Constraints on the Abundance of Diamond and Eclogite in the Cratonic Lithosphere

Garber

Maurya

Hernandez

et al. 2018

Geochem Geophys Geosyst

View full text Add to dashboard Cite

show abstract

“…At very low frequencies (very long periods, hundreds of seconds for the specified conditions), steady state creep further significantly increases attenuation and decreases the Figure 4, from the five surface wave models (Pollitz & Mooney, 2016;Porter et al, 2016;Schmandt et al, 2015;Shen & Ritzwoller, 2016;Wagner et al, 2018) and the electrical resistivity inverse solutions. Some work has taken anelasticity into account when determining seismic constraints on temperature (e.g., Armitage et al, 2015;Eeken et al, 2018;Goes et al, 2005;Yang & Forsyth, 2008). Note that there is considerable variability between models.…”

Section: Anelasticity Grain Size and Seismic Velocitymentioning

confidence: 99%

“…Though much of the current research on anelasticity has been specifically targeted at understanding the cause of midlithospheric discontinuities (MLDs; e.g., Karato et al, 2015;Selway et al, 2015) and at characterizing the nature of the LAB (e.g., Olugboji et al, 2013;Olugboji et al, 2016), the proposed models of anelastic controls on seismic observables can, and indeed should, be applied more broadly when formulating geodynamic interpretations of observed seismic anomalies. Some work has taken anelasticity into account when determining seismic constraints on temperature (e.g., Armitage et al, 2015;Eeken et al, 2018;Goes et al, 2005;Yang & Forsyth, 2008). However, all too frequently seismic velocity anomalies, expressed as percent deviations from an assumed reference model, are only qualitatively interpreted in terms of relative temperatures, with slow (fast) anomalies being translated directly into hot (cold) lithosphere or even asthenosphere.…”

Section: 1029/2019gc008279mentioning

confidence: 99%

Synthesizing Seemingly Contradictory Seismic and Magnetotelluric Observations in the Southeastern United States to Image Physical Properties of the Lithosphere

Murphy

Egbert

2019

Geochem Geophys Geosyst

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Although seismic velocity and electrical conductivity are both sensitive to temperature, thermal lithosphere properties are derived almost exclusively from seismic data because conductivity is often too strongly affected by minor highly conductive phases to be a reliable indicator of temperature. However, in certain circumstances, electrical observations can provide strong constraints on mantle temperatures. In the southeastern United States (SEUS), magnetotelluric (MT) data require high resistivity values (>300 Ωm) to at least 200‐km depth. As dry mantle mineral conduction laws provide an upper bound on temperature for an observed resistivity value, the only interpretation is that lithospheric temperatures (<1330 °C) persist to 200 km. However, seismic tomography shows that velocities in this region are generally slightly slow with respect to references models; this observation has led to a view of relatively thin (<150 km), eroded thermal lithosphere beneath the SEUS. We show that MT and seismic (tomography, attenuation, receiver function) results are consistent with thick (~200 km), coherent thermal lithosphere in this region. Reduced seismic velocities (relative to reference models) can be explained by considering the effect of finite grain size (anelasticity). Calculated velocity as a function of temperature is overall slower when including anelastic effects, even at reasonable grain sizes of 1 mm to 1 cm; this permits mantle temperatures that are colder than would typically be inferred. We argue for a geodynamic scenario in which the present thermal lithosphere in the SEUS formed in association with the Central Atlantic Magmatic Province and has subsequently survived intact for ~200 Ma.

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Geophysical evidence for crustal and mantle weak zones controlling intra-plate seismicity - the 2017 Botswana earthquake sequence

Moorkamp

Fishwick

Walker

et al. 2018

Preprint

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Large earthquakes away from plate boundaries pose a significant threat to human lives and infrastructure, but such events typically occur on previously unknown faults. Most cases of intra-plate seismicity result from compression related to far-field plate boundary stresses. The April 2017 M W 6.5 earthquake in central Botswana, and subsequent events, occurred in a region with no previously known large earthquakes, occurred away from major present day tectonic activity, and accommodate extension rather than compression. Here, we present results from an integrated geophysical study that suggests the recent earthquakes may be a sign of future activity, controlled by the collocation of a weak upper mantle and weak crustal structure, between otherwise strong Precambrian blocks. Magnetotelluric data highlights Proterozoic continent accretion structure within the region, and shows that recent extension and seismicity occurred along ancient thrust faults within the crust. Our seismic velocity and resistivity models suggest a weak zone in the uppermost mantle, that does not persist to greater depths, and is therefore unlikely to represent mantle upwelling.The Botswana events may therefore be indicative of top-down extension as a response to large scale extensional forces.

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Seismic evidence for depth-dependent metasomatism in cratons

Cited by 47 publications

References 98 publications

Multidisciplinary Constraints on the Abundance of Diamond and Eclogite in the Cratonic Lithosphere

Multidisciplinary Constraints on the Abundance of Diamond and Eclogite in the Cratonic Lithosphere

Synthesizing Seemingly Contradictory Seismic and Magnetotelluric Observations in the Southeastern United States to Image Physical Properties of the Lithosphere

Geophysical evidence for crustal and mantle weak zones controlling intra-plate seismicity - the 2017 Botswana earthquake sequence

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