Constraining Upper Mantle Viscosity Using Temperature and Water Content Inferred From Seismic and Magnetotelluric Data

Ramirez, Florence; Selway, Kate; Conrad, Clinton P.; Lithgow‐Bertelloni, Carolina

doi:10.1029/2021jb023824

Cited by 6 publications

(4 citation statements)

References 97 publications

(188 reference statements)

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“…However, grounding line positions, and thus stability, of these glaciers are affected by solid earth uplift due to ice thinning. West Antarctica is characterized by low upper mantle viscosities (although absolute mantle viscosity is still poorly constrained and could benefit from an inversion using a variety of geophysical data (Ramirez et al., 2022)), and large ice mass loss (The IMBIE Team, 2018); a combination that may help to stabilize the ice sheet.…”

Section: Discussionmentioning

confidence: 99%

Solid Earth Uplift Due To Contemporary Ice Melt Above Low‐Viscosity Regions of the Upper Mantle

Weerdesteijn

Conrad

Naliboff

2022

Geophysical Research Letters

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Glacial isostatic adjustment (GIA) is the ongoing response of the solid earth and the geoid to changes in ice and ocean loading, and produces solid earth ground motion that can be measured using GNSS (Global Navigation Satellite Systems). Near areas of past or current ice cover change, it is commonly thought GIA displacements result from a combination of (a) a viscous response to historic ice load changes (i.e., ice age melting), and (b) an elastic response to contemporary ice load changes. Typically, the viscous response occurs over several thousand years, but recent studies have shown regions undergoing rapid viscous uplift on decadal or centennial timescales in response to contemporary ice melt in West Antarctica (Barletta et al., 2018;Nield et al., 2014) and southeast Greenland (Khan et al., 2016). Rapid uplift in these regions is commonly linked to low-viscosities in the upper mantle that accelerate the viscous response to recent melting. In this case, contemporary ice melt generates not only an instantaneous elastic response, but also a viscous response on short timescales. This rapid viscous response is mixed with the other deformation components of GIA (elastic and long-term viscous) that are measured using GNSS, which makes it difficult to distinguish between solid earth deformation due to historical and contemporary ice load changes (Whitehouse, 2018).There are indications that low-viscosity regions of the upper mantle are present beneath both Antarctica and Greenland. Here, we define low-viscosity regions as regions where the viscosity is considerably lower than surrounding mantle material, with a value that can result in deformation on decadal or centennial timescales (e.g., 5 ⋅ 10 19 Pa s or lower), as opposed to thousands of years. Seismic studies in Antarctica show slower velocity anomalies in West compared to East Antarctica (Heeszel et al., 2016;Lloyd et al., 2020), consistent with a colder cratonic region in East Antarctica, and a warmer tectonically active region in West Antarctica, possibly with a mantle plume (Bredow et al., 2021). Lateral variations in mantle temperature, derived from seismic velocity anomalies, suggest lateral variations in mantle rheology (Ivins & Sammis, 1995; van der Wal et al., 2013). Upper

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Section: Discussionmentioning

confidence: 99%

Solid Earth Uplift Due To Contemporary Ice Melt Above Low‐Viscosity Regions of the Upper Mantle

Weerdesteijn

Conrad

Naliboff

2022

Geophysical Research Letters

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“…If the Lehmann is due to an abrupt change in the volume of either melting or dehydration, it could also be associated with an abrupt vertical change in the electrical resistivity. Resistivity anomalies resolved in magnetotelluric studies of the uppermost mantle, however, are primarily marked by a sharp increase near 100–150 km rather than 220–240 km (Moorkamp, 2022; Ramirez et al., 2022).…”

Section: Resultsmentioning

confidence: 99%

Mantle Phase Changes Detected From Stochastic Tomography

et al. 2023

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Introduction Observed and Predicted Phase ChangesThe best-known solid phase changes in Earth's silicate mantle are commonly detected from the reflection and conversion of body waves interacting with sharp, near discontinuous, changes in velocity and density occurring at or near 410 and 660 km depth (e.g., Niu et al., 2005;Shearer, 1991). These phase changes also produce multi-pathed body waveforms between 15° and 35° great circle range (e.g., Burdick & Helmberger, 1978;Chu et al., 2012). The steepness of the inferred P and S velocity gradients between 410 and 660 km in reference Earth models, however, cannot be explained by plausible silicate mantle chemistry without the existence of at least one more phase change between 410 and 660 km (Anderson, 1989). When the tools of mineral physics are applied to a constrained composition of the Earth's mantle, up to two additional phase changes are predicted to occur between the 410 and 660 km. Several other phase changes are also predicted above and below this zone, each having a unique behavior in their Clapeyron slope and the widths in depth over which each occurs (Figure 1). The widths of more than half of these are on the order of 15-60 km (e.g., Stixrude & Lithgow-Bertelloni, 2007, 2011, some expressed primarily by changes in velocity gradient, making them difficult to detect from reflected and converted body waves having similar or shorter wavelengths. As demonstrated in Figure 1, the parameterization Abstract Stochastic tomography, made possible by dense deployments of seismic sensors, is used to identify phase changes in Earth's mantle that occur over depth intervals. This technique inverts spatial coherences of amplitudes and travel times of body waves to determine the depth and dependence of the spatial spectrum of seismic velocity. This spectrum is interpreted using the predicted thermodynamic stability of mineral composition and phase as a function of temperature and pressure, in which the metamorphic temperature derivative of seismic velocities is used as a proxy for the effects of heterogeneity induced in a region undergoing a phase change. Peaks in the temperature derivative of seismic velocity closely match those found from applying stochastic tomography to elements of Earthscope and Flex arrays. Within ±12 km, peaks in the fluctuation of P velocity at 425, 500, and 600 km depth beneath the western US agree with those predicted by a mechanical mixture of harzburgite and basalt, 180 K cooler than a 1600 K adiabat in the mantle transition zone. A broad peak at 250 km depth may be associated with chemical heterogeneity induced by dehydration of subducted oceanic sediments, and a peak at 775 km depth with a phase change in subducted basalt. Non-detection of predicted phase changes less than 10 km in width is consistent with the resolution possible with the seismic arrays used in the inversion, including the sharp endothermic phase change near 660 km. These interpretations are consistent with the known history of plate subduction beneath North America.

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“…Since water content in olivine is one of the major controls on mantle rheology (e.g., Hirth & Kohlstedf, 2003), higher water contents in the cratonic mantle should, all else being equal, make it weaker than the Eastern Branch lithospheric mantle. Selway (2015) suggested that small grain sizes in the Eastern Branch lithosphere, which may still remain as a scar from Pan‐African deformation, could contribute to weakening the Eastern Branch lithosphere and could outweigh the impact of water content (e.g., Ramirez et al., 2022). Mantle xenoliths from the volcanoes along the rift zone (Pello Hill and Elodoi) do indeed dominantly have porphyroclastic textures with smaller olivine grain sizes (0.4–2 mm Baptiste et al., 2015).…”

Section: Electrical Structure Metasomatism and Volcanism In Northern ...mentioning

confidence: 99%

Role of Metasomatism in the Development of the East African Rift at the Northern Tanzanian Divergence: Insights From 3D Magnetotelluric Modeling

Özaydın,

Selway,

Foley

et al. 2024

Geochem Geophys Geosyst

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The Northern Tanzanian Divergence in the East Africa Rift is arguably the best place on Earth to study the controls on rifting of thick lithosphere. Here, where the East Africa Rift intersects the Tanzanian Craton and the Mozambique Belt, the relationships between volcanism, faulting, pre‐existing structures and lithospheric thickness and composition can be observed. In this work, we carry out the first lithospheric‐scale 3D magnetotelluric modeling of the Northern Tanzanian Divergence and combine the results with experimental electrical conductivity and petrology models to calculate mantle composition, which is also inferred in the craton from reanalysis of garnet xenocryst data. Our results show that metasomatic materials exist in the cratonic lithospheric mantle and the relatively undeveloped southern part of the rift zone. However, the lithospheric mantle of the Mozambique Belt and the more developed northern section of the rift is more resistive and does not contain metasomatic phases. Combined with geochemical data from erupted lavas, these results suggest that, in zones that have experienced voluminous Cenozoic magmatism, melting events have destroyed the metasomes and dehydrated the mantle. Since the presence of magma is a primary control of lithospheric strength, rifting may become limited as the lithospheric mantle becomes dehydrated and harder to melt.

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Constraining Upper Mantle Viscosity Using Temperature and Water Content Inferred From Seismic and Magnetotelluric Data

Cited by 6 publications

References 97 publications

Solid Earth Uplift Due To Contemporary Ice Melt Above Low‐Viscosity Regions of the Upper Mantle

Solid Earth Uplift Due To Contemporary Ice Melt Above Low‐Viscosity Regions of the Upper Mantle

Mantle Phase Changes Detected From Stochastic Tomography

Role of Metasomatism in the Development of the East African Rift at the Northern Tanzanian Divergence: Insights From 3D Magnetotelluric Modeling

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