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Cobden L, Zhuang J, Lei W, Wentzcovitch R, Trampert J, Tromp J. Full-waveform tomography reveals iron spin crossover in Earth's lower mantle. Nat Commun 2024; 15:1961. [PMID: 38438365 PMCID: PMC10912123 DOI: 10.1038/s41467-024-46040-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2023] [Accepted: 02/12/2024] [Indexed: 03/06/2024] Open
Abstract
Three-dimensional models of Earth's seismic structure can be used to identify temperature-dependent phenomena, including mineralogical phase and spin transformations, that are obscured in 1-D spherical averages. Full-waveform tomography maps seismic wave-speeds inside the Earth in three dimensions, at a higher resolution than classical methods. By providing absolute wave speeds (rather than perturbations) and simultaneously constraining bulk and shear wave speeds over the same frequency range, it becomes feasible to distinguish variations in temperature from changes in composition or spin state. We present a quantitative joint interpretation of bulk and shear wave speeds in the lower mantle, using a recently published full-waveform tomography model. At all depths the diversity of wave speeds cannot be explained by an isochemical mantle. Between 1000 and 2500 km depth, hypothetical mantle models containing an electronic spin crossover in ferropericlase provide a significantly better fit to the wave-speed distributions, as well as more realistic temperatures and silica contents, than models without a spin crossover. Below 2500 km, wave speed distributions are explained by an enrichment in silica towards the core-mantle boundary. This silica enrichment may represent the fractionated remains of an ancient basal magma ocean.
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Affiliation(s)
- Laura Cobden
- Department of Earth Sciences, Utrecht University, 3584 CB Utrecht, Utrecht, The Netherlands.
| | - Jingyi Zhuang
- Department of Earth and Environmental Sciences, Columbia University, New York, NY, 10027, USA
| | - Wenjie Lei
- Department of Earth and Environmental Sciences, Columbia University, New York, NY, 10027, USA
- Department of Geosciences, Princeton University, Princeton, NJ, 08544, USA
- Google Inc., Mountain View, CA, USA
| | - Renata Wentzcovitch
- Department of Earth and Environmental Sciences, Columbia University, New York, NY, 10027, USA.
- Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY, 10027, USA.
- Lamont Doherty Earth Observatory, Palisades, NY, 10964, USA.
- Data Science Institute, Columbia University, New York, NY, 10027, USA.
- Center for Computational Quantum Physics, Flatiron Institute, New York, NY, 10010, USA.
| | - Jeannot Trampert
- Department of Earth Sciences, Utrecht University, 3584 CB Utrecht, Utrecht, The Netherlands
| | - Jeroen Tromp
- Department of Geosciences, Princeton University, Princeton, NJ, 08544, USA
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Mantle upwelling beneath the Apennines identified by receiver function imaging. Sci Rep 2020; 10:19760. [PMID: 33184406 PMCID: PMC7661539 DOI: 10.1038/s41598-020-76515-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2020] [Accepted: 10/14/2020] [Indexed: 11/22/2022] Open
Abstract
Magmatism, uplift and extension diffusely take place along collisional belts. Even though links between mantle dynamics and shallow deformation are becoming more evident, there is still poor understanding of how deep and surface processes are connected. In this work, we present new observations on the structure of the uppermost mantle beneath the Apennines belt. Receiver functions and seismic tomography consistently define a broad zone in the shallow mantle beneath the mountain belt where the shear wave velocities are lower than about 5% and the Vp/Vs ratio is higher than 3% than the reference values for these depths. We interpret these anomalies as a pronounced mantle upwelling with accumulation of melts at the crust-mantle interface, on top of which extensional seismicity responds to the crustal bending. The melted region extends from the Tyrrhenian side to the central part of the belt, with upraise of fluids within the crust favored by the current extension concentrated in the Apennines mountain range. More in general, mantle upwelling, following detachment of continental lithosphere, is a likely cause for elevated topography, magmatism and extension in post-collisional belts.
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Seismic evidence for partial melt below tectonic plates. Nature 2020; 586:555-559. [PMID: 33087914 DOI: 10.1038/s41586-020-2809-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2019] [Accepted: 08/18/2020] [Indexed: 11/08/2022]
Abstract
The seismic low-velocity zone (LVZ) of the upper mantle is generally associated with a low-viscosity asthenosphere that has a key role in decoupling tectonic plates from the mantle1. However, the origin of the LVZ remains unclear. Some studies attribute its low seismic velocities to a small amount of partial melt of minerals in the mantle2,3, whereas others attribute them to solid-state mechanisms near the solidus4-6 or the effect of its volatile contents6. Observations of shear attenuation provide additional constraints on the origin of the LVZ7. On the basis of the interpretation of global three-dimensional shear attenuation and velocity models, here we report partial melt occurring within the LVZ. We observe that partial melting down to 150-200 kilometres beneath mid-ocean ridges, major hotspots and back-arc regions feeds the asthenosphere. A small part of this melt (less than 0.30 per cent) remains trapped within the oceanic LVZ. Melt is mostly absent under continental regions. The amount of melt increases with plate velocity, increasing substantially for plate velocities of between 3 centimetres per year and 5 centimetres per year. This finding is consistent with previous observations of mantle crystal alignment underneath tectonic plates8. Our observations suggest that by reducing viscosity9 melt facilitates plate motion and large-scale crystal alignment in the asthenosphere.
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Melt mapped inside Earth’s mantle. Nature 2020; 586:506-507. [DOI: 10.1038/d41586-020-02925-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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