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Qin Y, Singh SC, Grevemeyer I, Marjanović M, Roger Buck W. Discovery of flat seismic reflections in the mantle beneath the young Juan de Fuca Plate. Nat Commun 2020; 11:4122. [PMID: 32807778 PMCID: PMC7431579 DOI: 10.1038/s41467-020-17946-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2019] [Accepted: 07/24/2020] [Indexed: 11/28/2022] Open
Abstract
Crustal properties of young oceanic lithosphere have been examined extensively, but the nature of the mantle lithosphere underneath remains elusive. Using a novel wide-angle seismic imaging technique, here we show the presence of two sub-horizontal reflections at ∼11 and ∼14.5 km below the seafloor over the 0.51-2.67 Ma old Juan de Fuca Plate. We find that the observed reflectors originate from 300-600-m-thick layers, with an ∼7-8% drop in P-wave velocity. They could be explained either by the presence of partially molten sills or frozen gabbroic sills. If partially molten, the shallower sill would define the base of a thin lithosphere with the constant thickness (11 km), requiring the presence of a mantle thermal anomaly extending up to 2.67 Ma. In contrast, if these reflections were frozen melt sills, they would imply the presence of thick young oceanic lithosphere (20-25 km), and extremely heterogeneous upper mantle.
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Affiliation(s)
- Yanfang Qin
- Institut de Physique de Globe de Paris, 1 rue Jussieu, 75238, Paris, France
- Now at Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Showa-machi 3173-25, Kanazawa-ku, Yokohama, 236-0001, Japan
| | - Satish C Singh
- Institut de Physique de Globe de Paris, 1 rue Jussieu, 75238, Paris, France.
| | - Ingo Grevemeyer
- GEOMAR, Helmholtz Centre for Ocean Research Kiel, Wischhofstr 1-3, 24148, Kiel, Germany
| | - Milena Marjanović
- Institut de Physique de Globe de Paris, 1 rue Jussieu, 75238, Paris, France
| | - W Roger Buck
- Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY, 10964-1000, USA
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Lavayssière A, Rychert C, Harmon N, Keir D, Hammond JOS, Kendall J, Doubre C, Leroy S. Imaging Lithospheric Discontinuities Beneath the Northern East African Rift Using S-to- P Receiver Functions. GEOCHEMISTRY, GEOPHYSICS, GEOSYSTEMS : G(3) 2018; 19:4048-4062. [PMID: 30774560 PMCID: PMC6360955 DOI: 10.1029/2018gc007463] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/27/2018] [Revised: 08/21/2018] [Accepted: 08/26/2018] [Indexed: 06/09/2023]
Abstract
Imaging the lithosphere is key to understand mechanisms of extension as rifting progresses. Continental rifting results in a combination of mechanical stretching and thinning of the lithosphere, decompression upwelling, heating, sometimes partial melting of the asthenosphere, and potentially partial melting of the mantle lithosphere. The northern East African Rift system is an ideal locale to study these processes as it exposes the transition from tectonically active continental rifting to incipient seafloor spreading. Here we use S-to-P receiver functions to image the lithospheric structure beneath the northernmost East African Rift system where it forms a triple junction between the Main Ethiopian rift, the Red Sea rift, and the Gulf of Aden rift. We image the Moho at 31 ± 6 km beneath the Ethiopian plateau. The crust is 28 ± 3 km thick beneath the Main Ethiopian rift and thins to 23 ± 2 km in northern Afar. We identify a negative phase, a velocity decrease with depth, at 67 ± 3 km depth beneath the Ethiopian plateau, likely associated with the lithosphere-asthenosphere boundary (LAB), and a lack of a LAB phase beneath the rift. Using observations and waveform modeling, we show that the LAB phase beneath the plateau is likely defined by a small amount of partial melt. The lack of a LAB phase beneath the rift suggests melt percolation through the base of the lithosphere beneath the northernmost East African Rift system.
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Affiliation(s)
- Aude Lavayssière
- National Oceanography CentreUniversity of SouthamptonSouthamptonUK
| | | | - Nicholas Harmon
- National Oceanography CentreUniversity of SouthamptonSouthamptonUK
| | - Derek Keir
- National Oceanography CentreUniversity of SouthamptonSouthamptonUK
- Dipartimento di Scienze della TerraUniversità degli Studi di FirenzeFirenzeItaly
| | - James O. S. Hammond
- Department of Earth and Planetary Sciences, BirkbeckUniversity of LondonLondonUK
| | | | - Cécile Doubre
- Institut de Physique du Globe de Strasbourg, UMR 7516Université de Strasbourg/EOST, CNRSStrasbourgFrance
| | - Sylvie Leroy
- CNRS, UMR 7193, Institut des Sciences de la Terre de ParisSorbonne UniversitéParisFrance
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Chichester B, Rychert C, Harmon N, van der Lee S, Frederiksen A, Zhang H. Seismic Imaging of the North American Midcontinent Rift Using S-to- P Receiver Functions. JOURNAL OF GEOPHYSICAL RESEARCH. SOLID EARTH 2018; 123:7791-7805. [PMID: 31032165 PMCID: PMC6473666 DOI: 10.1029/2018jb015771] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/15/2018] [Revised: 08/03/2018] [Accepted: 08/17/2018] [Indexed: 06/09/2023]
Abstract
North America's ~1.1-Ga failed Midcontinent Rift (MCR) is a striking feature of gravity and magnetic anomaly maps across the continent. However, how the rift affected the underlying lithosphere is not well understood. With data from the Superior Province Rifting Earthscope Experiment and the USArray Transportable Array, we constrain three-dimensional seismic velocity discontinuity structure in the lithosphere beneath the southwestward arm of the MCR using S-to-P receiver functions. We image a velocity increase with depth associated with the Moho at depths of 33-40 ± 4 km, generally deepening toward the east. The Moho amplitude decreases beneath the rift axis in Minnesota and Wisconsin, where the velocity gradient is more gradual, possibly due to crustal underplating. We see hints of a deeper velocity increase at 61 ± 4-km depth that may be the base of underplating. Beneath the rift axis further south in Iowa, we image two distinct positive phases at 34-39 ± 4 and 62-65 ± 4 km likely related to an altered Moho and an underplated layer. We image velocity decreases with depth at depths of 90-190 ± 7 km in some locations that do not geographically correlate with the rift. These include a discontinuity at depths of 90-120 ± 7 km with a northerly dip in the south that abruptly deepens to 150-190 ± 7 km across the Spirit Lake Tectonic Zone provincial suture. The negative phases may represent a patchy, frozen-in midlithosphere discontinuity feature that likely predates the MCR and/or be related to lithospheric thickness.
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Affiliation(s)
- Ben Chichester
- National Oceanography Centre Southampton, Ocean and Earth SciencesUniversity of SouthamptonSouthamptonUK
| | - Catherine Rychert
- National Oceanography Centre Southampton, Ocean and Earth SciencesUniversity of SouthamptonSouthamptonUK
| | - Nicholas Harmon
- National Oceanography Centre Southampton, Ocean and Earth SciencesUniversity of SouthamptonSouthamptonUK
| | - Suzan van der Lee
- Department of Earth and Planetary SciencesNorthwestern UniversityEvanstonILUSA
| | - Andrew Frederiksen
- Department of Geological SciencesUniversity of ManitobaWinnipegManitobaCanada
| | - Hao Zhang
- Department of Geology and GeophysicsUniversity of UtahSalt Lake CityUTUSA
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Rychert CA, Harmon N. Predictions and Observations for the Oceanic Lithosphere From S-to- P Receiver Functions and SS Precursors. GEOPHYSICAL RESEARCH LETTERS 2018; 45:5398-5406. [PMID: 30034045 PMCID: PMC6049891 DOI: 10.1029/2018gl077675] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/23/2018] [Revised: 05/02/2018] [Accepted: 05/09/2018] [Indexed: 06/08/2023]
Abstract
The ocean lithosphere is classically described by the thermal half-space cooling (HSC) or the plate models, both characterized by a gradual transition to the asthenosphere beneath. Scattered waves find sharp seismic discontinuities beneath the oceans, possibly from the base of the plate. Active source studies suggest sharp discontinuities from a melt channel. We calculate synthetic S-to-P receiver functions and SS precursors for the HSC and plate models and also for channels. We find that the HSC and plate model velocity gradients are too gradual to create interpretable scattered waves from the base of the plate. Subtle phases are predicted to follow a similar trend as observations, flattening at older ages. Therefore, the seismic discontinuities are probably caused by a thermally controlled process that can also explain their amplitude, such as melting. Melt may coalesce in channels, although channels >10 km thick should be resolvable by scattered wave imaging.
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Affiliation(s)
| | - Nick Harmon
- Ocean and Earth ScienceUniversity of SouthamptonSouthamptonUK
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Bureau H, Remusat L, Esteve I, Pinti DL, Cartigny P. The growth of lithospheric diamonds. SCIENCE ADVANCES 2018; 4:eaat1602. [PMID: 29881779 PMCID: PMC5990302 DOI: 10.1126/sciadv.aat1602] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/30/2018] [Accepted: 04/25/2018] [Indexed: 06/08/2023]
Abstract
Natural diamonds contain mineral and fluid inclusions that record diamond growth conditions. Replicating the growth of inclusion-bearing diamonds in a laboratory is therefore a novel diagnostic tool to constrain the conditions of diamond formation in Earth's lithosphere. By determining the carbon isotopic fractionation during diamond growth in fluids or melts, our laboratory experiments revealed that lithospheric monocrystalline and fibrous and coated diamonds grow similarly from redox reactions at isotopic equilibrium in water and carbonate-rich fluids or melts, and not from native carbon. These new results explain why most of the lithospheric diamonds are characterized by a common carbon isotopic fingerprint, inherited from their common parent fluids and not from the mantle assemblage.
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Affiliation(s)
- Hélène Bureau
- Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Sorbonne Université, UMR CNRS 7590, Muséum National d’Histoire Naturelle, IRD UR 206, 4 Place Jussieu, 75252 Paris Cedex 05, France
| | - Laurent Remusat
- Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Sorbonne Université, UMR CNRS 7590, Muséum National d’Histoire Naturelle, IRD UR 206, 4 Place Jussieu, 75252 Paris Cedex 05, France
| | - Imène Esteve
- Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Sorbonne Université, UMR CNRS 7590, Muséum National d’Histoire Naturelle, IRD UR 206, 4 Place Jussieu, 75252 Paris Cedex 05, France
| | - Daniele L. Pinti
- GEOTOP and Département des sciences de la Terre et de l’atmosphère, Université du Québec à Montréal, CP 8888, Succ. Centre-Ville, Montréal, Québec H3C 3P8, Canada
| | - Pierre Cartigny
- LGIS, Institut de Physique du Globe de Paris, Université D. Diderot, UMR CNRS 7154, Paris, France
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Rychert CA, Harmon N, Tharimena S. Scattered wave imaging of the oceanic plate in Cascadia. SCIENCE ADVANCES 2018; 4:eaao1908. [PMID: 29457132 PMCID: PMC5812736 DOI: 10.1126/sciadv.aao1908] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/23/2017] [Accepted: 01/11/2018] [Indexed: 06/08/2023]
Abstract
Fifty years after plate tectonic theory was developed, the defining mechanism of the plate is still widely debated. The relatively short, simple history of young ocean lithosphere makes it an ideal place to determine the property that defines a plate, yet the remoteness and harshness of the seafloor have made precise imaging challenging. We use S-to-P receiver functions to image discontinuities beneath newly formed lithosphere at the Juan de Fuca and Gorda Ridges. We image a strong negative discontinuity at the base of the plate increasing from 20 to 45 km depth beneath the 0- to 10-million-year-old seafloor and a positive discontinuity at the onset of melting at 90 to 130 km depth. Comparison with geodynamic models and experimental constraints indicates that the observed discontinuities cannot easily be reconciled with subsolidus mechanisms. Instead, partial melt may be required, which would decrease mantle viscosity and define the young oceanic plate.
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Savage B. A seismic shift in continental tectonic plates. Science 2017; 357:549-550. [DOI: 10.1126/science.aao1285] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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