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Chaudhury J, Mitra S. Subcontinental lithospheric mantle discontinuities beneath the Eastern Himalayan Plate Boundary System, NE India. GEOPHYSICAL JOURNAL INTERNATIONAL 2023; 233:2155-2171. [DOI: 10.1093/gji/ggad058] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/19/2023]
Abstract
SUMMARY
We use P-wave receiver function (P-RF) analysis and joint inversion with Rayleigh wave group velocity dispersion data to model the shear wave velocity (Vs) structure of subcontinental lithospheric mantle (SCLM) discontinuities beneath northeast (NE) India. The most prominent SCLM discontinuity is the Hales Discontinuity (H-D) observed beneath the Eastern Himalayan Foreland Basin (Brahmaputra Valley) and Shillong Plateau. The P-to-SV converted phase from the H-D (Phs) is a positive amplitude arrival at ∼10–12 s and has positive moveout with increasing ray-parameter. From joint inversion, the H-D is modelled at a depth range of 90–106 km, with 11–12 per cent Vs increase beneath the Brahmaputra Valley. Beneath the Shillong Plateau the H-D is at a depth range of 86–99 km, with 6–10 per cent Vs increase. An intralithospheric discontinuity (ILD) has been identified in the Shillong Plateau station P-RFs, as a positive amplitude PILDs phase, arriving at 8–8.5 s. This is modelled at a depth range of 66–75 km with Vs increase of 2–9 per cent. We construct 2-D profiles of depth-migrated common-conversion-point stack of P-RFs to distinguish the SCLM discontinuity arrivals from crustal phases. 3-D spline-interpolated surface of the H-D has been constructed to visualize its lateral variations. We use xenolith data from the Dharwar Craton, which has similar geological age, petrology and seismic structure as the Shillong Plateau, to petrologically model the SCLM H-D and ILD Vs structure in NE-India. From the calculated Vs structure we conjecture that the H-D is a petrological boundary between mantle peridotite and kyanite-eclogite, with its origin as metamorphosed paleosubducted oceanic slab, similar to other global observations. We further speculate that the shallower ILD could be formed as a contact between frozen asthenosphere-derived metasomatic melts within the SCLM.
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Affiliation(s)
- Jashodhara Chaudhury
- Department of Earth Sciences, Indian Institute of Science Education and Research Kolkata , Mohanpur 741246 , India
| | - Supriyo Mitra
- Department of Earth Sciences, Indian Institute of Science Education and Research Kolkata , Mohanpur 741246 , India
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Chaudhury J, Mitra S, Sarkar T. Hales Discontinuity in the Southern Indian Continental Lithosphere: Seismological and Petrological Models. JOURNAL OF GEOPHYSICAL RESEARCH: SOLID EARTH 2021; 126. [DOI: 10.1029/2020jb020564] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2020] [Accepted: 12/30/2020] [Indexed: 07/19/2023]
Affiliation(s)
- Jashodhara Chaudhury
- Department of Earth Sciences Indian Institute of Science Education and Research Kolkata Mohanpur West Bengal India
| | - Supriyo Mitra
- Department of Earth Sciences Indian Institute of Science Education and Research Kolkata Mohanpur West Bengal India
| | - Tapabrato Sarkar
- Department of Earth Sciences Indian Institute of Science Education and Research Kolkata Mohanpur West Bengal India
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Wan B, Yang X, Tian X, Yuan H, Kirscher U, Mitchell RN. Seismological evidence for the earliest global subduction network at 2 Ga ago. SCIENCE ADVANCES 2020; 6:eabc5491. [PMID: 32821847 PMCID: PMC7406333 DOI: 10.1126/sciadv.abc5491] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/30/2020] [Accepted: 06/24/2020] [Indexed: 06/11/2023]
Abstract
The earliest evidence for subduction, which could have been localized, does not signify when plate tectonics became a global phenomenon. To test the antiquity of global subduction, we investigated Paleoproterozoic time, for which seismic evidence is available from multiple continents. We used a new high-density seismic array in North China to image the crustal structure that exhibits a dipping Moho bearing close resemblance to that of the modern Himalaya. The relict collisional zone is Paleoproterozoic in age and implies subduction operating at least as early as ~2 billion years (Ga) ago. Seismic evidence of subduction from six continents at this age is interpreted as the oldest evidence of global plate tectonics. The sutures identified can be linked in a plate network that resulted in the assembly of Nuna, likely Earth's first supercontinent. Global subduction by ~2 Ga ago can explain why secular planetary cooling was not appreciable until Proterozoic time.
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Affiliation(s)
- Bo Wan
- State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
| | - Xusong Yang
- State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
| | - Xiaobo Tian
- State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
| | - Huaiyu Yuan
- ARC Center of Excellence from Core to Fluid Systems, Macquarie University, NSW 2109, Australia
- Centre for Exploration Targeting, School of Earth Sciences, The University of Western Australia, WA 6009, Australia
| | - Uwe Kirscher
- Department of Geosciences, Eberhard Karls University Tübingen, Tübingen 72076, Germany
| | - Ross N. Mitchell
- State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
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Gosselin JM, Audet P, Estève C, McLellan M, Mosher SG, Schaeffer AJ. Seismic evidence for megathrust fault-valve behavior during episodic tremor and slip. SCIENCE ADVANCES 2020; 6:eaay5174. [PMID: 32010787 PMCID: PMC6976297 DOI: 10.1126/sciadv.aay5174] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/25/2019] [Accepted: 11/21/2019] [Indexed: 05/31/2023]
Abstract
Fault slip behavior during episodic tremor and slow slip (ETS) events, which occur at the deep extension of subduction zone megathrust faults, is believed to be related to cyclic fluid processes that necessitate fluctuations in pore-fluid pressures. In most subduction zones, a layer of anomalously low seismic wave velocities [low-velocity layer (LVL)] is observed in the vicinity of ETS and suggests high pore-fluid pressures that weaken the megathrust. Using repeated seismic scattering observations in the Cascadia subduction zone, we observe a change in the seismic velocity associated with the LVL after ETS events, which we interpret as a response to fluctuations in pore-fluid pressure. These results provide direct evidence of megathrust fault-valve processes during ETS.
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Affiliation(s)
- Jeremy M. Gosselin
- Department of Earth and Environmental Sciences, University of Ottawa, Canada
| | - Pascal Audet
- Department of Earth and Environmental Sciences, University of Ottawa, Canada
| | - Clément Estève
- Department of Earth and Environmental Sciences, University of Ottawa, Canada
| | - Morgan McLellan
- Department of Earth and Environmental Sciences, University of Ottawa, Canada
| | - Stephen G. Mosher
- Department of Earth and Environmental Sciences, University of Ottawa, Canada
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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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Tharimena S, Rychert C, Harmon N. A unified continental thickness from seismology and diamonds suggests a melt-defined plate. Science 2017; 357:580-583. [PMID: 28798127 DOI: 10.1126/science.aan0741] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2017] [Accepted: 06/21/2017] [Indexed: 11/02/2022]
Affiliation(s)
- Saikiran Tharimena
- Ocean and Earth Science, National Oceanography Centre, University of Southampton, Southampton SO14 3ZH, UK.
| | - Catherine Rychert
- Ocean and Earth Science, National Oceanography Centre, University of Southampton, Southampton SO14 3ZH, UK
| | - Nicholas Harmon
- Ocean and Earth Science, National Oceanography Centre, University of Southampton, Southampton SO14 3ZH, UK
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Rychert CA, Harmon N. Constraints on the anisotropic contributions to velocity discontinuities at ∼60 km depth beneath the Pacific. GEOCHEMISTRY, GEOPHYSICS, GEOSYSTEMS : G(3) 2017; 18:2855-2871. [PMID: 29097907 PMCID: PMC5652234 DOI: 10.1002/2017gc006850] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/03/2017] [Accepted: 06/27/2017] [Indexed: 06/07/2023]
Abstract
Strong, sharp, negative seismic discontinuities, velocity decreases with depth, are observed beneath the Pacific seafloor at ∼60 km depth. It has been suggested that these are caused by an increase in radial anisotropy with depth, which occurs in global surface wave models. Here we test this hypothesis in two ways. We evaluate whether an increase in surface wave radial anisotropy with depth is robust with synthetic resolution tests. We do this by fitting an example surface wave data set near the East Pacific Rise. We also estimate the apparent isotropic seismic velocity discontinuities that could be caused by changes in radial anisotropy in S-to-P and P-to-S receiver functions and SS precursors using synthetic seismograms. We test one model where radial anisotropy is caused by olivine alignment and one model where it is caused by compositional layering. The result of our surface wave inversion suggests strong shallow azimuthal anisotropy beneath 0-10 Ma seafloor, which would also have a radial anisotropy signature. An increase in radial anisotropy with depth at 60 km depth is not well-resolved in surface wave models, and could be artificially observed. Shallow isotropy underlain by strong radial anisotropy could explain moderate apparent velocity drops (<6%) in SS precursor imaging, but not receiver functions. The effect is diminished if strong anisotropy also exists at 0-60 km depth as suggested by surface waves. Overall, an increase in radial anisotropy with depth may not exist at 60 km beneath the oceans and does not explain the scattered wave observations.
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Park J, Levin V, Brandon M, Lees J, Peyton V, Gordeev E, Ozerov A. A Dangling Slab, Amplified Arc Volcanism, Mantle Flow and Seismic Anisotropy in the Kamchatka Plate Corner. PLATE BOUNDARY ZONES 2013. [DOI: 10.1029/gd030p0295] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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11
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Mapping the Distribution of Fluids in the Crust and Lithospheric Mantle Utilizing Geophysical Methods. LECTURE NOTES IN EARTH SYSTEM SCIENCES 2013. [DOI: 10.1007/978-3-642-28394-9_13] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
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Yue H, Chen YJ, Sandvol E, Ni J, Hearn T, Zhou S, Feng Y, Ge Z, Trujillo A, Wang Y, Jin G, Jiang M, Tang Y, Liang X, Wei S, Wang H, Fan W, Liu Z. Lithospheric and upper mantle structure of the northeastern Tibetan Plateau. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2011jb008545] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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13
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Levander A, Humphreys ED, Ekstrom G, Meltzer AS, Shearer PM. Proposed project would give unprecedented look under North America. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/99eo00181] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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14
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Lithospheric layering in the North American craton. Nature 2010; 466:1063-8. [PMID: 20740006 DOI: 10.1038/nature09332] [Citation(s) in RCA: 377] [Impact Index Per Article: 26.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2009] [Accepted: 06/25/2010] [Indexed: 11/09/2022]
Abstract
How cratons-extremely stable continental areas of the Earth's crust-formed and remained largely unchanged for more than 2,500 million years is much debated. Recent studies of seismic-wave receiver function data have detected a structural boundary under continental cratons at depths too shallow to be consistent with the lithosphere-asthenosphere boundary, as inferred from seismic tomography and other geophysical studies. Here we show that changes in the direction of azimuthal anisotropy with depth reveal the presence of two distinct lithospheric layers throughout the stable part of the North American continent. The top layer is thick ( approximately 150 km) under the Archaean core and tapers out on the surrounding Palaeozoic borders. Its thickness variations follow those of a highly depleted layer inferred from thermo-barometric analysis of xenoliths. The lithosphere-asthenosphere boundary is relatively flat (ranging from 180 to 240 km in depth), in agreement with the presence of a thermal conductive root that subsequently formed around the depleted chemical layer. Our findings tie together seismological, geochemical and geodynamical studies of the cratonic lithosphere in North America. They also suggest that the horizon detected in receiver function studies probably corresponds to the sharp mid-lithospheric boundary rather than to the more gradual lithosphere-asthenosphere boundary.
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Audet P, Bostock MG, Boyarko DC, Brudzinski MR, Allen RM. Slab morphology in the Cascadia fore arc and its relation to episodic tremor and slip. ACTA ACUST UNITED AC 2010. [DOI: 10.1029/2008jb006053] [Citation(s) in RCA: 98] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Chen CW, Rondenay S, Evans RL, Snyder DB. Geophysical Detection of Relict Metasomatism from an Archean (~3.5 Ga) Subduction Zone. Science 2009; 326:1089-91. [DOI: 10.1126/science.1178477] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- Chin-Wu Chen
- Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology (MIT), 77 Massachusetts Avenue, Cambridge, MA 02139, USA
| | - Stéphane Rondenay
- Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology (MIT), 77 Massachusetts Avenue, Cambridge, MA 02139, USA
| | - Rob. L. Evans
- Department of Geology and Geophysics, Woods Hole Oceanographic Institution, MS 22, Woods Hole, MA 02543, USA
| | - David B. Snyder
- Geological Survey of Canada, 615 Booth Street, Ottawa, Ontario K1A 0E9, Canada
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Affiliation(s)
- Catherine A. Rychert
- Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, M/C 0225, La Jolla, CA 92093, USA
| | - Peter M. Shearer
- Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, M/C 0225, La Jolla, CA 92093, USA
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Perry HKC, Jaupart C, Mareschal JC, Bienfait G. Crustal heat production in the Superior Province, Canadian Shield, and in North America inferred from heat flow data. ACTA ACUST UNITED AC 2006. [DOI: 10.1029/2005jb003893] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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19
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Cooper C, Lenardic A, Levander A, Moresi L. Creation and preservation of cratonic lithosphere: Seismic constraints and geodynamic models. ARCHEAN GEODYNAMICS AND ENVIRONMENTS 2006. [DOI: 10.1029/164gm07] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
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20
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Rychert CA, Fischer KM, Rondenay S. A sharp lithosphere–asthenosphere boundary imaged beneath eastern North America. Nature 2005; 436:542-5. [PMID: 16049485 DOI: 10.1038/nature03904] [Citation(s) in RCA: 156] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2004] [Accepted: 05/20/2005] [Indexed: 11/09/2022]
Abstract
Plate tectonic theory hinges on the concept of a relatively rigid lithosphere moving over a weaker asthenosphere, yet the nature of the lithosphere-asthenosphere boundary remains poorly understood. The gradient in seismic velocity that occurs at this boundary is central to constraining the physical and chemical properties that create differences in mechanical strength between the two layers. For example, if the lithosphere is simply a thermal boundary layer that is more rigid owing to colder temperatures, mantle flow models indicate that the velocity gradient at its base would occur over tens of kilometres. In contrast, if the asthenosphere is weak owing to volatile enrichment or the presence of partial melt, the lithosphere-asthenosphere boundary could occur over a much smaller depth range. Here we use converted seismic phases in eastern North America to image a very sharp seismic velocity gradient at the base of the lithosphere-a 3-11 per cent drop in shear-wave velocity over a depth range of 11 km or less at 90-110 km depth. Such a strong, sharp boundary cannot be reconciled with a purely thermal gradient, but could be explained by an asthenosphere that contains a few per cent partial melt or that is enriched in volatiles relative to the lithosphere.
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Affiliation(s)
- Catherine A Rychert
- Department of Geological Sciences, Brown University, Box 1846, Providence, Rhode Island 02912, USA.
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Karlstrom KE, Whitmeyer SJ, Dueker K, Williams ML, Bowring SA, Levander AR, Humphreys ED, Keller GR. Synthesis of results from the CD-ROM Experiment: 4-D image of the lithosphere beneath the Rocky Mountains and implications for understanding the evolution of continental lithosphere. ACTA ACUST UNITED AC 2005. [DOI: 10.1029/154gm31] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/24/2023]
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22
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Wang Q. Shear wave properties and Poisson's ratios of ultrahigh-pressure metamorphic rocks from the Dabie-Sulu orogenic belt, China: Implications for crustal composition. ACTA ACUST UNITED AC 2005. [DOI: 10.1029/2004jb003435] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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23
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Park J, Yuan H, Levin V. Subduction zone anisotropy beneath Corvallis, Oregon: A serpentinite skid mark of trench-parallel terrane migration? ACTA ACUST UNITED AC 2004. [DOI: 10.1029/2003jb002718] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Jeffrey Park
- Department of Geology and Geophysics; Yale University; New Haven Connecticut USA
| | - Huaiyu Yuan
- Department of Geology and Geophysics; Yale University; New Haven Connecticut USA
| | - Vadim Levin
- Department of Geology and Geophysics; Yale University; New Haven Connecticut USA
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Saul J, Vinnik L. Earth science: Mantle deformation or processing artefact? Nature 2003; 422:136; discussion 136. [PMID: 12634776 DOI: 10.1038/422136a] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Joachim Saul
- GeoForschungsZentrum Potsdam, Telegrafenberg, 14473 Potsdam, Germany.
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Abstract
Elastic anisotropy is present where the speed of a seismic wave depends on its direction. In Earth's mantle, elastic anisotropy is induced by minerals that are preferentially oriented in a directional flow or deformation. Earthquakes generate two seismic wave types: compressional (P) and shear (S) waves, whose coupling in anisotropic rocks leads to scattering, birefringence, and waves with hybrid polarizations. This varied behavior is helping geophysicists explore rock textures within Earth's mantle and crust, map present-day upper-mantle convection, and study the formation of lithospheric plates and the accretion of continents in Earth history.
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Affiliation(s)
- Jeffrey Park
- Department of Geology and Geophysics, Yale University, Post Office Box 208109, New Haven, CT 06520-8109, USA
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27
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Rondenay S, Bostock MG, Shragge J. Multiparameter two-dimensional inversion of scattered teleseismic body waves 3. Application to the Cascadia 1993 data set. ACTA ACUST UNITED AC 2001. [DOI: 10.1029/2000jb000039] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Shragge J, Bostock MG, Rondenay S. Multiparameter two-dimensional inversion of scattered teleseismic body waves 2. Numerical examples. ACTA ACUST UNITED AC 2001. [DOI: 10.1029/2001jb000326] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Schulte-Pelkum V, Masters G, Shearer PM. Upper mantle anisotropy from long-periodPpolarization. ACTA ACUST UNITED AC 2001. [DOI: 10.1029/2001jb000346] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Abstract
Since Mohorovicić discovered a dramatic increase in compressional seismic velocity at a depth of 54 km beneath the Kulpa Valley in Croatia, the 'Moho' has become arguably the most important seismological horizon in Earth owing to its role in defining the crust-mantle boundary. It is now known to be a ubiquitous feature of the Earth, being found beneath both the continents and the oceans, and is commonly assumed to separate lower-crustal mafic rocks from upper-mantle ultramafic rocks. Electromagnetic experiments conducted to date, however, have failed to detect a corresponding change in electrical conductivity at the base of the crust, although one might be expected on the basis of laboratory measurements. Here we report electromagnetic data from the Slave craton, northern Canada, which show a step-change in conductivity at Moho depths. Such resolution is possible because the Slave craton is highly anomalous, exhibiting a total crustal conductance of less than 1 Siemens--more than an order of magnitude smaller than other Archaean cratons. We also found that the conductivity of the uppermost continental mantle directly beneath the Moho is two orders of magnitude more conducting than laboratory studies on olivine would suggest, inferring that there must be a connected conducting phase.
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Affiliation(s)
- A G Jones
- Geological Survey of Canada, Ottawa, Ontario.
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Rondenay S, Bostock MG, Hearn TM, White DJ, Ellis RM. Lithospheric assembly and modification of the SE Canadian Shield: Abitibi-Grenville teleseismic experiment. ACTA ACUST UNITED AC 2000. [DOI: 10.1029/2000jb900022] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Affiliation(s)
- Karen M. Fischers
- K. M. Fischer is in the Department of Geological Sciences, Brown University, Providence, RI 02912, USA
| | - Rob D. van der Hilst
- R. D. van der Hilst is in the Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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