Using postglacial sea level,crustal velocities and gravity-rate-of-change to constrain the influence of thermal effects on mantle lateral heterogeneities |
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| Institution: | 1. Institute of Geodesy and Geophysics, Chinese Academy of Sciences, Wuhan 430077, China;2. Department of Geoscience, University of Calgary, Alberta, Canada T2N 1N4;3. Department of Geomatics Engineering, University of Calgary, Alberta, Canada T2N 1N4;1. LIENSs, Université de la Rochelle – CNRS, 2 rue Olympe de Gouge, 17000 La Rochelle, France;2. School of Land and Food, University of Tasmania, Hobart, Australia;3. Research Institute for Water and Environment, University of Siegen, Siegen, Germany;4. Mediterranean Institute for Advanced Studies, UIB-CSIC, Esporles, Spain;5. Dipartimento di Scienze Pure e Applicate, Università degli Studi di Urbino Carlo Bo, Urbino, Italy;1. Department of Polar Science, School of Multidisciplinary Sciences, The Graduate University for Advanced Studies (SOKENDAI), Japan;2. National Institute of Polar Research, Tokyo, Japan;3. Faculty of Social Sciences, Hosei University, Tokyo, Japan;1. Physics of Ice, Climate and Earth, Niels Bohr Institute, University of Copenhagen, Tagensvej 16, DK-2200, Copenhagen, Denmark;2. MARUM – Center for Marine Environmental Sciences, University of Bremen, Leobener Strasse 8, 28359, Bremen, Germany;3. Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964-8000, USA;4. Department of Earth and Planetary Sciences, Northwestern University, Evanston, IL 60208, USA;5. School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK;6. College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, USA;7. GEOTOP-UQAM, CP 8888 Montréal, H3C 3P8, Canada;8. Department of Geological Sciences, University of Florida, Gainesville, FL 32611, USA;9. Department of Geoscience, University of Wisconsin, Madison, WI 53706, USA;10. Department of Earth and Planetary Sciences and Institute of Earth, Ocean and Atmospheric Sciences, Rutgers University, New Brunswick, NJ, USA;11. Climate Change Research Centre, PANGEA, The University of New South Wales, Sydney, NSW, Australia;12. Climate and Global Dynamics Laboratory, National Center for Atmospheric Research (NCAR) Boulder, CO 80305, USA;13. Potsdam Institute for Climate Impact Research, Potsdam, Germany;14. Complutense University of Madrid, 28040, Madrid, Spain;15. Geosciences Institute, UCM-CSIC, 28040, Madrid, Spain;p. Department of Earth and Environmental Sciences, Boston College, Chestnut Hill, MA 02467, USA;q. Environmental Change Research Centre, Department of Geography, University College London, England, UK;r. Department of Earth Sciences, University of Cambridge, CB2 3EQ, Cambridge, UK;1. College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, USA;2. Department of Physics and Physical Oceanography, Memorial University, Canada;3. Department of Earth and Planetary Sciences, Harvard University, USA;1. Geography, College of Life and Environmental Sciences, University of Exeter, EX4 4RJ, Exeter, UK;2. Dipartimento di Scienze Della Terra, Università di Pisa, Via S. Maria, 53, 56126, Pisa, Italy;3. Aix-Marseille Université, CNRS-CEREGE, UMR 7330, IRD, Collège de France, INRA Aix en Provence, France;4. Dipartimento Scienze Chimiche e Geologiche, Università Degli Studi di Cagliari, Via Trentino 51, 09127, Cagliari, Italy;5. Università Degli Studi di Urbino, Dipartimento di Scienze Pure e Applicate (DiSPeA), Urbino, Italy;6. Department of Geography, Durham University, South Road, Durham, DH1 3LE, UK;7. CNRS Chrono-Environnement UMR6249, Université de Franche-Comté, UFR ST, Besançon, France;8. University of Bremen, Marum, ZMT, D-28359, Bremen, Germany;9. ICREA, Barcelona, Catalonia, Spain;10. IPHES, Institut Català de Paleoecologia Humana I Evolució Social, Campus Sescelades URV, Tarragona, Catalonia, Spain;11. URV, Àrea de Prehistòria, Universitat Rovira I Virgili, 43002, Tarragona, Catalonia, Spain;12. RIMS, The Leon Recanati Institute for Maritime Studies University of Haifa, Mount Carmel, Haifa 31905, Israel |
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| Abstract: | Lateral heterogeneities in the mantle can be caused by thermal, chemical and non-isotropic pre-stress effects. Here, we investigate the possibility of using observations of the glacial isostatic adjustment (GIA) process to constrain the thermal contribution to lateral variations in mantle viscosity. In particular, global historic relative sea level, GPS in Laurentide and Fennoscandia, altimetry together with tide-gauge data in the Great Lakes area, and GRACE data in Laurentide are used. The lateral viscosity perturbations are inferred from the seismic tomography model S20A by inserting the scaling factor β to determine the contribution of thermal effects versus compositional heterogeneity and non-isotropic pre-stress effects on lateral heterogeneity in mantle viscosity. When β = 1, lateral velocity variations are caused by thermal effects alone. With β < 1, the contribution of thermal effect decreases, so that for β = 0, there is no lateral viscosity variation and the Earth is laterally homogeneous. These lateral viscosity variations are superposed on four different reference models which differ significantly in the lower mantle viscosity. The Coupled Laplace Finite Element method is used to predict the GIA response on a spherical, self-gravitating, compressible, viscoelastic Earth with self-gravitating oceans, induced by the ICE-4G deglaciation model.Results show that the effect of β on uplift rates and gravity rate-of-change is not simple and involves the trade-off between the contribution of lateral viscosity variations in the transition zone and in the lower mantle. Models with small viscosity contrast in the lower mantle cannot explain the observed uplift rates in Laurentide and Fennoscandia. However, the RF3S20 model with a reference viscosity profile simplified from Peltier's VM2 with the value of β around 0.2–0.4 is found to explain most of the global RSL data, the uplift rates in Laurentide and Fennoscandia and the BIFROST horizontal velocity data. In addition, the changes in GIA signals caused by changes in the value of β are large enough to be detected by the data, although uncertainty in other parameters in the GIA models still exists. This may encourage us to further utilize GIA observations to constrain the thermal effect on mantle lateral heterogeneity as geodetic and satellite gravity measurements are improved. |
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