Evidence from P-to-S mantle converted waves for a flat “660-km” discontinuity beneath Iceland |
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| Affiliation: | 1. School of Earth Sciences and Geological Engineering, Sun Yat-sen University, Guangzhou 510275, China;2. Guangdong Provincial Key Lab of Geological Processes and Mineral Resource Survey, Guangzhou 510275, China;1. CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China;2. Exploration Institute of Anhui Coalfield Geology Bureau, Hefei 230088, China;3. Department of Earth Sciences, University of Torino, Via Valperga Caluso 35, 1-10125 Torino, Italy;4. C.N.R. – I.G.G., Section of Torino, Via Valperga Caluso 35, 1-10125 Torino, Italy;5. Beijing SHRIMP Center, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;1. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;2. Department of Geosciences, The University of Tulsa, Tulsa, OK 74104, USA |
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| Abstract: | Iceland is the type example of a ridge-centered hotspot. It is controversial whether the seismic anomaly beneath it originates in the lower mantle or the upper mantle. Some recent studies reported that the 660-km discontinuity beneath central Iceland is shallow relative to peripheral regions and this was interpreted as an effect of elevated temperature at that depth. We investigate topography of the major upper mantle discontinuities by separating the effects of the topography and volumetric velocity heterogeneity in P receiver functions from 55 seismograph stations. Our analysis demonstrates that a significant (at least 10-km) shallowing of the 660-km discontinuity is only possible in the case of improbably low seismic velocities in the mantle transition zone beneath central Iceland. If, as in previous studies, lateral velocity variations in the mantle transition zone are neglected, the data require a depressed rather than an uplifted 660-km discontinuity. For a reasonable S-wave velocity anomaly in the mantle transition zone (around − 3%) no topography on the 660-km discontinuity is required. This can be explained by the lack of temperature anomaly or an effect of two phase transitions with opposite Clapeyron slopes. |
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