Upper mantle structure in the ocean-continent transition zone: Kamchatka |
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| Authors: | L I Gontovaya S V Popruzhenko I V Nizkous |
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| Institution: | 1.Institute of Volcanology and Seismology, Far East Division,Russian Academy of Sciences,Petropavlovsk-Kamchatskii,Russia;2.OAO LukinCholot,Petropavlovsk-Kamchatskii,Russia;3.Data Service Department,Data and Consulting Section,Schumberger Logelko, Moscow,Russia |
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| Abstract: | We consider results from modeling the crustal and upper mantle velocity structure in Kamchatka by seismic tomography and compare
these with gravity data and present-day tectonics. We found a well-pronounced (in the physical fields) vertical and lateral
variation for the upper mantle and found that it is controlled by fault tectonics. Not only are individual lithosphere blocks
moving along faults, but also parts of the Benioff zone. The East Kamchatka volcanic belt (EKVB) is confined to the asthenospheric
layer (the asthenosphere lens) at a depth of 70–80 km; this lens is 10–20 km thick and seismic velocity in it is lower by
2–4%. The top of the asthenosphere lens has the shape of a dome uplift beneath the Klyuchevskoi group of volcanoes and its
thickness is appreciably greater; overall, the upper mantle in this region is appreciably stratified. A low-velocity heterogeneity
(asthenolith) at least 100 km thick has been identified beneath the Central Kamchatka depression; we have determined its extent
in the upper mantle and how it is related to the EKVB heterogeneities. Gravity data suggest the development of a rift structure
under the Sredinnyi Range volcanic belt. The Benioff zone was found to exhibit velocity inhomogeneity; the anomalous zones
that have been identified within it are related to asthenosphere inhomogeneities in the continental and oceanic blocks of
the mantle. |
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