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| Titel |
Subduction-Driven Recycling of Continental Margin Lithosphere |
| VerfasserIn |
Alan Levander, Maximiliano Bezada, Fenglin Niu, Imma Palomeras, Sally Thurner, Eugene Humphreys, Ramon Carbonell, Josep Gallart, Michael Schmitz, Meghan Miller |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250107181
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| Publikation (Nr.) |
 EGU/EGU2015-6874.pdf |
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| Zusammenfassung |
| Subduction recycling of oceanic lithosphere, a central theme of plate tectonics, is
relatively well understood, whereas recycling continental lithosphere is more difficult to
recognize, and appears far more complicated. Delamination and localized convective
downwelling are two widely recognized processes invoked to explain the removal of
lithospheric mantle under or adjacent to orogenic belts. Here we describe another process
that can lead to the loss of continental lithosphere adjacent to a subduction zone:
Subducting oceanic plates can entrain and recycle lithospheric mantle from an adjacent
continent and disrupt the continental lithosphere far inland from the subduction
zone.
Seismic images from recent dense broadband seismograph arrays in northeastern South
America (SA) and in the western Mediterranean show higher than expected volumes of
positive anomalies identified as the subducted Atlantic slab under northeastern SA, and the
Alboran slab beneath the Gibraltar arc region (GA). The positive anomalies lie under and are
aligned with the continental margins at depths greater than 200 km. Closer to the surface we
find that the continental margin lithospheric mantle is significantly thinner than expected
beneath the orogens adjacent to the subduction zones. The thinner than expected lithosphere
extends inland as far as the edges of nearby cratonic cores. These observations suggest that
subducting oceanic plates viscously entrain and remove continental mantle lithosphere from
beneath adjacent continental margins, modulating the surface tectonics and pre-conditioning
the margins for further deformation. The latter can include delamination of the
entire lithospheric mantle, as around GA, inferred by results from active and passive
seismic experiments. Viscous removal of continental margin lithosphere creates
lithosphere-asthenosphere boundary (LAB) topography which can give rise to secondary
downwellings under the continental interior far inland from the subduction zone: We image
one under SA and we infer that one or more have occurred in the past under the western
Mediterranean. The process of subduction-driven continental margin lithosphere removal
reconciles numerous, sometimes mutually exclusive, geodynamic models proposed to
explain the complex oceanic-continental tectonics of these two subduction zones. |
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