HR: 1330h
AN: T43B-02    [Abstracts]
TI: Is the Subduction Actually a Mantle Wedge Upduction? Clues and Interpretations From the Mediterranean Arcs
AU: * SCALERA, G
EM: scalera@ingv.it
AF: INGV-Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, Roma, I-00143 Italy
AB: Recent reviews of large scale seismic tomographies show that the prolongation of the rigid/colder lithospheric slab up to the core mantle boundary is not clearly recognizable. Often the tomographic image of these high-velocity bodies become horizontal - at the deep of the 640 km discontinuity - and often it continues to bend coming back toward the upper mantle. Because the strict similarity of some Italian and Mediterranean tectonic situations to the East Asia tectonics - arcs, trenches, Wadati-Benioff zones, volcanic and seismic activities, and the above mentioned horizontal bending of the alleged lithospheric slab -, many clues are examined in search of new interpretations of the Mediterranean geological and observational evidence, with the aim to find solutions that are exportable to the problems of the circumpacific arc-trench zones. The inspection of facts coming from surface geology, magmatism, geochemistry, different method tomographies, etc., is at variance with the alleged Africa-Eurasia convergence. The clues for rifting prevail on those for compression, and many tectonic situations previously interpreted as due to plates' collision, are associated or mixed to rifting evidence. The high velocity bodies characterizing the Wadati-Benioff zone connect gently with large extents of anomalous high velocity mantle trapped in the transition zone. Then the proposal is put forward that uprising - or upduction - of mantle material wedges - driven by isostasy - between two separating lithospheric plates could be a new work hypothesis. Because on an expanding Earth the Mediterranean region has ever had a little latitudinal extension, it is possible in this view, to identify as Mediterranean phases of opening also the Paleo Tethys and Neo Tethys currently alleged `closures', which have added to the Proterozoic nuclei the Variscan and Alpine terranes respectively. These phases and their orogens have to be considered as extensional phases, and the added terranes of African provenance (e.g. the Adriatic fragment) should be regarded as fragments left behind by the going away continental Africa. The recent Sumatra large earthquake has provided an important geophysical data in favour of the views expressed in this contribution.
DE: 8109 Continental tectonics--extensional (0905)
DE: 8125 Evolution of the Earth
DE: 8150 Plate boundary--general (3040)
DE: 8180 Tomography
SC: Tectonophysics [T]
MN: 2005 Joint Assembly