Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007geoji.170.1180t&link_type=abstract
Geophysical Journal International, Volume 170, Issue 19, pp. 1180-1194.
Astronomy and Astrophysics
Astronomy
7
Controlled-Source Seismology, Crust, Fan Profiling, Moho, Western Alps, Wide-Angle Reflection
Scientific paper
The Moho preserves imprints of the regional geodynamic evolution of the lithosphere. As such, its detailed topography in divergence or convergence zones has a strong bearing on any geodynamic model. This is still more critical where 3-D effects are expected, as in the case of the Alpine chain which exhibits in its western part a short radius of curvature while its trend rotates by 180°. The deep structure of this zone, characterized by a peculiar imbrication of high-density material of lower crust or mantle origin, remains a puzzle. In September 1999, a new controlled-source-seismology experiment was carried out in the southwestern Alps, in the area between the Pelvoux, Dora Maira and Argentera massifs. Five shots were recorded with 130 seismic stations deployed on a total of nine fan- and one in-line profiles. It aimed at getting information on the Moho depth in a hitherto blank area, and discussing the existence of the hypothetical Briançonnais mantle flake mapped in 1986 by the ECORS-CROP experiment. Fan profiles recorded at critical distance for reflections from the European Moho allowed us to map in detail the thickening of the crust from the Mediterranean coastline (27km) to the root zone (55km). The zone just south of the Pelvoux massif is characterized by a rather flat, 40-km-deep Moho, which distorts the isobaths in thickening the crust along the Durance valley. Beneath the Argentera massif and just north of it, we evidence a strong dip of the Moho down to 51km, whereas previous maps predicted depths of 40-46km only. A new, detailed map of the European Moho can be drawn, which integrates depth data measured at ~300 reflection midpoints. However, the experiment could not establish the continuity of the Briançonnais mantle flake over a large area in the internal Alps. We observed several reflectors in the 15-31-km depth range. One of them is the Ubaye reflector, a 20-km-long, 23-31-km-deep structure. It might correspond to the Briançonnais mantle flake, although it is located much farther south than the reflector mapped in 1986. New investigations will be necessary to state whether its origin is crustal or due to wedging of mantle material.
Béthoux Nicole
Fréchet Julien
Guiguet R.
Jenatton Liliane
Paul Abhijeet
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