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Abstract: The "Arc De Castellane" (Southern French Alps): A Transfer/Thrust Arc Induced by Southward Alpine Extrusion and Controlled by Inherited Mesozoic Normal Fault Pattern

Jean-Francois Stephan, Corinne Pelline, Michael Popoff, Olivier Laurent, Charles Aubourg

The "Arc de Castellane" together with the "Arc de Nice" belong to the southern French Alps. They are both related to the Miocene southward extrusion of the internal Western Alps along major South to SSW directed dextral strike- slip faults. These arcs are mostly thin skin belts generated above the upper Triassic evaporites, at the southern edge of the Mercantour-Barrot back-stop.

The "Arc de Castellane" has a L shape, with a western front trending N-S and a southern one striking E-W. Strain and kinematic indicators show that the former (which includes the famous Digne Nappe) can be regarded as a mega dextral oblique ramp whereas the latter is almost perpendicular to the main shortening and transport direction. Paleomagnetic data indicate that no major rotation has occurred during and after the arc genesis.

Tectonic and sedimentary detailed studies show that the L shape and the internal tectonic pattern of the arc have been strongly influenced by Jurassic to Cretaceous normal faults striking N-S, E-W, NE-SW and NW-SE. The L shape corresponds indeed to the former boundary between the southern Provence platform and the northern Dauphinois marginal basin. Most of the normal faults in the sedimentary cover have been reactivated as strike-slip faults, oblique ramps or reverse faults depending on their original strike. Normal faults in the basement have tightly controlled the geometry of the folds and thrusts on both sides of the arc.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France