Investigators:	Hans G. Avé Lallemant
Collaborators:	Reinoud L.M. Vissers, Utrecht University, The Netherlands Martyn R. Drury, Utrecht University, The Netherlands
Funding Source:	Nederlandse Organisatie voor Wetenschappelijk Onderzoek

Lherzolite (= two-pyroxene peridotite) complex (reddish rocks) at the Etang de Lers (old spelling Lherz), southwestern France

Abstract

From the mid-Cretaceous to the Eocene the North Pyrenean Fault Zone (NPFZ) in southwestern France was an active trans-extensional structure. This extension was very strongly left-oblique. Lherzolite (two-pyroxene, chromian spinel peridotite) bodies, a few meters to several kilometers long, were emplaced from the upper mantle into the NPFZ. The processes of exhumation are believed to be related to extension during rifting along the NPFZ, a mysterious fluidization processes, and thrusting during Eocene to Miocene left-oblique trans-contraction. The project involves detailed study of the lithology, structures, fabrics (textures), and geochemistry of these upper mantle rocks and their relationship to magmatic rocks that occur in the NPFZ as well. This study will constrain the mechanism of rifting, i.e., was the rifting active, passive, or possibly hybrid? What was the role of mantle shear zones? What was the thermal history of the mantle underneath the developing rift? What ductile flow mechanisms resulted in the seismic anisotropy in the upper mantle?