Omphacite textures in eclogites of the Tauern Window: Implications for the exhumation of the Eclogite Zone, Eastern Alps

摘要

We discuss the relationship of omphacite lattice preferred orientation (LPO) patterns in eclogite and kinematic indicators in the matrix surrounding the eclogite during the very rapid exhumation of the deeply buried Eclogite Zone in the Tauern Window of the Eastern Alps. LPO patterns are presented from profiles parallel to the eclogite stretching lineation across the Eclogite Zone. The omphacite textures show symmetric patterns across the entire Eclogite Zone; only in few cases slight asymmetries are observed. The patterns are characterized by an alignment of {110} with the foliation and a maximum of (001) close to the lineation and are indicative of deformation by intracrystalline glide on the (010) [001] and (110) [001] slip systems. The patterns have close resemblance to S-type LPO patterns and probably developed during the burial and accretion of the eclogites. We argue that the LPO patterns are not related to deformation associated with the very rapid exhumation of the Eclogite Zone. We conclude that exhumation-related deformation was concentrated in the metasedimentary rocks that surround the eclogites, allowing the eclogites to preserve their burial LPO signature during the exhumation process. Kinematic indicators show top-N thrusting at the base of the Eclogite Zone and sinistral strike-slip faulting at the top. Most of the kinematic indicators record blueschist- and greenschist-facies meta-morphic conditions. However, because of the very rapid exhumation of the Eclogite Zone with rates exceeding 36 km Myr~(-1), the kinematic indicators are interpreted to reflect the entire exhumation process from eclogite-facies conditions. We discuss a model according to which the Eclogite Zone was exhumed in an oblique extrusion wedge.