Deformation partitioning within a sinistral transpression zone along the southwestern margin of the Tauern Window (eastern Alps)

Abstract

AbstractThis study is concerned with a newly recognized structure at the southwestern border of the Tauern Window and the neighbouring Austroalpine basement rocks, the Lappach Structure. Structural and isotopic investigations show that this structure is the result of sinistral transpression and backthrusting along the Austroalpine–Penninic contact. Deformation partitioning and differential exhumation of crustal wedges is documented by a succession of ductile and brittle deformation stages. Two stages are distinguished: (1) up-doming of Penninic units and associated advective heat transfer caused a strong temperature variation with the highest temperatures in central portions of the Tauern Window. Coeval transpression with distributed sinistral shear formed high-temperature, partly annealed fabrics in central portions and lower-temperature fabrics with strong crystallographic preferred orientation of quartz along the Tauern Window margin. Southward decrease of temperatures was matched by increases in stress and deformation intensity. (2) Progressive cooling was accompanied by shear localization, deformation partitioning and fluid infiltration. Overall sinistral shear resolved in a discrete strike slip–fault and south vergent folds with associated thrusts defining a backthrust zone along the southern Tauern margin. Southwards extrusion disturbed previously established palaeo-isogrades and juxtaposed rocks from greater depths against lower-grade metamorphic units. Fluids penetrated faults, reduced shear strength and contributed to shear localization.