Quantifying Early Miocene in-sequence and out-of-sequence thrusting at the Alpine-Carpathian junction

Abstract

A detailed reconstruction of late Oligocene and Early Miocene thrusting at the leading edge of the East Alpine fold-thrust belt is achieved from well data, seismic, and interpretative cross sections. Data are used for constraining the paleogeographic positions of the Alpine thrusts, quantifying in-sequence/out-of-sequence thrust distances, assessing the timing of thrust propagation from structurally higher units into more external ones, and estimating thrust velocities. Results are depicted in five palinspastic maps for time slices between ~26 Ma and ~16 Ma. The termination of foreland-propagating thrusting at the Alpine front is apparently controlled by the subcrop topography of the European basement, which includes a major recess in the east leading to a diachronic along-strike termination of foreland-propagating thrusting with younger thrust ages and higher in-sequence thrust distances in the east. Early locking of foreland-propagating thrusting in the west causes prominent out-of-sequence thrusts which add to the in-sequence thrust distances there. Continuing consecutive detachment of foreland units in the east occurs at rather fast propagation velocities with time intervals between foreland-thrust-propagations ranging between 0.1 and 0.7 Ma. The resulting increase of in-sequence thrust distances from west to east is balanced by out-of-sequence thrusts in the west. The total amount of late Oligocene to Early Miocene thrusting is quantified with a minimum of 51 km. Average thrust velocities range between 4.6 and 5.2 mm/yr. This rate refers to the movement of the basal thrust at the leading edge of the fold-thrust belt, which occurs contemporaneous with the eastward lateral extrusion of the Eastern Alps in the hinterland.