Balancing cross sections with kinematic constraints: The Dolomites (northern Italy)

Abstract

Balancing of structural cross sections is often hindered by a limited database or tectonic complications. In such cases, kinematic constraints may help to better constrain the construction of a cross section and its extrapolation to depth. The kinematic implications of a known structure (generally at the surface) have to be considered for the unknown structure and for the internal consistency of a cross section. A key point is the quantification of shortening of the known structure. The extrapolation of this parameter allows balancing in an approximate way, emphasizing major structures while minor structures are either neglected or treated in a simplified way. With this approach a quick overview can be achieved on how much leeway for interpretation exists, critical points for testing various working hypotheses become more evident, and the trial‐and‐error effort during the construction of a balanced section is considerably shortened. Still the implications the observed structures have on the deeper crustal levels can be assessed. This concept is applied to a section across the Italian Dolomites, a brittle fold‐and‐thrust belt lacking reflection seismic data so far and thus with a poorly known deep structure. Still active south vergent Alpine thrusting is oriented approximately perpendicular to previous Dinaric thrusting. The ramp flat style is dominant due to rheological constrasts within the stratigraphic sequence. Thanks to kinematic balancing based on surface data, three Alpine thrust systems could be identified, each defining a thrust sheet with its particular basement unit and its sedimentary part. Superposition of the two more external basement units led to the presently observed high elevation of the Triassic sequence in the Dolomites. Shortening since late Miocene times amounts to more than 50 km. Retrodeformation of Alpine thrusting is a key for better understanding the previous Dinaric structures and kinematics.