The Constraints to the Subsidence and Exhumation of Alpine Units and the Tertiary Piedmont Basin, NW Italy

Abstract

The vertical movements of the orogenic Ligurian Alps and their overlying Tertiary Piedmont Basin (NW Italy) are defined in this work by low-temperature thermochronometers, i.e. apatite (U-Th)/He and fission track. Thermochronological analyses are integrated by seismic and field geological data. Since earliest Oligocene, metamorphic Alpine rocks were exposed, eroded and covered by continental to marginal-marine deposits of the Tertiary Piedmont Basin. Then, the orogenic rocks and the sedimentary succession suffered a km-scale subsidence on the order of 4km before 26 Ma and began their exhumation thereafter: inversion took place in the southernmost part of the Tertiary Piedmont Basin and a regional northwards syn-depositional tilting began. Since Late Oligocene, the evolution of the investigated area is characterized by the coexistence of exhumation/uplift to the south and subsidence to the north. This couple of exhumation and subsidence migrated northwards through time.