Underthrusting and exhumation of continent-derived units within orogenic wedge: an example from the Northern Apennines (Italy)

Abstract

The Punta Bianca Unit (NW Italy) is a continent-derived metamorphic unit that experienced underthrusting and later exhumation in the hinterland sector of the Northern Apennines fold-and-thrust belt. We present a novel 1:5000 scale geological map that aims to illustrate the polyphase tectonic evolution of the Punta Bianca Unit and its relationships with non-metamorphic units. The geologic data presented in the map are coupled with the structural analysis of the main tectonic elements, lithostratigraphic, finite strain and microstructural data that allow to highlight the tectonic history of the study area. In particular, we recognized that the Punta Bianca Unit underwent an early phase of underplating (D1), followed by syn-orogenic exhumation to shallow crustal levels and coupling with the overlying Tuscan Nappe (D2), and nappe stacking/refolding (D3). Low-angle semibrittle (D4) and high-angle brittle (D5) faulting affected both the Punta Bianca Unit and the Tuscan Nappe during the latest stages of deformation.

Keywords

• northern apennines
• exhumation
• fold-and-thrust belt
• polyphase deformation
• orogenic wedge
• greenschist-facies