Regional fold structure analysis in the Eastern Alpi Apuane, Northern Apennine

Abstract

The Alpi Apuane represent a large tectonic window within the Northern Apennine in Italy. In this area, not only a complete succession of the tectonic units of the Northern Apennine can be studied, but also the structures that result from at least two Alpine deformational events. The rocks of the Alpi Apuane have been deposited from Triassic to Tertiary times on the Hercynian basement of the passive continental margin of the Apulian plate. The sedimentary succession included meta-dolostones, marbles, metacherts, schists, and turbiditic arenites. During late Oligocene more internal units (the Tuscan Nappe together with the overlying Ligurides and Sub- Ligurides) were thrusted over the External Tuscan Domain (Alpi Apuane). The Alpi Apuane stratigraphic sequence was subject to greenschist facies metamorphosis and severe deformation within a crustal scale shear zone. Kilometrescale tight recumbent folds developed during a first deformation event (D1). The successive crustal shortening resulted in a further tightening of folds and the formation of an antiformal stack geometry with a central culmination. This late phase of D1 produced a curving of N–S (Apenninic) trending folds towards an E–W (anti-Apenninic) trend. During Miocene the overthickened antiform underwent gravitational collapse resulting in the refolding of D1 structures producing D2 open and back folds. The studied field area is located in the Eastern Alpi Apuane between Arni and Isola Santa in an area of anti-Apenninic trending D1 folds. The purpose of this study is to contribute to an understanding of 1. how the anti-Apenninic fold trend is developed in the Eastern Alpi Apuane, 2. how the D2 deformational event influenced the D1 folds in the area, and 3. how the anti-Apenninic fold trend developed.