STRUCTURAL ANALYSIS OF THE MESOZOIC LAGONEGRO UNITS IN SW LUCANIA (SOUTHERN ITALIAN APENNINES)

Abstract

This study discusses the structural analysis of the tec­tonic units outcropping in the Lagonegro Zone of SW-Lu­cania (southern Italy). The Mesozoic sediments of the Lagonegro and adjacent nappes have undergone a polyphase deformation history, which is superposed on an already com­plicated Middle Triassic to Lower Cretaceous palaeotecton­ic evolution. Field mapping and structural analysis revealed two main contractional deformation sequences in the Lagonegro nappes. During the early stages of the D1 defor­mation sequence, the Mesozoic sediments of the Lagonegro basin were detached from their substratum. Continued NE­directed thrusting (in present-day co-ordinates) led to nappe formation and to the regional juxtaposition of Lagonegro Unit II over Unit I. Main folding within the two nappes was essentially coeva! with nappe emplacement. Further thrust­ing occurred within Lagonegro Unit I, involving faulting of already folded rocks with only limited displacements com­pared to the main nappe transport. The fold geometry ap­pears to have been often modified by movement over the thrust surfaces: folds tighten and axial planes make progres­sively lower angles with the thrust towards the thrust tip-line. A discontinuously developed slaty cleavage (S1) formed in the less competent lithologies during this deformation se­quence. Refolding of the whole tectonic pile occurred as a consequence of (present-day) N-S to NNE-SSW shortening (D2). In the less competent lithologies, a crenulation cleavage (S2), usually in the form of conjugate kink bands, is as­sociated with this deformation. Refolding produced differ­ent types of interference structures at various scales. The most commonly observed are transitional forms between Type 1 and Type 2 interference patterns. Although these complex structures never represent simple type end-members, at a first approximation a pattern can be recognized consisting of (dominant Type 1) dome-like structures developed on early broad anticlines and of (dominant Type 2) tight synclinal structures with folded axial surfaces developed on early "pinched" synclines.