Kinematic evolution of the Volsci Range: A new overview

The Volsci Range, in the central Apennines of peninsular Italy, object of this contribution, has recently seen a proliferation of hypotheses, often highly controversial, that are mainly concerned with: its kinematic evolution; the nature and the provenance of the Chaotic Complex (Argille Scagliose Auct., hereafter Falvaterra Chaotic Complex) and the time of the tectonic emplacement of this unit; the lack of synorogenic deposits in this range; the age of the onset of both compressional and subsequent estensional deformations. The aim of this work is to further contribute to outline and constrain the geodynamic evolution of the Volsci Range, in the light of new and original field data acquired during original mapping surveys for several projects (CARG Lazio, F° 402 Ceccano at the scale 1:50.000; MURST, Ateneo). The study area comprises the entire Volsci Range s.s., the Middle Latina Valley, the southwestern edge of the Simbruino-Ernici foothhills zone and the eastern Aurunci Mtns. In this area two main tectonic units, characterised by different kinematic histories, have been recognised: the innermost and uppermost Volsci Unit, to the west, and the Simbruino-Ernica Unit; to the east. These two main units are locally separated by an intervening, thin and discontinuous tectonic lense, here indicated as the Falvaterra Chaotic Complex. The Mesozoic sequences of these tectonic units were deposited in a carbonate platform, with considerable lateral differences. In the Lepino sector (NW portion of the Volsci Range) at the top of the Mesozoic sequence scattered outcrops of Lower-Middle Miocene carbonate ramp sediments have been recognised (Carpineto). In the Aurunco-Ausonio sector (southeastern Volsci Range), small relicts of the Falvaterra Chaotic Complex rest tectonically above different terms of the local Cretaceous succession. In the Simbruino-Ernica Unit, after the Paleogene gap, a Middle-Upper Miocene carbonatic ramp succession and synorogenic siliciclastic turbidites (Frosinone Fm.) were deposited. The Falvaterra Chaotic Complex is generally interpreted as a remnant of the Ligurian or Sicilide Complexes. Several Authors believe that its chaotic cover was tectonically emplaced during the Subiligurian Stage (Oligocene-Aquitanian) whilst other Authors refer the emplacement of this unit to Tortonian time. The lithological features of this complex are very different from those typical of the Ligurian or Sicilide Units; it rather displays remarkable analogies with the deposits of a succession that was thrust onto the Frosinone Fm., and that is presently found to the right of the Ausente River (Ausente R. Succession). This succession consists of Upper Cretaceous-Burdigalian p.p. pelagic sediments, Burdigalian p.p.-Lower Tortonian synorogenic sandstones, and Lower Messinian-Lower Pliocene piggy-back deposits. The Falvaterra Chaotic Complex lies above flattened surfaces, at the top of different Cretaceous terrains. These surfaces are coated by ferruginous hard-grounds that exhibit remarkable kinematic features, such as mechanical striae and slickensides. Observations carried out on thin sections of samples collected in these hard-grounds reveal the common occurrence of planctonic foraminifera (late Lower Cretaceous Ticinelle and Hedbergelle or Upper Cretaceous Globotruncana). In this context the occurrence of such hard-grounds suggests the drowning of part of the carbonate platform and its consequent upward evolution toward a pelagic realm: this would have been accommodated by development of a set of southwest-dipping normal faults. The Ausente River Succession was deposited above the hardgrounds; therefore, it belongs to the Volsci Unit and represents a key-feature to constrain different evolutionary stages of this tectonic unit: a) the drow