Abstract
We present a detailed description of the tectono-stratigraphic architecture of the eclogite-facies Internal Piedmont Zone (IPZ) metaophiolite, exposed in the Lanzo Valleys (Western Alps), which represents the remnant of the Jurassic Alpine Tethys. Seafloor spreading and mantle exhumation processes related to the Alpine Tethys evolution strongly conditioned the intra-oceanic depositional setting, which resulted in an articulated physiography and a heterogeneous stratigraphic succession above the exhumed serpentinized mantle. “Complete” and “reduced” successions were recognized, reflecting deposition in morphological or structural lows and highs, respectively. The “complete” succession consists of quartzite, followed by marble and calcschist. The “reduced” succession differs for the unconformable contact of the calcschist directly above mantle rocks, lacking quartzite and gray marble. The serpentinite at the base of this succession is intruded by metagabbro and characterized at its top by ophicalcite horizons. Mafic metabreccia grading to metasandstone mark the transition between the “complete” and “reduced” successions. The character of the reconstructed succession and basin floor physiography of the IPZ metaophiolite is well comparable with the Middle Jurassic–Late Cretaceous succession of both the Queyras Complex (External Piedmont Zone) and the Internal Ligurian Units (Northern Apennines) and with modern slow-spreading mid-ocean ridges.
Highlights
During the rifting stage and seafloor spreading evolution of oceanic basins, the ocean floor commonly results the object of a strong tectono-stratigraphic mobility in response to the development of different types of active tectonic structures at different scales, such as extensional detachment faults, fracture zones, and transfer and tear faults
We present a detailed description of the tectono-stratigraphic architecture of the eclogitefacies Internal Piedmont Zone (IPZ) metaophiolite, exposed in the Lanzo Valleys (Western Alps), which represents the remnant of the Jurassic Alpine Tethys
Sectors to the east and SE of the Nero Lake and to the west of the Malciaussia Lake are characterized by a “complete” stratigraphic succession (Figures 2a and 7) which is defined by the occurrence of all the terms of the lithostratigraphic succession above the mantle rocks
Summary
During the rifting stage and seafloor spreading evolution of oceanic basins, the ocean floor commonly results the object of a strong tectono-stratigraphic mobility in response to the development of different types of active tectonic structures at different scales, such as extensional detachment faults, fracture zones, and transfer and tear faults (see, e.g., in [1,2,3,4,5,6,7]). The exposure of mantle rocks on the seafloor is associated with serpentinization and ophicarbonation processes [7,19,20,21], which may form primary weakness horizons within the oceanic mantle During convergence tectonics both the intra-oceanic tectonic structures (i.e., extensional detachment faults, fracture zones, and transfer and tear faults) and the heterogeneous stratigraphy with its internal rheological contrasts (see, e.g., in [5,7,8,9,10,11,12,13,14,15,16] and references therein), represent, among others, important inherited weakness zones along which tectonic deformation commonly localizes (see, e.g., in [17,18,21,22,23,24,25,26,27,28,29,30]). In exhumed polyphasic and metamorphosed orogenic belts, such as the Western Alps, the reconstruction of the pre-orogenic physiography of the oceanic basin (i.e., the Jurassic Alpine Tethys) is strongly complicated by the overprinting of a multistage, intense deformation and metamorphic recrystallization that these belts experienced during a complete orogenic cycle of oceanic subduction, continental collision, and exhumation
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