A tectonic mixing of thin slivers of calcschist, fine-grained gneisses (metasediments and metagranitoids), quartzite, metabasites and serpentinites occurs all along the western margin of central and southern Sesia-Lanzo Zone (SLZ - Austroalpine Domain) at the boundary with Piemonte Zone (PZ) metaophiolites, and extends from Santanel klippe to Lanzo Massif, over a distance of 50 km. All the rocks belonging to SLZ and PZ together underwent four episodes of deformation, giving rise to a complex regional tectonostratigraphy. The metamorphic mineral assemblages marking successive foliations, detected from the central to the southern part of the SLZ western margin, indicate that various metamorphic conditions dominate in different portions of this tectonic mixing. In the southern sector of this “mixing zone” parageneses marking superposed foliations indicate that rocks of SLZ and PZ experienced an early eclogite facies imprint, followed by reequilibration under blueschist facies conditions, and that they were finally widely retrogressed under greenschist facies conditions, during the last two deformational stages. The strong syn-metamorphic deformation of this rock assemblage leaves, at the moment, the interpretation on its origin open: i) the present day configuration could be entirely due to transposition that occurred in a mantle wedge at the early stages of deformation, up to eclogite facies conditions, during active subduction; ii) a detrital origin of these alternating layers of terrigeneous and carbonaceous rocks may correspond to a primary sequence of an extensionally-thinned continental margin reworked in the Alpine subduction system. Similar kinds of “tectonic mélange” of continental and oceanic crustal slices, with variably serpentinized peridotites, are expected to be generated in an hydrated mantle wedge during ablative subduction as it results by 2D numerical simulations of ocean/continent subduction systems.

Tectonic mixing of continental and oceanic crustal slices at the boundary of the southern Sesia-Lanzo Zone: a reinterpretation of tectonic units in the Piemonte Zone

Gusmeo Thomas
Data Curation
;
2018

Abstract

A tectonic mixing of thin slivers of calcschist, fine-grained gneisses (metasediments and metagranitoids), quartzite, metabasites and serpentinites occurs all along the western margin of central and southern Sesia-Lanzo Zone (SLZ - Austroalpine Domain) at the boundary with Piemonte Zone (PZ) metaophiolites, and extends from Santanel klippe to Lanzo Massif, over a distance of 50 km. All the rocks belonging to SLZ and PZ together underwent four episodes of deformation, giving rise to a complex regional tectonostratigraphy. The metamorphic mineral assemblages marking successive foliations, detected from the central to the southern part of the SLZ western margin, indicate that various metamorphic conditions dominate in different portions of this tectonic mixing. In the southern sector of this “mixing zone” parageneses marking superposed foliations indicate that rocks of SLZ and PZ experienced an early eclogite facies imprint, followed by reequilibration under blueschist facies conditions, and that they were finally widely retrogressed under greenschist facies conditions, during the last two deformational stages. The strong syn-metamorphic deformation of this rock assemblage leaves, at the moment, the interpretation on its origin open: i) the present day configuration could be entirely due to transposition that occurred in a mantle wedge at the early stages of deformation, up to eclogite facies conditions, during active subduction; ii) a detrital origin of these alternating layers of terrigeneous and carbonaceous rocks may correspond to a primary sequence of an extensionally-thinned continental margin reworked in the Alpine subduction system. Similar kinds of “tectonic mélange” of continental and oceanic crustal slices, with variably serpentinized peridotites, are expected to be generated in an hydrated mantle wedge during ablative subduction as it results by 2D numerical simulations of ocean/continent subduction systems.
2018
Conference Abstract Volume
1
150
Maria Iole Spalla, Guido Gosso, Gusmeo Thomas, Gisella Rebay, Manuel Roda, Davide Zanoni, Michele Zucali
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11585/680660
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