In the Sesia-Lanzo Zone, Western Alps, the Rocca Canavese Thrust Sheets (RCT) subunit is characterized by a mixture of mantle- and crust-derived lithologies, such as metapelites, metagranitoids, metabasics, and serpentinized mantle slices with sizes ranging from meters to hundreds of meters. Structural and metamorphic history suggests that the RCT rocks experienced a complex evolution. In particular, two different peak conditions were obtained for the metabasics, representing different tectono-metamorphic units (TMUs), namely, D1a under eclogite facies conditions and D1b under lawsonite- blueschist-facies conditions. The two TMUs were coupled during the syn-D2 exhumation stage under epidote-blueschist-facies condi- tions. The different rocks and metamorphic evolutions and the abundance of serpenti- nites in the tectonic mixture suggest a possi- ble subduction-related mélange origin for the RCT. To verify whether a subduction-related mélange can record tectono-metamorphic histories similar to that inferred for the RCT, we compare the pressure-temperature evo- lutions with the results of a 2-D numerical model of ocean-continent subduction with mantle wedge serpentinization. The predic- tions of the numerical model fully reproduce the two peak conditions (D1a and D1b) and the successive exhumation history of the two TMUs within the subduction wedge. The de- gree of mixing estimated from field data is consistent with that predicted by the numeri- cal simulation. Finally, the present-day loca- tion of the RCT, which marks the boundary between the orogenic wedge (Penninic and Austroalpine domains) and the southern hin- terland (Southalpine domain) of the Alpine chain, is reproduced by the model at the end of the exhumation in the subduction wedge. Therefore, the comparison between natu- ral data and the model results confirms the interpretation of the RCT as a subduction- related mélange that occurred during exhu- mation within a serpentinized mantle wedge.
Formation and evolution of a subduction-related mélange: The example of the Rocca Canavese Thrust Sheets (Western Alps) / M. Roda, M. Zucali, A. Regorda, M. Iole Spalla. - In: GEOLOGICAL SOCIETY OF AMERICA BULLETIN. - ISSN 0016-7606. - (2019). [Epub ahead of print]
Titolo: | Formation and evolution of a subduction-related mélange: The example of the Rocca Canavese Thrust Sheets (Western Alps) |
Autori: | ZUCALI, MICHELE (Secondo) REGORDA, ALESSANDRO (Penultimo) SPALLA, MARIA IOLE (Ultimo) |
Settore Scientifico Disciplinare: | Settore GEO/03 - Geologia Strutturale Settore GEO/10 - Geofisica della Terra Solida |
Data di pubblicazione: | 2019 |
Rivista: | |
Tipologia: | Article (author) |
Data ahead of print / Data di stampa: | 17-set-2019 |
Digital Object Identifier (DOI): | http://dx.doi.org/10.1130/B35213.1 |
Appare nelle tipologie: | 01 - Articolo su periodico |
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