Deformation- dependent P-T variations within a compositionally heterogeneous shear zone: integration of structural and petrological investigations, U-Th-Pb dating and numerical modelling from Cima di Gagnone (Cima Lunga Unit, Central Alps)

Maino, Matteo and Corvò, Stefania and Casini, Leonardo and Langone, Antonio and Schenker, Filippo and Seno, Silvio (2019) Deformation- dependent P-T variations within a compositionally heterogeneous shear zone: integration of structural and petrological investigations, U-Th-Pb dating and numerical modelling from Cima di Gagnone (Cima Lunga Unit, Central Alps). In: Abstract Volume. Emile Argand Conference on Alpine Geological Studies 2019 Emile Argand Conference on Alpine Geological Studies 2019, Sion.

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Abstract

The Cima Lunga Unit in the Central Alps consists of continental basement rocks (orthogneisses, paragneisses and metapelites) enclosing small inclusions of oceanic crust (eclogites, amphibolites and peridotites). All lithotypes are pervasively folded and sheared during the Alpine orogenic phases, resulting in a high-strained nappe with estimated shear strain γ>10. Since their discovery, the ultra-basic rocks received the major attention as they preserve ultra-high pressure eclogite-facies assemblages with peak metamorphic conditions up to 2.5 GPa and 750 °C in the Cima di Gagnone area. The metamorphism of the host rock –i.e. the gneiss complex –is instead constrained at considerably lower P-T conditions (up to 0.8 Gpa and 660 °C). These contrasting thermodynamic histories rise a major challenge for developing a consistent geodynamic model. The coexistence, at the outcrop scale, of such different metamorphisms implies either extreme mechanical decoupling or extremely variable metamorphic equilibrium during Alpine subduction. Our research addresses the link between metamorphism and deformation focusing on the positive feedbacks of tectonic stress on the development of apparently incompatible metamorphic patterns. We present coupled structural and petrological investigations (thermo-barometry and thermodynamic modelling) with the aim to characterize the possible composition- and stress-dependent variation in metamorphic conditions, as well as their magnitude with respect to the relative position in the inclusion-matrix network. The resulting pressure-temperature paths are temporally constrained with U-Th-Pb dating of monazite, which is crucial to determine the relative timing between metamorphic and deformation processes. Field and laboratory-data are finally compared with the results obtained from elasto-visco-plastic 2D Finite Difference models.

Item Type:	Article in conference proceedings or Presentation at a conference (Speech)
Subjects:	Physical sciences Physical sciences > Geology
Department/unit:	Dipartimento ambiente costruzioni e design > Istituto scienze della Terra
Depositing User:	Filippo Schenker
Date Deposited:	18 Dec 2019 07:54
Last Modified:	18 Dec 2019 07:54
URI:	http://repository.supsi.ch/id/eprint/11365

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