Deformation-induced changes in the metamorphic record along rheologically contrasted boundaries: inferences from Cima di Gagnone (Cima Lunga unit, Central Alps)

Maino, Matteo and Corvò, Stefania and Schenker, Filippo and Perozzo, Michele and Tagliaferri, Alessia and Seno, Silvio and Langone, Antonio (2023) Deformation-induced changes in the metamorphic record along rheologically contrasted boundaries: inferences from Cima di Gagnone (Cima Lunga unit, Central Alps). In: Abstract Volume 21st Swiss Geoscience Meeting 21st Swiss Geoscience Meeting, 17-18.11.2023, Mendrisio.

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Abstract

The Cima Lunga unit shows one of the best-preserved record of the deformation and metamorphic history of the Central Alps. Here, the occurrence of ultrahigh-pressure and/or high-temperature rocks embedded within significantly lower grade metamorphic rocks rises a major challenge for developing a consistent geodynamic model for exhumation of such deepseated rocks. Subduction zones are, in fact, efficient player driving material from the surface down into the Earth’s mantle. However, the mechanisms to exhume part of this material (and particularly the denser oceanic rocks) back to the shallow crust are still highly debated. Scientists generally invoke either mechanical decoupling within a tectonic mélange or variable metamorphic re-equilibration during the retrograde path. These interpretations are based on the common assumption that the mineral assemblages form under lithostatic pressure and near-equilibrium regional geothermal gradients. Hence, the resulting metamorphic histories based on the estimation of the pressure and temperature conditions represent the major tool for tectonic reconstruction as proxies of the burial and exhumation history of the rocks during subduction-exhumation phases. Alternative explanations highlight the role of deformation in promoting the coexistence of multiple local equilibria, which cease to correlate with lithostatic conditions and thus burial depths. In this view, the non-hydrostatic stress and the local temperature deviations are accounted as important components potentially modifying the metamorphic system. In this contribution, we show new structural, petrological and geo- and thermos-chronometric data from the Cima Lunga units. The dataset comprises new field mapping covering the entire nappes extension (several hundred square kilometres) and structural, petrological analyses and monazite-zircon U-Pb dating. Our results show the highly variable pressure-temperaturetime-deformation paths experienced by the compositionally heterogeneous rocks of the Cima Lunga and Adula nappes. We present evidence of contrasting metamorphic records among the rocks of these nappes, providing arguments to discuss pros and cons of the tectonic models proposed to explain these contrasting metamorphic records. New findings argue in favour of an exhumation history where deformation and fluids promote local P-T equilibria.

Item Type:	Article in conference proceedings or Presentation at a conference (Poster)
Subjects:	Physical sciences > Geology Physical sciences > Geology > Earth science Physical sciences > Geology > Earth science > Geoscience
Department/unit:	Dipartimento ambiente costruzioni e design > Istituto scienze della Terra
Depositing User:	Filippo Schenker
Date Deposited:	06 Dec 2023 11:22
Last Modified:	06 Dec 2023 11:41
URI:	http://repository.supsi.ch/id/eprint/14800

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