Garnet multi-component diffusion modelling reveals local heat sources affecting the cooling history of the Lepontine dome

Tagliaferri, Alessia and Moulas, Evangelos and Schmalholz, Stefan and Schenker, Filippo (2023) Garnet multi-component diffusion modelling reveals local heat sources affecting the cooling history of the Lepontine dome. In: Abstract Volume 21st Swiss Geoscience Meeting 21st Swiss Geoscience Meeting, 17-18.11.2023, Mendrisio.

Text SGM_2023_Abstract_Volume_s.pdf Download (13MB)

Abstract

The Lepontine dome (Central European Alps) is a metamorphic and structural dome formed by crystalline basement nappes accreted during the Alpine continental collision in the Eocene-Oligocene. The dome is characterized by a widespread Barrovian metamorphism. The peak amphibolite-facies conditions coincide with the final phase of nappe emplacement at ca. 31 Ma, dated via U-Pb zircon dating of syn-tectonic migmatites along the principal shear zone at the base of the Maggia-Adula nappe. The duration of the cooling following the temperature peak is still not well contrained. Therefore, in this contribution we evaluate the apparent cooling rates of paragneisses within the Lepontine dome through inverse diffusion modelling in garnet. Our working procedure consists of: (i) analysis of garnet-rims compositional re-adjustment and (ii) comparison of the obtained cooling rates with 1-dimensional thermal models. We examined six garnet-paragneisses collected at different structural levels within the Lepontine nappe stack. The selected garnet crystals show at their rim a coupled Mg-decrease and Mn-increase, indicative of post-peak temperature retrograde modification. We applied geothermobarometry to determine the post-peak reequilibration conditions and we obtained a cooling rate distribution which varies spatially within the study area. The highest cooling rates are within the Maggia-Adula shear zone, whereas at the base of the footwall nappe the cooling rates are very low. In the migmatitic Southern Steep Belt which borders the Lepontine dome to the south, apparent cooling rates have intermediate values. These results compared with thermal models permit to identify regional patterns related to geodynamic processes. The high cooling rates obtained within the main thrust cannot be explained by regional exhumation processes, but a transient local heat source has to be invoked. An additional spatially-confined heat source can be represented by hot fluids percolation or shear heating.

Item Type:	Article in conference proceedings or Presentation at a conference (Poster)
Subjects:	Physical sciences > Geology Physical sciences > Geology > Earth science Physical sciences > Geology > Geochemistry
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/14802

Actions (login required)

View Item