Metamorphic evolution of the Sesia-Lanzo Zone, Western Alps: time constraints from multi-system geochronology

Article Abstract:

Multi-system isotopic surveys of the Sesia-Lanzo Zone reveal different stages of the P-T-deformation evolution that are consistent with the established geotectonic Alpine orogeny framework. The Rb-Sr white mica and U-Pb sphene data restrict the age of eclogite facies metamorphism/deformation to 60-70 Ma and suggest that EMC recrystallization is behind sphene growth. The behavior is unlike similar lithologies in the Gneiss Minuti Complex and the isotopic data is unable to distinguish between two mechanical contiguity models. The results indicate at least three tectonic Alpine collision slices.

Isotopes, Geology, Structural, Structural geology

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Trace element modelling of pelite-derived granites

Article Abstract:

Vapour phase occurrence in the incongruent melting of muscovite and biotite identified quantitative trace-element models of metapelites with the consideration of the restite-melt equilibrium. The distribution of rubidium (Rb), strontium (Sr) and barium (Ba) could serve as a basis in determining the presence or absence of a vapour phase during melting. Muscovite incongruent melting with a vapour phase resulted in low Rb/Sr and high Sr/Ba ratios while absence of a vapour phase gave high Rb/Sr and low Sr/Ba ratios. Biotite meltings featured higher concentrations of Rb than muscovite meltings.

Trace analysis, Biotite

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Dating deformation using Rb-Sr in white mica: greenschist facies deformation ages from the Entrelor shear zone, Italian Alps

Article Abstract:

The use of Rb-Sr analysis of white mica facilitates the determination of the age of deformation of high-strain greenschist facies rocks from the Entrelor shear zone system of the western Alps. The technique provides indistinguishable white mica Rb-Sr ages along 30 km of the same shear zone. The dating method shows that if crystallization or dynamic recrystallization occurs below the closure temperature and allows exchange of Sr in white mica with the Sr reservoir, the age yielded by the micas is the age of deformation. It can be used to test kinematic models in orogens.

Research, Usage, Natural history, Rock deformation, Italian Alps, Isotope geology

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