Titanite petrochronology, phase equilibria modelling and the role of amphibole during decompression: Insights from the Shabogamo Domain, central Grenville Province

Abstract

In this contribution, we present new petrochronological results from samples collected the Shabogamo Domain, of the Grenville Province, Québec, Canada. The Shabogamo domain has a distinct geophysical signature and has been proposed to be linked with the well-studied allochthonous Manicouagan Imbricate Zone. We document a Pressure-Temperature-time (P-T-t) path for an amphibolite sample by combining several approaches including: i) an ordinary least square model able to estimate P-T conditions from amphibole composition using a previously semi-quantitative amphibole thermobarometer ii) titanite petrochronology; iii) phase equilibria modelling; iv) trace element thermometry. We show that single element thermobarometry on titanite and amphibole pairs yield the information necessary to reconstruct a decompression P-T path from peak P-T conditions of 1.8 GPa – 775 °C down to 1.2 GPa – 750 °C and are consistent with results of phase equilibria modelling. Titanite U-Pb geochronology results indicate growth between 987 ± 16 Ma and 969 ± 17 Ma. These results are consistent with U-Pb geochronology on zircon from a dyke that crosscuts the amphibolite and from a deformed leucosome sampled in the domain’s footwall. Zircon from the crosscutting dyke appear to have grown at 985 ± 18 Ma without interaction with garnet, whereas zircon from the deformed leucosomes grew at 972 ± 16 Ma during high-pressure metamorphism. Integrating the results of this study into the regional context outlines the exhumation of a second high-P allochthonous nappe, most likely by ductile extrusion, coeval with the burial of the parautochthonous footwall. This study further supports the growing body of evidence for a major tectonic event during the later phase of the Grenvillian Orogeny.