Dados da Submissão

Título

POLYMETAMORPHISM IN A FOSSILIZED PASSIVE MARGIN (SOUTHERN ALPS, ITALY): FROM OROGENY TO RIFT.

Texto do resumo

A well-preserved remnant of the middle crust of the former Adriatic passive margin is exposed in the Southern Alps (Italy). The Dervio–Olgiasca Zone is located south of the Insubric Line along the northern part of Como Lake and, because of the lack of Alpine overprint, provides favourable conditions to investigate the pre-Alpine (Variscan and rift-related) history. We reconstruct the P–T–t–d evolution of the Adria middle crust through petrological (petrography, mineral chemistry, thermobarometry and thermodynamic modelling) and geochronological (Lu/Hf in garnet and U–Pb in monazite) data from pegmatites and host micaschists. These data allow reconstruction of a complex tectono-thermal evolution of the future proximal Adriatic margin at the onset of Alpine rifting. The amphibolite-facies Carboniferous orogenic metamorphic basement (7.6–10 kbar, 610–660 °C at 318–312 Ma) was affected by pervasive extensional deformation (5.1–7.6 kbar, 580–660 °C) in the Middle- to Late-Permian (257.5 ± 3.8 Ma). Pegmatite intruded at 249.8 ± 1.1 Ma in an extensional phase that re-equilibrated the basement rocks at 3.5–4.5 kbar, 560–600 °C. During the Middle- to Late-Triassic (241–235 Ma), the basement experienced static thermal recrystallization (T = 689 ± 41 °C, 5.0 kbar). This study reveals that the local post-Carboniferous thinning and heating events recorded in the Adriatic middle crust were interconnected to other processes occurring at different crustal levels, driven by crustal stretching during the early stages of Alpine rifting.

Palavras Chave

Tectonothermal evolution; P-T-t-d path; Polymetamorphism; extensional dynamics; Passive margin.