Virtual outcrop modelling and petrography of a heterogeneous gabbroic outcrop in the Ivrea-Verbano Zone, Italy

Investigating magmatic processes in exhumed lower continental crust is often complicated by metamorphic and tectonic overprints postdating magma emplacement. To decrypt these requires integrated structural and petrological analyses at multiple scales. This study provides a new Virtual Outcrop Model (VOM) combined with structural and petrographic analyses of a ∼83 m long outcrop within the Mafic Complex of the Ivrea-Verbano Zone (IVZ), Italy, representing an exhumed section of the lower continental crust. The outcrop is mainly composed of hornblende gabbronorites with variabilities in garnet textures and modal abundances. The main foliation shows local changes in orientation but is generally sub-parallel to the Insubric line. We identify previously unreported olivine-hornblende garnetite and garnet hornblendite lenses, often associated with anorthosite lenses by gradual contacts. Garnet-olivine gabbro occurs in the northern and southern zones of the outcrop. A metamorphic overprint is indicated by: (i) granoblastic to polygonal textures with triple junctions, (ii) rutile exsolution in orthopyroxenes, (iii) hercynite exsolution in plagioclase and (iv) coronitic garnet formed around oxides and olivine. Previously unreported mafic pegmatites crosscut by pseudotachylytes were also identified. Alpine-related faults and shear structures crosscut all lithologies, but detailed field observations combined with analyses of the VOM facilitated the conclusion that the original, pre-alpine spatial relationships between the different magmatic units have not been significantly altered. The lithological sequence and mineralogical variability of this outcrop can, therefore, be used for future detailed studies to assess the primary magmatic processes and subsequent metamorphic pressure-temperature path that affected this portion of the lower continental crust.