Titanite petrochronological data across the continental crust section exposed in Val d'Ossola (Ivrea-Verbano Zone, Italy)

Abstract

Titanite-bearing calc-silicates and mafic gneisses, metamorphosed under amphibolite- to granulite-facies conditions, crop out in Val d'Ossola area (Ivrea-Verbano Zone, Italy). The Ivrea-Verbano Zone represents an exhumed section of the pre-Alpine middle to lower continental crust which escaped the Alpine subduction, thus provides a unique opportunity to study continental crustal processes and evolution. Among several samples, three, collected from different locations, were chosen for detailed analyses of titanite. Petrochronology of titanite was performed with Laser ablation split-stream (LASS) technique on petrographic thin sections. Petrochronological results on titanite do not define clear correlations with chemistry except for one sample. Rare earth elements (REE) patterns of titanite from the three samples are apparently different in terms of average concentration (i.e., lower or upper 1000 times CI), shapes and occurrence or absence of Eu negative anomaly. Al/Fe vs ΣLREE and Fe content vs Zr/Y plots show that the studied samples coincide with metamorphic rock field deriving from calc-silicates and mafic protoliths, as previously demonstrated in literature. Any compilations of petrochronological data on titanite from the metamorphic volcano-sedimentary sequence of Val d'Ossola can be found in literature. Therefore, these data represent a new insight on an accessory mineral phase whose significance and scientific interest are rising in the last years. Future studies of the evolution of these kinds of rock, widespread in the high-grade metamorphic basements, will benefit from these data as a term of comparison.

Keywords

• HT metamorphism
• Middle/lower continental crust
• Calc-silicates
• Amphibolites
• Petrochronology
• U–Pb titanite dating