Zircon Investigation

Zircon investigation in a carbonate dike of Val Mastallone, Ivrea-Verbano Zone (northern Italy)

Student : Gino Sartori

Supervisors Prof. Dr. Max W. Schmidt; Dr. Andrea Galli, Institute of Geochemistry and Petrology

The Ivrea Verbano Zone represents one of the best studied case of magmatic underplating in the world. Carbonate rocks occur widespread through the entire Ivrea-Verbano Zone, both as concordant marble bodies or as discordant carbonate dike. Some of those dikes present characteristics that indicate a probable intrusion of carbonatitic magma into the crust. One of those carbonate dike was found in Val Mastallone, together with Val Grande and Val Sermenza one of the three main valley of Valsesia.

Because of the particular and favorable geological setting of the region, the fascinating prospective of confirming the first carbonatite dikes of the Alps could be taken in account.

Outcrops features such as clinopyroxenite xenoliths different from the host rocks indicate that this dike effectively experienced a magmatic stage. Geochemical analysis on zircons extracted from the carbonate matrix allows to separate them into two morphological and geochemical groups. The one counts twenty-four faint-zoned 186 Ma old zircons, the other five 300 Ma old zoned zircons. The Jurassic age of the youngest group, unique for the region, as well as its geochemical and morphological features, confirm an intrusion of carbonatitic magma into the mafic-complex. This intrusion is probably related to the early stage of opening of the Thetyan see. On the other hand, the trace elements content of the older group suggests a probable inheritance from the host rock.