Leucocratic Dykes in Bocchetta di Campo

Geochemical and geochronological investigation of leucocratic dykes in Bocchetta di Campo (northern Ivrea-Verbano Zone)

Student : Claudio Schulthess

Supervisor: Prof. Dr. Max W. Schmidt, Dr. Andrea Galli (m)

During the mapping investigation in the area of Bocchetta di Campo (northern Ivrea-Verbano-Zone) several leucocratic dykes, wherlitisation of the mantle peridotite, alkaligabbros and carbonatites were found (Gobbi, in prep.). In this study the leucocratic dykes were characterised in major and trace elements, and dated, as they were thought to be involved in the formation of the carbonatites (e.g. Widendorfer et al., 2016) and the metasomatic alteration.
The macroscopic and microscopic description of the rocks indicates that most of the samples are syenites while one is a nepheline syenite according to the Streckeisen (QAPF)-diagram.
For the dykes, a Triassic and concordant emplacement age of 223.8+-3.4 Ma was determined. Similar ages were established for the carbonatites at Bocchetta di Campo (Gobbi, in prep.) and for syenites near Finero (Stähle et al., 1990), indicating a possible connection between the three rocks. For the former this connection is also shown in the trace element composition.
According to the trace element analysis the dykes can be divied into two groups. The first shows similarities to the carbonatites and alkaligabbros, whereas for the second one no reference rocks were found.