Petrology and geochronology of the Loro Intrusive Complex (Ivrea-Verbano Zone)

Filippo Formoso, Gianluca Sessa, Enrico Cannaò, Marilena Moroni, Antonio Langone, Massimo Tiepolo

Research output: Contribution to conferenceAbstract


The Loro Intrusive Complex is located in Valle d’Ossola (southern Alps) and is part of the Ivrea-Verbano Zone. Literature data on this igneous complex are relatively scarce (Boriani, 1966) and a detailed geochemical and geochronological study is missing. Therefore, for its location between the northern and the southern Ivrea domains, this
poorly studied igneous complex is important to correctly understand the structure and igneous evolution of the whole Ivrea-Verbano Zone.
The Loro Intrusive Complex crops out along the Canavese Line and is in contact with the “Scisti di Fobello e Rimella” to the west and with mafic and felsic granulites of the Kinzigite formation to the east. Within the whole complex slices of basement rocks including milonitic granulites, marbles and serpentinites are locally found. Diorites
and hornblendites are the main lithologies of the Loro Intrusive Complex. Diorites are relatively fine-grained and consist of pargasitic amphibole (60 vol%) and plagioclase (40 vol%) with average An contents of 47 mol%. A strongly altered clinopyroxene (Mg# = 0.7) is locally found. Hornblendites consists of brown amphibole and accessory
plagioclase. The chondrite normalized Rare Earth Element (REE) pattern of clinopyroxene is characterized by a marked light–(L)REE enrichment (22 times CI chondrite) relative to heavy (H)-REE, which are at about 5 times CI chondrite (GdN/YbN up to 3.8). The REE pattern of amphibole is enriched in LREE (40 times CI chondrite) and HREE are about 15 times CI chondrite (GdN/YbN = 1.5). Occasionally a positive Eu anomaly characterizes the REE pattern of amphibole.
U-Pb geochronology was carried out with laser ablation ICP-MS on zircons from diorites. Zircon grains have round shape, thus suggesting a xenocrystic origin. Under cathodoluminescence they are generally homogeneous and rarely show ghost zoning. Most of zircons gave discordant U-Pb dates, only few grains are concordant and allowed to calculate a concordant date at 278±3 Ma (2s). This date is interpreted as the age of reset of the U-Pb system induced by the intrusion of the dioritic rocks.
Similarities between the Loro and the Finero intrusive complexes were already suggested by Boriani (1966). These new results demonstrate a close geochemical affinity between the two complexes; in particular, peculiar similarities in
terms of trace element composition of minerals are observed (e.g., the positive Eu anomaly in amphibole). The inferred age of intrusion suggests that the Loro intrusive complex belongs to the same mantle-derived magmatism that gave origin to the Mafic Complex of the southern section of the Ivrea-Verbano Zone and perfectly overlap the Permian hightemperature event recognized in the Kinzigite formation in the Finero section of the Ivrea-Verbano Zone.
Original languageEnglish
Publication statusPublished - 6 Sept 2017
EventGeosciences: a tool in a changing world (Congresso congiunto AIV, SGI, SIMP e SoGeI) - University of Pisa, Pisa, Italy
Duration: 4 Sept 20176 Sept 2017


ConferenceGeosciences: a tool in a changing world (Congresso congiunto AIV, SGI, SIMP e SoGeI)
Internet address


Dive into the research topics of 'Petrology and geochronology of the Loro Intrusive Complex (Ivrea-Verbano Zone)'. Together they form a unique fingerprint.

Cite this