Vico volcano

Figure 7. Two examples of whole-rock isochrons, (a) Isochron obtained on a lava nnit of the Vico volcano (Central Italy) (Villemant and Flehoc 1989). (b) Isochron defined by glass and groundmass analyses of the Laacher See phonolite (Bonidon et al. 1994). In both examples, differentiation occurred shortly before eraption since calculated ages are indistinguishable from eraption ages.

Villemant B, Flehoc C (1989) U-Th fractionation by fluids in K-rich magma genesis the Vico volcano, Central Italy. Earth Planet Sci Lett 91 312-326... 

Fig. 4.10. Schematic geological map of Vico volcano. Simplified after Perini et al.

The Emici and Roccamonfina magmas exhibit peculiar compositional characteristics in terms of their very variable geochemical and isotopic signatures for potassic to ultrapotassic mafic rocks. These are not encountered in other potassic volcanoes of central Italy (i.e. Roman and Campanian provinces, with the possible exception of Vico volcano), where coexisting KS and HKS rocks have different potassium and incompatible trace element abundances but exhibit similar incompatible element ratios and radiogenic isotope signatures (Peccerillo 1999, 2002). 

Barbieri M, Peccerillo A, Poli G, Tolomeo L (1988) Major, trace element and Sr isotopic composition of lavas from Vico volcano (Central Italy) and their evolution in an open system. Contrib Mineral Petrol 99 485-497... 

Villemant B, Flehoc C (1989) U-Th fractionation by fluids in K-rich magma genesis the Vico volcano, Central Italy. Earth Planet Sci Lett 91 312-326 Vollmer R (1976) Rb-Sr and U-Th-Pb systematics of alkaline rocks the alkaline rocks from Italy. Geochim Cosmochim Acta 40 283-295 Vollmer R (1977) Isotopic evidence for genetic relations between acid and alkaline rocks in Italy. Contrib Mineral Petrol 60 109-118 Vollmer R (1989) On the origin of the Italian potassic magmas. A discussion contribution. Chem Geol 74 229-239... 

Barton M (1979) A comparative study of some minerals occnrring in the potassium-rich alkaline rocks of the Leucitite Hills, Wyoming, the Vico Volcano, Western Italy, and the Toto-Ankole Region, Uganda. N Jahrb Mineral Abh 137 113-134... 

Whole rock U-Th isochrons can also provide an age for the differentiation process, but they are rare because of the difficulty of fractionating the U/Th ratio through crystallization of major minerals. In the two reported examples (Laacher See phonolites, and Vico ultrapotassic volcanics), whole-rock isochrons show that differentiation occurred shortly before eruption. A similar conclusion was reached in the case of the Longonot volcano (Kenya), whose trachytes define the only reported ( Ra)/Ba-(230Th)/Ba whole-rock isochron. 

Latium Province) defined here only includes Vulsini, Vico, Sabatini and Colli Albani volcanoes. Potassic rocks (KS) basically consist of trachyba-salts, latites and trachytes ultrapotassic rocks (HKS) are represented by... 

Like other Roman volcanoes, the Vico pyroclastic rocks contain xeno-liths of various origin, including bedrock fragments, intrusive equivalents of lavas, and cumulate rocks. These xenoliths often contain exotic minerals, such as Zr-Ti-Th-U-REE rich phases (e.g. britholite, baddelyite, and pyrochlore), which have been interpreted to be the result of deposition from late-magmatic fluids rich in incompatible elements (e.g. Della Ventura et al. 1999). 

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