MAFIC INCLUSIONS IN THE SILICA-RICH ROCKS OF THE TOLFA-CERITI-MANZIANA VOLCANIC DISTRICT (TUSCAN PROVINCE, CENTRAL ITALY) - CHEMISTRY AND MINERALOGY

A chemical and mineralogical study of magmatic inclusions in the silic a-rich rocks of the Tolfa-Ceriti-Manziana sector (Tuscan Province, Cen tral Italy) shows that they can be grouped according to their degree o f alkalinity. We distinguish: TCM latites (TCML) with an alkaline-pota ssic affinity; Ceriti latites (CL) with calc-alkaline affinity; and Ma nziana shoshonites and latites (MS-ML) with an affinity intermediate b etween alkaline and subalkaline. The latter are hybrid rocks originati ng from the mixing of two magmas with slightly different geochemical a ffinities. These magmas may represent liquids derived by partial melti ng of a heterogeneous mantle, metasomatized by a crustal source. The m ost alkaline magmas (TCML) are associated with the largest degree of m etasomatism which, if more pronounced, could lead to the production of the potassic magmas of the Roman Province.