Ultrapotassic rocks

Ultrapotassic rocks from Tuscany have a lamproitic composition (see Appendix for nomenclature of potassic rocks). Older lamproites (14 Ma) occur at Sisco, Corsica. Kamafugitic rocks make up a few monogenetic centres in the internal zones of northern-central Apennines (Umbria, Latium, Abruzzi), and have been found at Vulsini and as ejected blocks in pyroclastic deposits at Colli Albani (Federico et al. 1994). Roman-type potassic and ultrapotassic rocks (KS and HKS) form the bulk of magma-... 

This is part of the belt of potassic and ultrapotassic rocks running from northern Latium to the Neapolitan area, which was defined as the Roman Comagmatic Region by Washington (1906). The Roman Province (or... 

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... 

This province is characterised by the close association of KS and HKS rocks, showing diverse geochemical and isotopic signatures. Some low-potassium mafic rocks falling in the calc-alkaline compositional field have been also found. Potassic rocks display ratios of some incompatible trace elements such as Ba/La, and radiogenic isotope signatures that are close to those of the Neapolitan volcanoes (Vesuvio, Campi Flegrei, Ischia). On the contrary, ultrapotassic rocks resemble the Colle Albani and other Roman volcanoes. Therefore, the Ernici-Roccamonfina zone is characterised by the coexistence of Roman-type and Campanian-type rocks. 

Major element studies (Cundari 1979 Conticelli et al. 1997 and references therein) have shown that the Sabatini volcanics consist almost entirely of undersaturated ultrapotassic rocks, ranging from tephrite to phonolite (Figs. 4.2, 4.15), with dominant phonotephrites. A few trachytes and latites have been erupted locally (Morlupo and Vigna di Valle lava flows). 

Variation diagrams of major and trace elements vs. MgO at Colli Albani (Fig. 4.19) show a positive correlation for CaO, TiC>2, FeOtotai and ferro-magnesian trace elements (Cr, Ni, Co, etc.), negative correlations for Na20, K2O, AI2O3 and incompatible elements (Th, La, Ta, etc.), and a bell shaped trend for P2O5. Incompatible elements show smooth inter-element positive trends (Fig. 4.19g). The pre-caldera lavas seem to define different trends on some major and trace element variation diagrams, especially on plots of incompatible element vs. incompatible element ratios (Fig. 4.19h). REE and incompatible element patterns have shapes that are similar to those for other ultrapotassic rocks from the Roman Province (Fig. 4.20). 

Roccamonfina 0.58 to 0.1 Potassic rocks generally younger than ultrapotassic rocks - Stravolcano with a main central caldera and eccentric cones, formed of alternating lava flows and pyroclastic products with a mafic to felsic subalkaline to alkaline potassic (KS) and ultrapotassic (HKS) composition. 

The most important eruptive centres include the pyroclastic flows of Pa-trica and the cones of Tecchiena, Celletta, Colle Castellone, Borghetto, Pofi, Villa Santo Stefano and Giuliano di Roma. Most of these centres consist of mafic ultrapotassic rocks potassic and low potassic basalts occur at Villa Santo Stefano and in a few places south of Ceccano (Fig. 5.2). 

An important feature of magmatism in Campania is that the Campi Flegrei mafic rocks are moderately potassic in composition but have very similar concentrations and ratios of several incompatible elements as the ultrapotassic rocks from Somma-Vesuvio these, however, contain higher concentrations of K and Rb (e.g. Peccerillo 2001). In other words, the positive correlation between potassium and incompatible elements observed in other Italian volcanic districts (e.g. Emici and Roccamonfma) is not so evident in Campania. 

The predominance in central Italy of ultrapotassic rocks, possibly associated with carbonatites, and the absence of calc-alkaline activity. A similar association occurs in the Toro-Ankole igneous province (western branch of the East Africa Rift Bailey and Collier 2000), classically believed to have developed above mantle plumes. 

Cellai D, Conticelli S, Menchetti S (1994) Crystal-chemistry of clinopyroxenes from potassic and ultrapotassic rocks in central Italy implications for their genesis. Contrib Mineral Petrol 116 301-315 Cello G, Mazzoli S (1999) Apennine tectonics in southern Italy. A review. J Geo-dyn 27 191-211... 

Di Battistini G, Montanini A, Zerbi M (1990) Geochemistry of volcanic rocks from southeastern Montiferro. Neues Jahrb Mineral Abh 162 35-67 Di Battistini G, Montanini A, Vemia L, Bargossi GM, Castorina F (1998) Petrology and geochemistry of ultrapotassic rocks from the Montefiascone volcanic complex (Central Italy) magmatic evolution and petrogenesis. Lithos 43 169-195... 

Foley SF, Venturelli G, Green DH, Toscani L (1987) The ultrapotassic rocks characteristics classification, and constraints for petrogenetic models. Earth Sci Rev 24 81-134... 

Conticelli S., Francalianci L., Manetti P., Cioni R., and Sbrana A. (1997) Petrology and geochemistry of the ultrapotassic rocks from the Sabatini volcanic district, central Italy the role of evolutionary process in the genesis... 

Castor SB (2008) The Mountain Pass rare-earth caibonatite and associated ultrapotassic rocks, California Can Mineral 46 779-806... 

Bourzac K (2011) The rare-earth crisis. MIT Technol Rev Mag May/June 2011 Canadian Chamber of Commerce (2012) Economic policy series, pp 5-6. Apr 2012 Canadian Institute of Mining, Metallurgy and Petroleum (2015) htq) //www.cim.org/en/RareEarth/ Home/GlobalReeProduction.aspx. Accessed May 2015 Castor SB (2008) The mountain pass rare earth carbonatite and associated ultrapotassic rocks, California. Can Mineral 46 779-806... 

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