ABSTRACT LXXV, April 2006 n.1:

Abstract - In this work we reconstruct the compositional zoning of the coronitic garnet developed between biotite and plagioclase in the Monte Mucrone metagranodiorite (Sesia Zone, Western Italian Alps) during the HP Alpine metamorphism, by using a modified segregation-dissolution model and supposing slow plagioclase resorption. Information on the rates of burial and exhumation of the rock (0.75 cm/year), on the garnet growth rate (~ 9 × 0^–17 cm/s) and on the evolution of the composition of the minerals (biotite, phengite, plagioclase, K-feldspar, Na-pyroxene) associated to the garnet, have been obtained. Furthermore, we have estimated that the minimum peak pressure recorded by the Monte Mucrone metagranodiorite is 16 kbar

Selma Russo, Daniela Cutrupia, Marcella Di Bella, Caterina Minutoli - High-pressure metamorphism in Southern Calabria, Italy: the Cardeto chlorite-garnet metapelites

Abstract - The Aspromonte Massif (Southern Calabria, Italy) consists of an Alpine crystalline nappe pile, belonging to the Southern Sector of the Calabrian Arc. The Aspromonte Unit, forming the bulk of the Massif, is overlain by the Stilo Unit and overlies, near Cardeto and Africo, phyllites and micaschists. Structural analysis on the Cardeto metapelites emphasized three deformation phases. Abundant “pin-prick” garnets characterize the fine-grained phyllites, porphyroblasts and “pin-prick” crystals are present in the micaschists. Garnets are almandine-rich with a low Mg content and variable amount of spessartine and grossular, depending on the rock composition. The porphyroblastic garnets are strongly zoned and exhibit distinctive bell-shaped Mn profiles typical of a prograde growth. The pin-prick garnets show the same composition as the rims of the porphyroblastic crystals of the same sample, suggesting a late stage growth with respect to the porphyroblasts. Phengitic white mica and chlorite composition suggest crystallization under relatively-high pressure conditions.
Physical conditions, inferred using chlorite-garnet geothermometer and modelled P-T pseudosections in the MnNCKFMASH system for chemically similar metapelites, suggest P in the range of 7.5-10 kbar, in the T range of 500-550°C. The widespread biotite-free chlorite+almandine assemblage suggests a crystallization of almandine prior to biotite, as happens in the Sanbagawa metamorphic region of Japan, where the chlorite, garnet, biotite+albite and biotite+oligoclase assemblages at increasing temperature, indicate a P/T ratio intermediate between the blueschist facies and the Barrovian greenschist facies conditions.
High pressure conditions have never been estimated in the Variscan metamorphism of the Southern Sector of the Calabrian Arc, which, instead, is characterized by medium-low P/T ratio. Only the Aspromonte Unit, tectonically overlying the Cardeto metamorphics, shows a pervasive Alpine overprint, which is characterized by a higher P/T ratio than that of the Variscan metamorphism. Consequently, we assume that the Cardeto metapelites were probably affected by an Alpine metamorphic event.
Owing to the similar structural position, the Cardeto rocks could represent the Calabrian part of the Mandanici Unit, which extensively outcrops in the nearby Peloritani Mountains, that in Calabria has been overprinted by Alpine effects, but no structural or mineralogical relicts which support this interpretation have been observed. More probably, they represent a distinct Alpine tectonic unit which have experienced a relatively-high pressure Alpine (?) metamorphism and that in the Peloritani Mountains was removed from within the tectonic pile during a syn-orogenic extension episode.

Lorenzo Fedele, Vincenzo Morra, Annamaria Perrotta, Claudio Scarpati - Volcanological and geochemical features of the products of the Fiumicello eruption, Procida island, Campi Flegrei (southern Italy)

Abstract - A volcanological and geochemical characterization of the products of the Fiumicello eruption is here proposed. The volcanological features of the deposits, representing both a “proximal” and a “distal” facies, suggest that the eruption dynamics were quite similar to those of many other Campi Flegrei events, being characterized by both purely magmatic and phreatomagmatic phases. The physical parameters of the eruption, like its relatively low magnitude, the height of the eruption column and the dispersion of the products, are still comparable to those of many other events which characterized Campi Flegrei’s volcanological evolution.
The mafic composition of the products of the Fiumicello eruption is rather unusual within the context of the Campi Flegrei district, largely dominated by highly evolved products. Therefore, the study of the products of this eruption gives an almost unique opportunity to investigate Campi Flegrei’s plumbing system. Anyway, major- and trace element geochemistry, as well as mass-balance results, show that Fiumicello products can not be considered as representative of primary melts compositions.
The geochemical vertical variations observed within the products of the eruption suggest that the Fiumicello event was fed by a density stratified magma chamber. The existence of such reservoir structures has already been proposed for other Campi Flegrei eruption and, therefore, their development seems to be a very important process in the framework of the evolution of the Campi Flegrei magmatic system.

Paolo Orlandi, Gianni Cortecci, Giuseppe Protano and Francesco Riccobono - Mineral assemblages, stable isotopes and fluid inclusions in ore veins from the Macigno Formation at Calafuria (Livorno Mountains, northern Tuscany, Italy)

Abstract - The present paper deals with an integrated geological, mineralogical and geochemical study on mineralized faults and fractures recognized in the Macigno Formation at Calafuria in the Livorno Mountains of northern Tuscany. In the field, two main different systems of faults were recognized: an earlier one related to a compressive phase with NE-SW and N-S trending faults, and a younger one related to a relaxation phase with NW-SE trending faults. They distinguish for specific mineral assemblages, consisting mainly of quartz in the former, and barite-marcasite-pyrite in the latter. Minerals were analyzed for fluid inclusions and isotopic composition. Data on fluid inclusions indicate that three main mineralizing episodes affected the fault systems. In the first episode, the fluids deposited quartz in the fault systems related to the compressive phase. The second episode was the main one, and led to the deposition of euhedral quartz in the NE-SW faults, and barite, maracasite and pyrite essentially in the N-S and NW-SE faults. The fluid evolution ended with the deposition of calcite, dolomite and a series of supergene minerals originated by alteration of Fe-sulfides.
The sulfur isotopic composition of minerals (–6.3 to 25.1‰) would seem to exclude a magmatic origin of the sulfur, favoring instead a sedimentary origin. Moreover, a temperature of about 400°C is estimated by sulfur isotope thermometry for the second stage of mineralization. Owing to pressure effects, the homogenization temperature given by the fluid inclusions for this stage of mineralization is considerably lower that the isotopic one.
A lithostatic pressure of 125 MPa is estimated for the barite and sulfide mineralization, this corresponding to a depth of 5 Km. Finally, a post-Middle Pliocene age is proposed for the ore veins at Calafuria, that may have formed during tectonic relaxation events from hydrothermal fluids rich in CO₂ and H₂S, as are observed in the Larderello geothermal area at present.

ANGELO PECCERILLO - Carbonatites vs. carbonated rocks in central Italy. A reply to comments by Bell and Kjarsgaard

Abstract - In two previous papers (Peccerillo, 1998, 2004), I raised doubts about the widely accepted idea that the carbonate-rich pyroclastic rocks from the Intra-Apennine Province (IAP) are carbonatites. This provoked a late but considerable reaction from carbonatite scholars, including people unfamiliar with the subject and with the complex magmatic setting of central-southern Italy. Bell and Kjarsgaard do not give an answer to my questions, show a lack of knowledge of the subject in hand, and reveal scarce consideration for results of previous work. In my reply, I briefly discuss the few scientific aspects raised by Bell and Kjarsgaard that are worthy of note, and highlight some philosophical and ethical aspects of their writing. I reiterate my objections, which remain unanswered, and conclude that further discussion on IAP rocks will have my consideration only if future comments, if any, will provide an answer to my questions and will lead to an advancement in our understanding of central Italy magmatism and its geodynamic significance.