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Some deep wells (1400–3000 m) have been drilled into the volcanic system of the Sabatini Mts., north of Rome, in search of high enthalpy geothermal fluids. Baccano caldera has formed over a carbonate structural high with a Quaternary volcanic cover, on the inside of a large graben that developed from the Upper Miocene and is characterized by a strong positive thermal anomaly. A spatially irregular Neogenic neoautochthon cycle, an allochthonous flysch complex (‘Sicilidi’ s.l.) and a Meso-Cenozoic ‘basal’ carbonate sequence were recognized in the sediments crossed by these wells below the volcanic cover. The observed structural setting can be correlated to that of analogous outcropping structures (Mt. Soratte) and shows a tensional tectonic phase overlying an older, mainly compressional phase. The stratigraphic and mineralogic analyses revealed important differences in the Trias, which is mainly calcareous in the western sector of the area and anhydritic in the eastern: the two facies at present seem to be tectonically brought closer to one another. The isotopic analyses all show values comparable to those of the sedimentary carbonate host rocks, suggesting limited circulation of the hydrothermal fluids. 18 O/ 16 O analyses on specimens in the most restrictive locations next to interfaces show a relatively larger extent of isotopic exchange with aqueous fluids. Fluid circulation, which is mainly extinct, seems to belong to a closed system. Two types of circulation have been recognized: the first of these is connected to the stratigraphic discontinuities (especially at the contact between the allochthonous flysch complex and the basal carbonate sequence) and is characterized by mainly K-feldspar and Sulphide-Sulphate mineralizations; the second circulation is tied to the fracture systems and is particularly widespread in the pyroclastic cover where it appears in the form of sulphate- and carbonate-rich dykes. This system seems to have undergone a mixing with surface waters.

The characteristics of wind erosion as the dominant process involved in eroding crater ejecta deposits on Mars are studied. Present-day crater formation in mid to high latitudes involves impact into some thickness of aeolian debris, while impact in the equatorial zone is more likely to involve target materials consisting of coarse-grained aeolian lag deposits or even bedrock. Latitudinal variation dominates differences in ejecta emplacement mechanisms and probably differences in patterns of wind erosion of ejecta and surrounding intercrater materials. Escarpments develop as the deposits are eroded back toward crater rims. Erosion only takes places at escarpment edges where surface roughness may be low enough to allow particle entrainment. Preferential preservation of ejecta emplaced in thick debris may occur. An empirical model developed for wind erosion of ejecta deposits in nonmantled areas suggests that removal of ejecta materials on the average is exceedingly slow. Results suggest high differential aeolian erosion rates that are a function of both grain sizes and large-scale surface roughness.

New results for the Colli Albani volcano (Roma, Italy) surveyed for the Geological Map of Italy at 1:50,000 scale (CARG Project), integrated with previous data, provide insights on caldera evolution. The Colli Albani, a quiescent volcano, became active at ∼600 ka. Eruptive compositions are consistently mafic ( 50 km 3 deposits), forming the Villa Senni Eruption Unit ignimbrites at ca. 355 ka, two edifices were built within the caldera: (1) The horseshoe-shaped Tuscolano-Artemisio (TA) composite edifice (or lithosome) consists of coalescing, peri-caldera, fissure-related scoriae cones interbedded with lava flows; the fissure system forms two segments controlled by regional fractures; (2) The steep-sided Faete stratovolcano (949 m a.s.l.) filled the caldera. The TA and Faete lithosomes partly interfinger and were emplaced at ∼350–260 ka. Their products indicate reduced eruption rates relative to the VL period and a change to effusive and mildly explosive eruptions. The most recent and still active phase of phreatomagmatic activity formed overlapping maars and tuff cones along the western and northern slopes of the volcano, collectively named Via dei Laghi composite lithosome. The Colli Albani caldera is poly-phase: (1) a piecemeal caldera is associated with large volume ignimbrites of the VL edifice; the present shape of the caldera is related to the Villa Senni eruption; 2) the TA composite edifice, erupted from peripheral-caldera fissures, is unrelated to explosive phases of caldera collapse: the TA final products cover a morphologically stable caldera wall. The peripheral fractures feeding the TA composite edifice are interpreted as volcano-tectonic structures activated during the late stage downsag of the caldera. Reduced eruption rates during the TA and the Faete stages (10 −1 km 3 /1 ka respect to >10 0 km 3 /1 ka for the VL edifice) suggest a reduced recharge of the magma chamber that may have induced prolonged deflation and downsagging of the caldera floor and the opening of outward dipping peripheral fractures. By this interpretation, the TA edifice represents the surface expression of ring dykes at depth. The absence of similar fissure-structures along the western caldera rim may relate to the deep geometry of the ring-faults dipping inward in those areas and therefore not favourably oriented for magma intrusion during a period of general subsidence. By contrast, the following and still active phreatomagmatic phase, that has emplaced the Via dei Laghi composite edifice, is located right on the western side of the caldera, and may therefore relate to resurgent conditions. Classical petrological and PERs (Pearce Elements Ratios) analyses indicate that lavas are co-genetic and show a differentiation trend up through stratigraphy driven by