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The least evolved Jurassic Ferrar tholeiites from southern Prince Albert Mountains (Antarctica) are characterized by the occurrence of orthopyroxene (opx), a mineralogical feature virtually absent in the tholeiites from the large igneous provinces of Karoo (South Africa) and Parana (Brazil). Petrography suggests that opx is the early phase in the sequence of crystallization and mineral chemistry indicates that it is in equilibrium with the host rock. In general, MELTS modeling predicts that opx is the liquidus phase in the Ferrar tholeiites with MgO higher than ~7 wt% at P= 1.5-5 kbar, [H.sub.2]O = 0-1 wt% and [Florin.sub.O2] = QFM - 1 log unit conditions. MELTS results also show that the early crystallization of opx is primarily controlled by high Si[O.sub.2] and high Si[O.sub.2]/CaO, chemical characteristics typical of the Ferrar tholeiites, but not shown by the Karoo and Parana analogs with similar MgO content. Major element geochemistry of the least evolved Ferrar tholeiite has been modeled through fractional crystallization and fractional crystallization coupled with crustal assimilation processes, starting from natural peridotite-derived experimental melts. Mass balance and MELTS modeling support the argument that theoretical magma compositions suitable to be primary to the least evolved Ferrar tholeiites are compatible with hydrous ([H.sub.2]O = 0.3-0.5 wt%) and anhydrous melts obtained at 10-15 kbar by high melting degrees (>25%) of fertile and depleted spinel lherzolites, respectively, and later contaminated by the high-grade metamorphic rocks from the Victoria Land crystalline basement. The genesis of primary Ferrar tholeiites does not necessarily reflect the generally assumed depleted source mantle being also compatible with a fertile one.

New geochemical and isotopic data on volcanic rocks spanning the period ~75-50 ka BP on Ischia volcano, Italy, shed light on the evolution of the magmatic system before and after the catastrophic, caldera-forming Monte Epomeo Green Tuff (MEGT) eruption. Volcanic activity during this period was influenced by a large, composite and differentiating magmatic system, replenished several times with isotopically distinct magmas of deep provenance. Chemical and isotopic variations highlight that the pre-MEGT eruptions were fed by trachytic/phonolitic magmas from an isotopically zoned reservoir that were poorly enriched in radiogenic Sr and became progressively less radiogenic with time. Just prior to the MEGT eruption, the magmatic system was recharged by an isotopically distinct magma, relatively more enriched in radiogenic Sr with respect to the previously erupted magmas. This second magma initially fed several SubPlinian explosive eruptions and later supplied the climactic, phonolitic-to-trachytic MEGT eruption(s). Isotopic data, together with erupted volume estimations obtained for MEGT eruption(s), indicate that >5-10 [km.sup.3] of this relatively enriched magma had accumulated in the Ischia plumbing system. Geochemical modelling indicates that it accumulated at shallow depths (4-6 km), over a period of ca. 20 ka. After the MEGT eruption, volcanic activity was fed by a new batch of less differentiated (trachyte-latite) magma that was slightly less enriched in radiogenic Sr. The geochemical and Sr-Nd-isotopic variations through time reflect the upward flux of isotopically distinct magma batches, variably contaminated by Hercynian crust at 8-12 km depth. The deep-sourced latitic to trachytic magmas stalled at shallow depths (4-6 km depth), differentiated to phonolite through crystal fractionation and assimilation of a feldspar-rich mush, or ascended directly to the surface and erupted. Keywords Ischia volcano * Magmatic plumbing system * Radiogenic isotopes * Geothermometry * Feldspar assimilation * Caldera collapse, Introduction Caldera-forming eruptions are among the most destructive natural phenomena on the planet and can catastrophically disperse huge volumes of fragmented magma across large areas in hours to days. Understanding [...]

An analysis of trace element abundances and Sr-Nd-Pb isotopic compositions was conducted for andesitic sills and andesitic basalt and lavas of the Jurassic Ferrar Magmatic Province, Antarctica and Prince Albert Mountains. The objective was to prove that the primary Ferrar basalts were not obtained from a depleted source mantle but may instead be obtained from an enriched mantle with Dupal isotopic signature. A petrological model is proposed whereby Ferrar magmas were produced through high degrees of melting of an E-type MORB.