Maurizio Sonnino

Temporal evolution of a three component system: the island of Lipari (Aeolian Arc, southern Italy)

The volcanic products from Lipari define an evolutionary trend with a high gradient of K-enrichment, similar to the calc-alkaline to potassic volcanism of other islands in the Aeolian arc. Stratigraphic reconstruction of the island based on field and geochronological data indicate that the volcanic activity can be subdivided in two stages. The first stage, from 223 to 42 ka, consists of six eruptive cycles and is characterized by basalts and basalt-andesites showing progressive increase in both SiO2 and K2O contents with time. The second stage consists of four cycles erupted since 42 ka and is marked by an apparent rejuvenation of the geochemical system with the appearance of the first rhyolitic products. Fractional crystallization, assimilation and mixing models suggest that the geochemistry of Lipari volcanism evolved with time by a complex interplay between two mantle-derived components, one sub-alkaline and the other alkaline, in addition to crustal melts and/or crustally-derived materials. A petrogenetic model in which fractional crystallization was subordinate to mixing best fits the geochemical data and petrographic observations of macro- and microscopic features. Melts from the crustal and mantle end-members are almost always present in the system but the relative proportions appear to vary with time. The sub-alkaline mantle component (source of Tyrrhenian tholeiites) is an important contributor to the early evolution of the volcanism in Lipari; input from the alkaline mantle component (source of the Roman Comagmatic Province) increases with time, and the crustal component becomes dominant in the later activity. The preferred petrogenetic model for the temporal evolution of the volcanic system in Lipari involves melting initially caused by an increase in the thermal input related to the opening of the Tyrrhenian Sea and/or to subduction processes. The quick rise of the isotherms and almost contemporaneous melting of source materials with different compositions favored complex mixing during ascent of the melts.

Compositional and Geochemical Signatures for the Sedimentary Evolution of the Middle Triassic-Lower Jurassic Continental Redbeds from Western-Central Mediterranean Alpine Chains

Compositional and chemical analyses suggest that Middle Triassic–Lower Liassic continental redbeds (in the internal domains of the Betic, Maghrebian, and Apenninic chains) can be considered a regional lithosome marking the Triassic-Jurassic rift-valley stage of Tethyan rifting, which led to the Pangaea breakup and subsequent development of a mosaic of plates and microplates. Sandstones are quartzose to quartzolithic and represent a provenance of continental block and recycled orogen, made up mainly of Paleozoic metasedimentary rocks similar to those underlying the redbeds. Mudrocks display K enrichments; intense paleoweathering under a hot, episodically humid climate with a prolonged dry season; and sediment recycling. Redbeds experienced temperatures in the range of 100°–160°C and lithostatic/tectonic loading of more than 4 km. These redbeds represent an important stratigraphic signature to reconstruct a continental block (Mesomediterranean Microplate) that separated different realms of the western Tethys from Middle-Late Jurassic to Miocene, when it was completely involved in Alpine orogenesis.

Provenance signatures for the Miocene volcaniclastic succession of the Tufiti di Tusa Formation, southern Apennines, Italy

The Tufiti di Tusa Formation, a siliciclastic turbidite system of lower Miocene age in southern Italy, is mainly composed of volcaniclastic and quartzolithic sandstones interbedded with mudrocks. Sandstones are subdivided into four distinctive petrofacies, evolving from quartzolithic to volcaniclastic lithofeldspathic and feldspatholithic, reflecting detrital evolution from growing orogen (quartzolithic petrofacies) to active volcanism (volcaniclastic petrofacies). The mineralogical composition of the associated mudrocks is predominantly characterized by phyllosilicates, mainly illite/smectite mixed layers (I/S R1 associated with minor amounts of I/S R0 in the lower part of the succession, and I/S R3 in its upper part), together with illite, detrital micas and chlorite, and minor amounts of chlorite/smectite mixed layers and kaolinite, in addition to quartz, calcite and feldspars. The most abundant phyllosilicates are I/S mixed layers, 10-A minerals (illite and micas) and chlorite, while kaolinite and chlorite–smectite mixed layers are present as a few per cent or in trace amounts. X-ray diffraction patterns show the occurrence of the ordered I/S R1 mixed layers in most samples but, at the top of the succession, some samples are characterized by I/S R3 mixed layers, whilst in the lower part of the succession I/S R1 is associated with a lower amount of I/S R0. These features suggest that the Tufiti di Tusa Formation experienced a medium diagenetic grade, and the occurrence of I/S R3 could be explained by K-availability in samples in the upper part of the succession. The lithic fragments in sandstones are metasedimentary rocks of Palaeozoic age, and andesite to dacite volcanic rocks of early Miocene age. The associated mudrocks also contain trace element ratios (Cr/V, Y/Ni, La/Sc, Th/Sc, Th/Co, Th/Cr, Cr/Th and Eu/Eu*) consistent with a provenance containing intermediate to silicic sources with scarce or absent basic rocks. The chemical index of alteration (63.2 to 71.6) suggests a moderate degree of weathering in the source. Furthermore, the K/Cs ratios of sediments confirm likely moderate rather than intense weathering. The index of compositional variability (ICV) values (from 1.2 to 2.5) are high enough to suggest the mudrocks are first-cycle sediments with little recycling. The Al–Ti–Zr diagram and the Th/Sc v. Zr/Sc plot indicate poor sorting and rapid deposition of the sediments. Detrital and sedimentary evolution of the Tufiti di Tusa Formation provides constraints, in terms of relations between a growing orogenic system and active volcanism in the Central Mediterranean, to contribute to geodynamic and palaeogeographic reconstructions of the earliest collision in the southern Apennines region.