Geochemistry, isotopes and mineral chemistry of the Colli Albani volcanic rocks: constraints on magma genesis and evolution
S. Conticelli, E. Boari, R. Avanzinelli, A. A. De Benedetti, G. Giordano, M. Mattei, L. Melluso, V. Morra, 2010. "Geochemistry, isotopes and mineral chemistry of the Colli Albani volcanic rocks: constraints on magma genesis and evolution", The Colli Albani Volcano, R. Funiciello, G. Giordano
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The Colli Albani volcano belongs to the Roman Magmatic Province and is characterized by strongly silica undersaturated leucite-bearing ultrapotassic rocks. Melilite-bearing leucititic lavas, beside tephritic to tephritic phonolitic ignimbrites, were erupted during the pre-caldera (Vulcano Laziale) period. The post-caldera phase opened with magmas erupted from different feeding systems, with melilite-bearing leucitites in the early phases followed by tephritic and phonolitic tephritic lavas. The late-stage activity (i.e. the Via dei Laghi period) is characterized by hydromagmatic tuffs with small juvenile fragments that prevent a clear compositional definition of the magma triggering the eruptions. Despite their mineralogical and compositional similarities, the Vulcano Laziale period (pre-caldera) has significantly higher levels of incompatible trace elements and 87Sr/86Sr isotopes than found in magmatic rocks erupted after the caldera formation. Pre- and post-caldera parental magmas are considered to be significantly different from each other and generated within a metasomatized upper mantle under different degrees of partial melting. Crustal-derived carbonate-rich metasomatism is thought to have affected the mantle wedge of the Italian peninsula. Melting of pelitic sediments with different amounts of CaCO3 is considered the source of the metasomatic agents, which are able to re-fertilize the lithospheric upper mantle. Partial melting of this modally metasomatized lithospheric mantle under high XCO2 produced the strongly silica undersaturated ultrapotassic magmas observed at the Colli Albani volcano. A second-order differentiation process occurs at shallow levels, with fractional crystallization and crustal assimilation of wall rock (AFC), locally changing the compositions of magmas and producing several differentiation pathways that have given rise to the geochemical and petrological complexity of the Colli Albani volcano. Assimilation of carbonate sediments and silicoclastic sedimentary lithologies also occurred coevally, suggesting the existence of several separate magmatic reservoirs at shallow levels, possibly at different depths and surrounded by different sedimentary formations.
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The Colli Albani volcano (also Alban Hills volcano) is the large quiescent volcanic field that dominates the Roman skyline. The Colli Albani is one of the most explosive mafic calderas in the world, associated with intermediate to large volume ignimbrites. At present it shows signs of unrest, including periodic seismic swarms, ground uplift and intense diffuse degassing, which are the main short-term hazards. New studies have discovered deposits related to previously unknown pre-Holocene and Holocene volcanic and phreatic activity. In the fourth Century B.C.E. Roman engineers excavated a tunnel through the Albano maar crater wall to keep the lake from breaching the rim and flooding the surrounding countryside, events that had previously destroyed this region several times.
The Colli Albani Volcano contains 21 scientific contributions on stratigraphy, volcanotectonics, geochronology, petrography and geochemistry, hydrogeology, volcanic hazards, geophysics and archaeology, and a new 1:50 000 scale geological map of the volcano. The proximity to Rome and the interconnection between volcanic and human history also make this volcano of interest for both specialists and non-specialists.