Metamorphic, metasomatic and intrusive xenoliths of the Colli Albani volcano and their significance for the reconstruction of the volcano plumbing system
A. A. De Benedetti, E. Caprilli, F. Rossetti, G. Giordano, 2010. "Metamorphic, metasomatic and intrusive xenoliths of the Colli Albani volcano and their significance for the reconstruction of the volcano plumbing system", The Colli Albani Volcano, R. Funiciello, G. Giordano
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This paper analyses the xenoliths found in the phreatomagmatic products of the most recent Via del Laghi maar field at Colli Albani volcano in order to investigate the nature of the substratum and its interaction with the magmatic system. The pre-volcanic sedimentary xenoliths are from the same rock formations that form the pre-orogenic Mesozoic–Cenozoic carbonatic pelagic succession cropping out in the nearby Apennine mountain belt, and the Pliocene post-orogenic marine sedimentary succession. Along with the sedimentary xenoliths, a large variety of thermo-metamorphic, metasomatic and magmatic xenoliths are present. Skarn xenoliths have been studied to estimate peak metamorphic P–T conditions and assess the role of fluids during prograde and retrograde metamorphism. The presence of hydrous minerals such as phlogopite and amphibole and the carbonatic nature of the substratum suggest a binary H2O–CO2 mixture as the dominant fluid. Microscale wollastonite filling fractures indicates a temporal link between fracturing and fluid infiltration. The occurrence of retrograde hydrous textures superimposed on anhydrous associations indicates at least a two step process: metamorphism with a T peak at dry conditions (CO2 saturated), followed by fracturing of the substratum in the late stage, allowing abundant aqueous fluids to penetrate the thermally modified rocks. A significative amount of rare earth minerals crystallized in the late stage.
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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.