Magma Plumbing System at a Young Back‐Arc Spreading Center: The Marsili Volcano, Southern Tyrrhenian Sea

• Published in: Geochemistry, geophysics, geosystems : G3 Vol. 19; no. 1; pp. 43 - 59
• Main Authors: Trua, T., Marani, M. P., Gamberi, F.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 01.01.2018
• Subjects: Accretion; back‐arc spreading; Basalt; Crustal accretion; Crustal structure; Crystals; Decompression; Frameworks; Lava; Magma; Mantle; Melting; Modelling; petrological model; Plagioclase; Plumbing; plumbing system; Porosity; Ridges; Seafloor spreading; Spreading centres; Subduction; Tyrrhenian; Volcanoes; Tyrrhenian Sea
• ISSN: 1525-2027; 1525-2027
• DOI: 10.1002/2017GC007151

Although spreading rate is commonly taken as a proxy for decompression mantle melting at mid‐ocean ridges (MORs), magmatism at back‐arc spreading centers (BASCs) is further influenced by the subduction‐related flux melting of the mantle. These regions consequently show a diversity of crustal structures, lava compositions, and morphologies not typically found in MORs. Here we investigate the crustal plumbing system of the small‐scale, Marsili back‐arc spreading center of the Southern Tyrrhenian Sea using plagioclase data from a wide spectrum of lavas (basalts to andesites) dredged from its summit and flanks. We employ petrological modeling to identify the plagioclase populations carried in the individual lavas, allocate them to plausible magmatic components present within the plumbing system, and trace the processes occurring during magma ascent to the surface. The properties of the system, such as mush porosity and abundance of the melt bodies, vary from one magma extraction zone to another along the BASC, evidencing the local variability of melt supply conditions. The plagioclase crystals document a range of relationships with the host lavas, indicating magma extraction from a composite, vertically extensive mush and melt‐lens system resembling that of MORs. At the same time, however, in small BASCs, such as in the case of the Marsili Basin, crustal accretion and resulting morphology are significantly influenced by the three‐dimensional setting of the basin margins. This is an important deviation from the conventional model based on the linear continuity and essentially two‐dimensional framework of MORs. Key Points Plagioclase crystals offer a unique insight into the plumbing system of the youngest back‐arc spreading center of the Tyrrhenian Sea Crustal magma storage is in the form of melt lenses and dykes vertically extended in a mush domain with locally variable crystallinity In some aspects, crustal accretion processes in the Marsili spreading center resemble those operating in mid‐ocean ridges