Mattia Gilio, PhD

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Mattia Gilio

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My research is field-based and process-oriented and focusses on subduction zone processes, fluid rock interactions and earthquakes dynamics and triggering processes within HP to UHP rocks from orogenic belts as the Western Alps and the Central Scandinavian Caledonides.

I am currently working on stress measurement on host-inclusion systems in natural samples from various HP and UHP localities in the Western and Central Alps (Brossasco-Isasca Unit, Lago di Cignana Unit, Alpe Arami) and from the Western Gneiss Region (Norway) and the Seve-Nappe Complex (Sweden). In my work, I will test new methods of elastic geobarometry of host-inclusion systems and compare it to classic geothermobarometry and thermodynamic modelling. My aim is to reconstruct the P-T-t-σ histories of major HP to UHP terranes, with major implications on differential stresses in subduction zones, depths of burial and earthquake triggering mechanisms.

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Plate Interface

The plate interface is a 1-to-10 km thick layer at the boundary between the subducting plate and the mantle wedge where deformation, fluid fluxed and mass transfer are concentrated. Processes occurring at the plate interface rule the rheology and the mechanical properties of subduction zones and the exchange between fluid and rocks and the composition of the fluid released into the mantle wedge and thus recycled into arc lavas. Furthermore, this zone might be utilized as channel to exhume high to ultrahigh pressure rocks and high magnitude subduction earthquakes occur within, or just below, this low velocity zone. According to geophysical studies, the plate interface consists of the top section of the altered oceanic crust, or a mixing zone of crustal- and mantle-derived material, or serpentinites. My petrological and geochemical studies of ophiolites form the Western Alps helps to reconstructs the architecture and lithologies of deep plate interface settings.

Serpentinites

Serpentinites are sections of lithospheric mantle, hydrated at the seafloor or during subduction. Isotopic (Pb, Sr and B) and trace element (B, Be, As, Sb, U, Th) signatures of serpentinites are useful geochemical tools to assess element exchange and fluid-rock interactions in subduction zone settings. They help unravel geological history, timing of accretion and tectonic evolution of subduction serpentinites and associated meta-oceanic crust. Sedimentary-derived fluid influx within HP plate interface environments strongly enriches serpentinites in As, Sb, Be, B, U and Th and resets their B, Sr and Pb isotopic compositions. This HP metasomatic signature is preserved during exhumation and/or released at higher PT through de-serpentinization, fuelling partial melting in the sub-arc mantle and recycling such fingerprint into arc magmas. My study focuses on the subduction recrystallization, geochemical diversity and fluid-rock interaction recorded by ophiolitic high- to ultra-high pressure (HP, UHP) Alpine serpentinites from the subducting oceanic plate.

Tectonic significance of serpentinites

The role of serpentinites in the dynamics of subduction zones is linked to their rheological properties. Recent rheological experiments showed serpentinites display a very weak response to deformation, acting as a lubricant in subduction zones (T∼500-600 °C). Despite their relative scarcity on Earth’s surface, serpentinites are found in every major tectonic setting involving continental rifting, slow to ultra-slow spreading ridges, strike-slip faults and subduction zones. They are also often associated with deep-subduction earthquakes, thought to be triggered by serpentine dehydration reactions. As such, serpentinites weaken the otherwise stiff eclogitic oceanic crust, allowing plastic flow and largely reducing friction at the plate interface.

Subduction earthquakes & pseudotachylytes

Subduction zones are main earthquake factories on Earth. While geophysical studies and laboratory experiments provide most information on subduction earthquakes and their mechanics, field-based studies describing earthquake sources exhumed from deep subduction environments are still few. To date, fluid overpressure associated with mineral dehydration is the widely-favoured trigger of subduction earthquakes, especially in serpentinized lithospheric mantle and in hydrated low-velocity layers atop the slabs. Pseudotachylytes are the fossil remnants of deep subduction earthquakes and form by friction heating along the fault plane. I study pervasive co-seismic fracturing and pseudotachylytes formed during eclogite-facies conditions in subducted Alpine ophiolites to gain insight on earthquake-triggering mechanisms in subduction zones.

RECENT PUBLICATIONS (2014-2016)

Scambelluri M., Bebout G.E., Belmonte D., Gilio M., Campomenosi N., Collins N., Crispini L. (2016). Carbonation of subduction-zone serpentinite (high-pressure ophicarbonate; Ligurian Western Alps) and implications for the deep carbon cycling. Earth and Planetary Science Letters 441, 155-166. DOI: 10.1016/j.epsl.2016.02.034

Scambelluri M., Cannaò E., Gilio M., Godard M. (2015). Petrologic and geochemical role of serpentinite in subduction zones and plate interface domains. Rendiconti Online della Società Geologica Italiana 37, 61-64. DOI: 10.3301/ROL.2015.177

Gilio M., Clos F., van Roermund H.L.M. (2015). The Friningen Garnet Peridotite (central Swedish Caledonides). A good example of the characteristic PTt path of a cold mantle wedge garnet peridotite. Lithos 230, 1-16. DOI: 10.1016/j.lithos.2015.05.003

Clos F., Gilio, M., van Roermund H. L.M. (2014). Fragments of deeper parts of the hanging wall mantle preserved as orogenic peridotites in the central belt of the Seve Nappe Complex, Sweden. Lithos 192, 8-20. DOI: 10.1016/j.lithos.2014.01.004