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Introduction
Publications
Publications (186)
Much of the long-term carbon cycle in solid earth occurs in subduction zones, where processes of devolatilization, partial melting of carbonated rocks, and dissolution of carbonate minerals lead to the return of CO2 to the atmosphere via volcanic degassing. Release of COH fluids from hydrous and carbonate minerals influences C recycling and magmati...
The cause of intermediate-depth (50–300 km) seismicity in subduction zones is uncertain. It is typically attributed either to rock embrittlement associated with fluid pressurization, or to thermal runaway instabilities. Here we document glassy pseudotachylyte fault rocks—the products of frictional melting during coseismic faulting—in the Lanzo Mass...
The key role of serpentinites in the global cycles of volatiles, halogens and fluid-mobile elements in oceans and in subduction zones is now ascertained by many studies quantifying their element budgets and the composition of fluids they release during subduction. Geochemical tracers (e.g. B, As, Sb; stable B and radiogenic Sr and Pb isotopes) have...
The chemical and physical processes operating during subduction-zone metamorphism can profoundly influence the cycling of elements on Earth. Deep-Earth carbon (C) cycling and mobility in subduction zones has been of particular recent interest to the scientific community. Here, we present textural and geochemical data (CO, Sr isotopes and bulk and i...
The ophiolitic peridotite and gabbro of Moncuni (Southern Lanzo Massif, Western Alps) retain pre-subduction mantle-to-oceanic, high-temperature (>700C∘) ductile fabrics. These fabrics are overprinted by seismic fracturing and faulting associated with pseudotachylytes. Within the gabbro, the pseudotachylytes preserve dry glass and pristine microlite...
In subduction zones, seismicity and rock rheology are strongly influenced by the presence of fluids. However, the mechanisms governing fluid extraction and transport along the subduction interface are still debated. The meta-peridotite of the Erro-Tobbio Unit (Ligurian Alps) records fluid-rock interaction and associated deformation that occurred at...
Primitive arc magmas are more oxidized and enriched in sulfur-34 (34 S) compared to mid-ocean ridge basalts. These findings have been linked to the addition of slab-derived volatiles, particularly sulfate, to arc magmas. However , the oxidation state of sulfur in slab fluids and the mechanisms of sulfur transfer in the slab remain inconclusive. Jux...
In submarine-hydrothermal systems, fluid-rock interactions play a pivotal role in fostering life on rocky planets. Carbonated-ultramafic rocks (i.e., ophicarbonates) represent an important witness of such environments and their study may provide new insights into hydrothermal processes. Here, we report in-situ trace element concentrations and the f...
Fluids released through the dehydration of serpentinite can be rich in Cl⁻, which enables the significant mobility of Cr in subduction zones. However, the Cr isotope behavior accompanying the mobility of Cr during serpentinite dehydration is still poorly constrained. Here, we report high‐precision Cr isotope data for a unique suite of serpentinites...
Trace element and isotopic compositions of exhumed high-pressure (P) mafic rocks are an important archive to investigate chemical processes in subduction zones. Here we report the B isotope (δ11B) composition of eclogitic mafic rocks enclosed in high-P serpentinite from the Voltri Massif, Ligurian Alps (Italy). Combined with bulk δ18O values, 87Sr/...
Ultramafic and carbonate-rich rocks juxtaposed in an oceanic sedimentary mélange that experienced Alpine subduction (Champorcher, Aosta Valley, Italy) show evidence of metasomatic alteration at their contacts. The reactions that occurred at these contacts afford an assessment of the sources and compositions of fluids associated with the alteration,...
Metasomatic reaction zones between mafic and ultramafic rocks exhumed from subduction zones provide a window into mass-transfer processes at high pressure. However, accurate interpretation of the rock record requires distinguishing high-pressure metasomatic processes from inherited oceanic signatures prior to subduction. We integrated constraints f...
Ultramafic and carbonate-rich rocks juxtaposed in an oceanic sedimentary mélange that experienced Alpine subduction (Champorcher, Aosta Valley, Italy) show evidence of metasomatic alteration at their contacts. The reactions that occurred at these contacts afford an assessment of the sources and compositions of fluids associated with the alteration,...
Here we studied metapelites from the ultrahigh-pressure (UHP) Brossasco-Isasca unit in the Dora-Maira Massif, Western Alps, combining zircon-in-garnet elastic geo-thermobarometry and phase equilibria modelling. We determined the residual strain and pressure of zircon inclusions via micro-Raman spectroscopy and the dedicated softwares available onli...
The origin of intermediate-depth subduction seismicity is a topic of research since long time. While plate unbending is considered as one of the main stress loading mechanisms, the processes responsible for earthquake nucleation are still unclear and depend on the question of whether failure occurs in the wet dehydrating portion of the slab or in t...
Characterizing the pressure and temperature (PT) histories of eclogite–facies rocks is of key importance for unravelling subduction–zone processes at all scales. Accurate PT estimates provide constraints on tectonic and geochemical processes affecting subduction dynamics and help in interpreting the geophysical images of present–day converging plat...
The ultrahigh-pressure (UHP) whiteschists of the Brossasco-Isasca unit (Dora-Maira Massif, Western Alps) provide a natural laboratory in which to compare results from classical pressure (P)–temperature (T) determinations through thermodynamic modelling with the emerging field of elastic thermobarometry. Phase equilibria and chemical composition of...
The Voltri Unit and adjacent Tertiary Piedmont Basin, Western Alps, preserve complementary bedrock and sedimentary archives of Alpine subduction and exhumation. Combined PT modeling and phengite Rb–Sr geochronology of bedrock and clast samples shows that Fe–Ti metagabbros and metasediments preserve a record of protracted high-pressure metamorphism,...
The metamorphic devolatilization of serpentinites during subduction represents the largest potential source of fluids from the subducting slab and influences a range of important processes from subduction zone seismicity to arc magmatism. Obtaining a record of metamorphic dehydration directly from serpentinites, however, is challenging, as serpenti...
This study combines the microstructural and petrological analysis of garnet and its inclusions in quartzite‐hosted garnetite from the ultrahigh‐pressure Lago di Cignana metaophiolite (Western Alps). We present a comprehensive record of metamorphism, compaction, and the state of stress during interaction between oceanic metasediments and infiltratin...
The problem of how dense high-(HP) and ultrahigh-pressure (UHP) metamorphosed oceanic mafic and ultramafic rocks are exhumed from deep within subduction zones is crucial to understanding processes occurring at the interface between the subducting slab and the overlying plate and mantle wedge. In this study, we use the P-T-t evolution of metamorphos...
The structural and chemical properties of zircon inclusions in garnet megablasts from the Dora Maira Massif (Western Alps, Italy) were characterized in detail using charge contrast imaging, Raman spectroscopy, and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The aim of this work is to determine to what extent the degree...
Magnetite–bearing multiphase solid inclusions hosted in metamorphic olivine have been interpreted as final products of the trapping of the aqueous fluid produced by the subduction-zone dehydration of former serpentinites. We provide here a careful analysis performed by micro-focus single–crystal x-ray diffraction of inclusions found in harzburgites...
Understanding the volatile cycles at convergent margins is fundamental to unravel the Earth's evolution from primordial time to present. The assessment of fluid-mobile and incompatible element uptake in serpentinites via interaction with seawater and subduction-zone fluids is central to evaluate the global cycling of the above elements in the Earth...
The Erro Tobbio olivine-antigorite serpentinites and associated dehydration veins represent hydrated oceanic mantle rocks that escaped complete dehydration and recycling into the mantle after subduction to ~ 550-600 °C and 2.0-2.5 GPa. These rocks thus offer valuable insights into the petrological evolution of a slice of hydrated oceanic mantle and...
The Lago Superiore Unit (LSU, Monviso Massif, Italian Western Alps) is a section of fossil oceanic lithosphere equilibrated to eclogite facies conditions (550 °C – 2.8 GPa) during Alpine subduction (45–40 Ma). It is cut by two major shear zones, namely the Intermediate (ISZ) and Lower Shear Zone (LSZ), mostly consisting of serpentinite. The lowermo...
Metamorphic rocks are the records of plate tectonic processes whose reconstruction relies on correct estimates of the pressures and temperatures (P-T) experienced by these rocks through time. Unlike chemical geothermobarometry, elastic geobarometry does not rely on chemical equilibrium between minerals, so it has the potential to provide informatio...
The primary stratigraphic fabric of a chaotic rock unit in the Zermatt Saas ophiolite of the Western Alps was reworked by a polyphase Alpine tectonic deformation. Multiscalar structural criteria demonstrate that this unit was deformed by two ductile subduction-related phases followed by brittle-ductile then brittle deformation. Deformation partitio...
In the Western Alps, the ophiolitic Zermatt–Saas Zone (ZSZ) and the Lago di Cignana Unit (LCU) record oceanic lithosphere subduction to high (540°C, 2·3GPa) and ultra-high pressure (600°C, 3·2GPa), respectively. The top of the Zermatt–Saas Zone in contact with the Lago di Cignana Unit consists of olivine + Ti-clinohumite-bearing serpentinites (the...
Raman spectroscopy provides information on the residual strain state of host-inclusion systems that, coupled with the elastic geobarometry theory, can be used to retrieve the P-T conditions of inclusion entrapment. In situ Raman measurements of zircon and coesite inclusions in garnet from the ultrahigh-pressure Dora Maira Massif show that rounded i...
Elastic geobarometry for host-inclusion systems can provide new constraints to assess the pressure and temperature conditions attained during metamorphism. Current experimental approaches and theory are developed only for crystals immersed in a hydrostatic stress field, whereas inclusions experience deviatoric stress. We have developed a method to...
Ophiolitic serpentinites and secondary peridotites formed by serpentinite dehydration were investigated to improve constraints on the fates of noble gases and halogens during subduction zone metamorphism. The work extends previous studies to encompass F and four stages of serpentinization and serpentinite dehydration including: (i) oceanic serpenti...
Halogens (Cl, F, I, Br) are enriched in surface reservoirs compared to the mantle. The subduction of these reservoirs in the form of sedimentary pore fluids, sediments, altered oceanic crust, and serpentinized mantle lithosphere returns halogens to the mantle and to regions of arc magma genesis. Pore fluids are particularly enriched in I, yet shall...
Fluid-mobile element (FME) systematics in serpentinites are key to unravel the environments of mantle rock hydration, dehydration, and element recycling in subduction zones. Here we compile serpentinite geochemical data and, for the first time, report discriminative FME enrichment trends for mid ocean ridge vs. forearc serpentinisation by applying...
Water within the oceanic lithosphere is returned to Earth’s surface at subduction zones. Observations of metamorphosed veins preserved in exhumed slabs suggest that fluid can escape via channel networks. Yet, it is unclear how such channels form that allow chemically bound water to escape the subducting slab as the high pressures during subduction...
Recent geochemical work shows that subduction-zone serpentinites are repositories for fluid-mobile elements absorbed during interaction with sediment-derived fluids. Unraveling the geochemical fingerprint of these rocks helps to define timing of tectonic accretion of sediments along the subduction interface and the role of serpentinite in element r...
The HP metamorphic serpentinised peridotites of Erro-Tobbio (Italy) offer a unique possibility to study fluid-rock interactions in subducted ultrabasic rocks that reached 550-650°C at 2-2.5 GPa. They contain metamorphic olivine + Ti-clinohumite in both the rock matrix and veins cutting the rock foliation, interpreted to represent partial serpentini...
Much of the long-termcarbon cycle in solid earth occurs in subduction zones, where processes of devolatilization, partial melting of carbonated rocks, and dissolution of carbonate minerals lead to the return of CO2 to the atmosphere via volcanic degassing. We stress that lithologically complex interfaces could contain sites of both C release and C...
Serpentinites release at sub-arc depths volatiles and several fluid-mobile trace elements found in arc magmas. Constraining element uptake in these rocks and defining the trace element composition of fluids released upon serpentinite dehydration can improve our understanding of mass transfer across subduction zones and to volcanic arcs. The eclogit...
We discuss geochemical tracers in serpentinite for assessing the fluid-rock interactions and the element exchange processes experienced by these rocks during subduction. This enables to define the timing of serpentinite accretion to plate interface domains and the evolution of such tectonically active settings. Uptake of As, Sb, Be and reset of B,...
Exposures of low-grade metabasalts and ophicarbonates in the Northern Apennines, and their high- and ultrahigh-pressure metamorphic equivalents in the Western and Ligurian Alps and Tianshan (representing an overall peak P–T range of ~ 0.2–3.0 GPa, 200–610 °C), allow investigation of the effects of prograde metamorphic devolatilization, and other fl...
Exposures of low-grade metabasalts and ophicarbonates in the Northern Apennines, and their high- and ultrahigh-pressure metamorphic equivalents in the Western and Ligurian Alps and Tianshan (representing an overall peak P-T range of ~0.2-3.0 GPa, 200-610°C), allow investigation of the effects of prograde metamorphic devolatilization, and other flui...
Tectonic mixing of slab- and mantle-derived materials at the interface between converging plates highly enhances fluid-mediated mass transfer from the slab to the overlying mantle. Subduction mélanges can provide information about the interaction among different slices accreted at plate interface domains, with implications on the tectonic and geoch...
In active subduction zones, when the converging plates cannot slip freely past each other, "plate coupling" oc-curs. The moving subducting slab and therefore the coupling/decoupling relationship between plates control both short-and long-term deformation of the upper plate. Short-term deformation is dominantly elastic, occurs at human timescales an...
At Cima di Gagnone, garnet peridotite and chlorite harzburgite lenses within pelitic schists and gneisses correspond to eclogite-facies breakdown products of hydrated peridotites and are suitable for studying dehydration of serpentinized mantle. Thermobarometry and pseudosection modelling yield peak temperatures of 750-850 degrees C and pressures <...
Serpentinites form by hydration of ultramafic lithologies in a range of seafloor and shallow subduction zone settings. Serpentinites are recognised as major reservoirs of fluid mobile elements and H2O in subducting oceanic lithosphere, and together with forearc serpentinites formed in the mantle wedge, provide critical information about shallow-lev...
The nitrogen concentrations [N] and isotopic compositions of ultramafic mantle rocks that represent various dehydration stages and metamorphic conditions during the subduction cycle were investigated to assess the role of such rocks in deep-Earth N cycling. The samples analyzed record low-grade serpentinization on the seafloor and/or in the forearc...
We provide 2D thermomechanical numerical models to constrain the subduction process of narrow (~ 600 km wide) oceanic basins resulting in formation and exhumation of serpentinite-bearing highpressure (HP) and ultrahigh-pressure (UHP) complexes presently exposed as dismembered massifs in orogenic belts. We simulated subduction of “heterogeneous” (i....