Roberto Compagnoni

• CEO at University of Turin

A petrographic study of “Verde Prato” (trade name of an ophiolitic serpentinised peridotite quarried in Tuscany) revealed, next to a relict Cr-spinel, another opaque ore mineral apparently containing ca.17 wt% SiO2. In order to unveil the origin of this anomalous composition, detailed SEM-EDS, μ-Raman spectroscopy and X-ray μ-diffraction investigat...

Metamorphic fluids, faults, and shear zones are carriers of carbon from the deep Earth to shallower reservoirs. Some of these fluids are reduced and transport energy sources, like H2 and light hydrocarbons. Mechanisms and pathways capable of transporting these deep energy sources towards shallower reservoirs remain unidentified. Here we present geo...

An eclogite-facies orthogneiss and host paragneiss from a quarry near Tavagnasco in the Lower Aosta Valley were studied in order to refine the protolith, provenance and metamorphic ages of the Eclogitic Micaschist Complex of the Sesia Zone. The orthogneiss contains jadeite with quartz + phengite + K-feldspar ± garnet + rutile + zircon, whereas the...

The ultramafic body of Monte Avic (Aosta Valley, Western Alps, Italy) consists of antigorite serpentinite and Ti-clinohumite metadunite. They host late metamorphic veins, up to a couple of centimeters thick, compact, and homogeneous, with a “porcelain” appearance. Vein colors range from yellowish to light greenish, light yellowish fading to white,...

Metamorphic fluids and deformation zones are fundamental carriers of carbon from the deep Earth to shallower reservoirs. It is well established that water weakens rocks and contributes to trigger seismicity. Conversely, the potential effects of carbon-rich aqueous fluids on deep-seated rocks remain little studied. Some of these fluids may be reduce...

This paper sheds light on syn-exhumation, pervasive cataclastic processes occurred on competent serpentinites of a metaophiolitic sub-unit of the Voltri Massif. The reported data highlight the importance of the compositional and structural heterogeneities within the ophiolite-bearing exhumation channels, since the observed pervasive cataclastic pro...

The Canavese Zone, in the Southern Alps, preserves evidence of multi-stage lithospheric thinning leading to the Jurassic opening of the Western Tethys. Crustal thinning and exhumation of subcontinental mantle at the basin floor are best observed at the southern end of the Canavese Zone, between the villages of Levone and Rivara. A small ultramafic...

The greenstone industry of Valgrana/Tetto Chiappello was studied with an archaeo-typological and mineral/petrographic approach (functional study, XRPD, polarized light microscopy and SEM-EDS), to infer the provenance of the raw materials and the role of this site in the general greenstone circulation during Neolithic. Most artifacts (mainly cutting...

The oldest documented use of the “Verde Prato” (synonymous are: Nero di Prato, Serpentinite) dates back to XI century for the façade of the Miniato Basilica at Florence; in the XI-XIII centuries the Verde Prato was widely used for columns, ashlars, decorations and church cladding in the area of Prato, Florence, Pistoia and Empoli (Tab.I), where con...

Subduction plate margins have an intrinsically poor preservation potential for pre-subduction settings because most rocks sink and disappear into Earth’s mantle. However, a preserved pre-subduction setting has been reported in the Lower Penninic Units (Valaisan Basin) of the Italian Western Alps (Beltrando et al., 2012). Here, we review two main as...

The Monte Fico lizardite crystals have an internal skeletal spongy microstructure, formed by two micrometric domains having different optical reliefs. This intracrystalline microstructure parallels the previously reported intercrystalline arrangement, consisting of lizardite prisms within a chrysotile plus polygonal serpentine matrix. In the high-w...

The serpentine minerals lizardite, polyhedral serpentine, chrysotile, antigorite and 15‐sector and 30‐sector polygonal serpentine have been studied by micro‐Raman spectroscopy, using selected samples, that had been previously characterized. The appropriate crystal orientations were determined by optical microscopy of petrographic sections. Oriented...

Naturally-Occurring Asbestos (NOA) may constitute a severe health risk when metamorphic rocks are excavated for large infrastructure projects. For public acceptance, a reliable assessment of the content of NOA is necessary for the design of the construction site, workers' safety, and spoil management. Direct measurements of NOA content can be made...

This contribution describes a geodatabase structure designed to manage a large amount of geo-environmental data for the "Gronda di Genova" highway by-pass tunnels in Liguria region (Italy). In particular, an innovative dataset structure founded on an explicit conceptual model was designed to represent the distribution of petrofacies containing Natu...

Asbestos may constitute a severe health risk when meta-ophiolites are excavated for large infrastructural projects. For public acceptance, a reliable estimation of the content of Naturally Occurring Asbestos (NOA) is necessary for the design of construction sites, workers' safety and spoil management. In the framework of a research project supporti...

Supplementary material

The polished stone industry of Chiomonte (Piedmont region, northwestern Italy), dating back to the middle to late Neolithic, has been studied with a multi-analytical approach, including mineralogical, petrographic and morpho-typological issues, with the aim of providing information about the sources of the raw materials and determining the function...

The presence of naturally occurring asbestos (NOA) in many areas worldwide requires an enhanced geological risk evaluation to ensure workplace safety from asbestos during large construction projects. Due to the complexity of the geological risk definition, health and safety regulations for working with asbestos-bearing materials are often not enfor...

For a reliable evaluation of the geo-environmental risk due to naturally occurring asbestos (NOA) during rock excavation of large infrastructure projects, a proper procedure is needed. First, it is necessary to provide a detailed geological model tailored to the NOA-related issues that should drive the rock sampling procedures in order to obtain a...

Realization of large geo-engineering projects in rocks containing naturally occurring asbestos (NOA) must address several crucial geo-environmental issues, including the design of the construction site, the enforcement of health protection measures and the environmentally responsible spoil management. This leads to a compelling need to develop effe...

Appendix A. Supplementary data

Scanning electron microscopy with energy dispersive spectrometry (SEM-EDS) is the only affordable analytical technique that can discriminate both morphology and elemental composition of inorganic fibers. SEM-EDS is indeed required to quantify asbestos in confounding natural matrixes (e.g. ophiolites), but is also time-consuming, operator dependent,...

A large crystal of trigonal phengite (Phe-3T; K0.96Na0.02Ba0.01)(Al1.35Mg0.40Fe²⁺0.11Fe³⁺0.13Ti0.02)Σ=2.02[Si3.44Al0.56]O10(OH)2), sampled from a phengite+quartz metamorphic vein in the eclogites-bearing rocks of Sulu UHP metamorphic terrane, exhibits unusual thin lamellae of ferrian-aluminian trigonal/monoclinic phlogopite polytypes (Phl-3T: (K0.7...

A multidisciplinary approach to the study of orogenic belts allows to develop a better knowledge of their geodynamic evolution and may suggest new models, especially for (U)HP rocks. In the axial sector of the Western Alps, several tectonic units in mid-Susa Valley preserve the different stages of their geodynamic evolution, from the early stages o...

The Piemonte Geological Map is the graphical layout of a GIS Map and Geodatabase designed to represent the Alps-Apennines orogenic system from latest Cretaceous to Quaternary. The map was mostly compiled using available data (starting from historical maps of the beginning of the twentieth century to the most recent ones), which were in some cases r...

Magnesiobeltrandoite-2N3S, ideally Mg6Al20Fe23+O38(OH)2, is a new member of the högbomite supergroup of minerals. It occurs in magnesian chloritites of a metamorphosed layered mafic complex in the Etirol-Levaz continental slice, middle Valtournenche, Aosta Valley, Italy. Magnesiobeltrandoite-2N3S grows in a fine-grained chlorite matrix associated a...

Alteration of ultramafic rocks plays a major role in the production of hydrocarbons and organic compounds via abiotic processes on Earth and beyond and contributes to the redistribution of C between solid and fluid reservoirs over geological cycles. Abiotic methanogenesis in ultramafic rocks is well documented at shallow conditions, whereas natural...

Supplementary Figures, Supplementary Tables and Supplementary References.

Magnesiobeltrandoite-2N3S, ideally Mg6Al20Fe³⁺2 O38(OH)2, is a new member of the högbomite supergroup of minerals. It occurs in magnesian chloritites of a metamorphosed layered mafic complex in the Etirol-Levaz continental slice, middle Valtournenche, Aosta Valley, Italy. Magnesiobeltrandoite-2N3S grows in a fine-grained chlorite matrix associated...

The polished stone axes deposit of Ceglie Messapica is a corpus of not ordinary artefacts. Thanks to its uniqueness, it allows to investigate the raw material circulation in Southern Italy and to examine how a precise idea bound to skilled production of large polished blades had spread among the Neolithic-Eneolithic élites, in order to show their s...

IMA No. 2016-073 Magnesiobeltrandoite-2N3S (Mg6Al2)(Al18Fe3+2)O38(OH)2 Marmore stream, middle Valtournenche, Valle d’Aosta, Italy (45°49′36″N, 7°34′51″E) Fernando Cámara*, Roberto Cossio, Daniele Regis, Marco E. Ciriotti and Roberto Compagnoni *E-mail: fernando.camaraartigas@unimi.it Högbomite supergroup Trigonal: P3m1; structure determined a = 5.7...

The Arch of Augustus in Susa (north-western Italy) was built in 9-8 bc by King Cottius, to celebrate the treaty between the Romans and the Gauls. It is made of white marble, which was considered for a long time to be locally extracted, but no archaeometric studies have been performed up to now. Therefore, a multi-analytical study based on petrograp...

High-pressure and ultra-high pressure (HP-UHP) blueschist- and eclogite-facies metabasaltic and metasedimentary rocks occur in four different tectonic units near Lago di Cignana, western Alps. We have determined K-Ar ages for white micas (matrix phengite and paragonite) from the Lago di Cignana UHP unit (LCU; 39–41 Ma); the lower and upper units of...

High-pressure (HP) meta-ophiolites-usually termed 'greenstones' by archaeologists-were used in the Neolithic to produce polished stone implements all over Western Europe. Their accurate petrographic characterization may help to infer the provenance of the raw materials, thus contributing to reconstruct the migratory routes of our ancestors. The lit...

Both natural and artificial materials used in the several construction phases of the Cluny priory in Castelletto Cervo (Biella, NW Italy) have been studied and classified petrographically. The cobbles have been determined on the base of the only macroscopic examination, being fresh samples of relatively coarse-grained igneous or metamorphic rocks....

This short manuscript presents a detailed investigation into the metamorphic evolution of a unique corundum-bearing chloritite from the layered metagabbro body within the Etirol-Levaz continental slice in Valtournenche, Aosta, Italy. This sample represents the first occurrence of corundum and högbomite-bearing mafic rocks in the Western Italian Alp...

High and ultra-high pressure metamorphic rocks have a crucial role in the construction of geodynamic models concerned with convergent plate margins. They offer the possibility of constructing P-T-t trajectories, and thus constrain the evolution of orogenic belts. In this work, new structural and metamorphic data were collected in the Susa Valley, w...

In many urban and natural areas, the presence of naturally occurring asbestos (NOA) requires a geological risk evaluation to enforce safety and exposure monitoring during the achievement of surface and subsurface infrastructures. A set up of proper procedures must provide: (i) a detailed geological model of the possible presence of the asbestos, (i...

Dear Editors, we read with surprise and concern the paper published by Ilgren et al [1]. The explicit purpose of this paper is to exclude the role of chrysotile in the mesothelioma epidemics among workers of the former San Vittore mine (Amiantifera di Balangero) and inhabitants in the Balangero area. In search of other causes, gross mistakes have b...

Metamorphism of the Askore Amphibolite, metabasltic and metasedimentary medium-grade horblende-bearing schists at the northernmost portion of tje Ladakh Terrane and of the Shyok Suture Zone, mainly a low-grade volcano-sedimentary series, has been studied in the area between the Chogo Lungma glacier and the Indus river halfway between Skardu and Ron...

Microdiamonds in garnet of graphite-free ultrahigh pressure metamorphic (UHPM) rocks from Lago di Cignana (western Alps, Italy) represent the first occurrence of diamond in a low-temperature subduction complex of oceanic origin (T = ∼600°C; P ⩾ 3.2 GPa). The presence of diamonds in fluid inclusions provides evidence for carbon transport and precipi...

A great number of prehistoric stone implements from Western Europe are made of high-pressure (HP) metamorphic lithotypes, such as Na-pyroxenites and fine-grained eclogites. These rocks represent minor “accessory” lithologies that occur as either small primary outcrops or secondary clastic deposits derived from erosion of the former. Due to their sc...

In order to promote geosite conservation in the project entitled ‘PROactive management of GEOlogical heritage in the PIEMONTE Region’, we propose a comprehensive study involving the Monviso Massif (MM) geothematic area, one of the most outstanding symbols of the Alps and particularly of the Cottian Alps. Specifically, at the MM, the inventory of a...

The overall metamorphic reaction in an impure calcite marble from the ultra-high pressure (UHP) zone at Changpu, eastern Dabie Shan, China, is partitioned into local reaction domains defined by isolated grains of omphacite, garnet, epidote, quartz and ilmenite within the calcite matrix. These reaction domains witness different stages of the metamor...

The Valaisan Domain, in the Petit St. Bernard Pass area (Punta Rossa unit, Western Alps), consists of largely serpentinized sub-continental mantle juxtaposed with Paleozoic basement, meta-pillow lavas and Mesozoic to Tertiary meta-sediments. The complex lithostratigraphy was largely acquired during rift-related extensional tectonics, when mantle pe...

Alpine Corsica consists of a stack of variably metamorphosed units of continental and Tethys-derived rocks. It represents an excellent example of high-pressure (HP) orogenic belt, such as the Western Alps, exposed over a small and accessible area. Compared to the Western Alps, the geology of Alpine Corsica is poorly unraveled. During the 1970s–80s,...

Two magnesite-bearing impure dolomitic marbles from the Dabie–Sulu ultrahigh-pressure (UHP) region have been investigated to clarify if they had actually attained P–T conditions outside the dolomite stability field, limited by the reaction dolomite = aragonite + magnesite, and to test their potential for recording (U)HP conditions. In both cases, t...

In the southern Dora-Maira Massif, Western Alps, slivers of continental crust with similar lithologies, but recrystallized during the Alpine orogeny at different peak-P conditions, are exposed. They include the Brossasco-Isasca Unit (BIU) where coesite was first discovered in continental crust. A new 1:20,000-scale geologic map and related cross-se...

Transition from blueschist to eclogite facies is considered as a major step of dehydration during subduction of oceanic crust. In cold subduction zones, this critical transitional field is characterized by the stability of lawsonite, which represents the major H2O carrier in HP basaltic rocks. Lawsonite-bearing eclogites are commonly associated wit...

A block is described, which is exposed in the antigorite serpentinite of Vallone Bule, belonging to the Basal Serpentinite Unit of the Monviso massif (Piemonte Zone of calcschists with meta-ophiolites). The block consists of a quartz-jadeite rock core and a jadeitite rim, very similar to the rocks used by prehistoric men to make stone axeheads. In...

In subduction zones, the so-called subduction channel is believed to represent the locus where the primary exhumation of deeply subducted material occurs. It is also considered as a major zone of deformation and tectonic shuffling [1, 2]. The resulting intense deformation that is commonly observed in exhumed subduction terranes is generally conside...

Subduction zones modulate the global carbon cycle. Carbon is transported into the mantle by the subducting slab and returned to the surface by degassing at arc volcanoes above the subduction zone(1,2). However, the mechanisms for the transfer of carbon from the subducting slab and sediments into the overlying mantle wedge are poorly understood. Dec...

Here we discuss the fate of subducted carbonates and its implications for recycling of crustal carbon. Thermodynamic models predict little decarbonation along most subduction geotherms, and the mechanisms by which carbon is transferred from the subducting slab to the overlying mantle remain poorly constrained. Diamond-bearing fluid inclusions in ga...

The new highway ring of the city of Genoa, the so-called “Gronda di Ponente”, aims to reduce road traffic along the existing A10 route, now absorbed by the urban fabric; the plan includes a double-tube main tunnel, by-pass and access tunnels for more than 50 km of underground works, to be excavated by means of both TBM and D&B technique. In the pro...

An unusual occurrence of palygorskite was found near Montestrutto, lower Val d'Aosta (Italy), within an eclogite-facies leucogneiss of the Sesia-Lanzo zone. Under the optical microscope the mineral appears as a felt of fibres hundreds of μm long and a few μm thick. SEM observation proved each filament to be a bundle of smaller but remarkably long f...

In Alpine Corsica (France), deeply subducted metabasalts are well preserved as lawsonite-bearing eclogite (Law-Ecl), occurrence of which is restricted to ∼10 localities worldwide. The Corsican Law-Ecl, consisting of omphacite + lawsonite + garnet + phengite + titanite, occurs as both single undeformed metabasaltic pillows surrounded by lawsonite bl...

In the Schistes Lustrés of Alpine Corsica (France) serpentinized mantle rocks are associated with continental basement and meta-volcanic/-sedimentary cover rocks. The relationships among these different lithologies are especially well exposed in the Monte San Petrone unit, where Alpine metamorphism reached lawsonite-eclogite conditions. The contact...

CorseAlp 2011 was held in April 2011. A link to the website is here: CorseAlp 2011. The CorseAlp field trips were designed to introduce the participants to the general features of the geology of Alpine Corsica and to recent specific discoveries. Field trip 1 focused on the geology of the Ocean-Continent Transition preserved in the Monte San Petrone...

A petrological and thermobarometric study of the Lago Teleccio hornfelses was undertaken to reconstruct the polymetamorphic evolution and constrain the P–T conditions of Permian contact metamorphism. The Lago Teleccio metasedimentary rocks record a Variscan regional metamorphism characterized by amphibolite facies mineral assemblages including quar...

We report the first occurrence of microdiamonds in garnetites from the ophiolitic ultra-high pressure (UHP) Lago di Cignana unit, Italian Western Alps, derived from Mn-rich nodules. Microdiamonds, indentified by laser Raman spectroscopy and optical and electron microscopy, display all of the typical features of subduction diamonds formed at UHP con...

We report on Alpine metamorphic and fluid inclusion evolution of a polyphase rodingite occurrence within the Bellecombe antigorite-serpentinite, exposed in the Piemonte zone of Aosta Valley, NW Italy. Fine-grained rodingitic rocks, derived from a protolith of basaltic dike(s), are cross-cut by a network of at least six vein generations, consisting...

The main felsic lithologies experiencing ultrahigh-pressure metamorphism (UHPM) are described, with a focus on rock association, nature, and composition of the peak minerals, as well as nature of the protolith. Felsic rocks usually preserve poor evidence of UHPM, being pervasively deformed and retrogressed during exhumation. Locally, however, unstr...

The Pressure–Temperature–time–deformation evolution of the high- to ultra-high-pressure units of the Western Alps has been progressively refined in the last 40 years, leading to several paradigm shifts in the understanding of orogenesis. This set of information, combined with Cretaceous–Tertiary plate kinematic reconstructions and Mesozoic palaeoge...

The type of lithosphere reaching subduction zones has profound implications for the evolution of orogenic belts and for mass balance calculations in the subduction factory. Numerical and conceptual models of subduction generally distinguish between only two types of lithosphere: (1) oceanic and (2) continental, with the latter consisting of subcont...

The age of high-pressure metamorphism is crucial to identify a suitable tectonic model for the vast Variscan orogeny. Banded HP granulites from the Gesso-Stura Terrain in the Argentera Massif, Italy, have been recently described (Ferrando et al., 2008) relicts of high-pressure metamorphism in the western part of the Variscan orogen. Bulk rock chemi...

This study provides new 40Ar/39Ar geochronological constraints on the age of the Alpine tectonics in the Aspromonte Massif (southern part of the Calabrian–Peloritan belt). This massif exposes the upper units of the Calabride Complex which originated from the European continental margin. The Calabride Complex was incorporated in the Alpine orogenic...

The "External Crystalline Massifs" of the Western Alps (Mont Blanc, Aiguilles Rouges, Grandes Rousses, Belledonne, Pelvoux, and Argentera) consist of a polymetamorphic Variscan basement, which was only marginally reworked during the Alpine tectonometamorphic cycle. These massifs experienced an early subduction event at peak metamorphic conditions o...

The type of lithosphere reaching subduction zones has profound implications for the evolution of orogenic belts and for mass balance calculations in the subduction factory. Numerical and conceptual models of subduction generally distinguish between only two types of lithosphere: (1) oceanic and (2) continental, with the latter consisting of subcont...

Composition and provenance of slab-derived hydrous fluids and melts represent a key parameter in understanding the geochemical variations of subduction-related magmas. Chemical and physical characteristics of the slab components may be strongly reliant upon both the thermal structure of the mantle wedge, and the nature of the subducted lithosphere....

The ultrahigh-pressure pyrope whiteschists from the Brossasco-Isasca Unit of the Southern Dora-Maira Massif represent metasomatic rocks originated at the expense of post-Variscan granitoids by the influx of fluids along shear zones. In this study, geochemical, petrological and fluid-inclusion data, correlated with different generations of pyrope-ri...

We present a petrological and geochronological study of “silvery micaschists” that crop out in the northern side of the Gran Paradiso Massif, Western Alps, with the aim of constraining P–T conditions and age of the Alpine high-pressure metamorphism. The studied “silvery micaschists”, which are the products of metasomatic alteration of granitoids al...

To evaluate the biodurability of balangeroite, present as contaminant of chrysotile asbestos in the Balangero mine, in order to have indication whether it might have been a confounding factor in the association of the mesothelioma cases reported among mine workers and employees. The modifications taking place following incubation of the fibres in s...

In the Western Alps, the ocean-derived Lago di Cignana Unit of the Piemonte Zone has experienced ultrahigh-pressure metamorphism. We have studied the minerals of two eclogite samples from this unit using transmission electron microscopy (TEM) in order to characterise their microstructures. These microstructures are the result of deformation, phase...

The island of Sifnos (Cyclades, Greece) is famous for its spectacular blueschist-facies rocks and eclogites. Their very well preserved high-pressure assemblages are characterized by the occurrence of Fe+3-rich minerals such as aegirine-rich pyroxene, riebeckite-rich amphibole, magnetite and deerite. Therefore, the common model system NCFMASH (Na2O–...

The Lago di Cignana ultra-high-pressure unit (LCU), which consists of coesite–eclogite facies metabasics and metasediments, preserves the most deeply subducted oceanic rocks worldwide. New constraints on the prograde and early retrograde evolution of this ultra-high pressure unit and adjoining units provide important insights into the evolution of...

The mechanisms underlying asbestos toxicity mainly rely on experiments performed on "laboratory" fibers, but little data is available on naturally occurring asbestos (NOA). Human exposure to NOA is subject to their ecopersistence and the modulation of their potential toxicity following weathering. The effect of weathering on three fibrous minerals...

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We report SEM-EDS, WDS, micro-Raman, IR-synchrotron-radiation imaging, and LA-ICP-MS data on minerals and multiphase solid inclusions (MSI) in equilibrium at UHP peak in Dora-Maira whiteschists. These rocks consist of pyrope-rich garnet, quartz/coesite, phengite, kyanite, talc, chlorite, and minor Mg-rich minerals. Three generations of pyrope occur...

We propose to investigate the diamonds from the Kokchetav Massif, northern Kazakhstan, which is the best example of diamond-eclogite facies metamorphism, using cathodoluminescence (CL) techniques. CL spectra measurements of diamonds from garnet-pyroxene-quartz rocks and dolomitic marbles, made at 80 K, revealed peaks at 2.156, 2.463, and 3.188 eV a...

At the Frisson Lakes (FL), a small layered mafic sequence surrounded by migmatitic orthogneisses is exposed as a tectonic window of the crystalline basement of the Gesso-Stura Terrain (GST) of the Argentera Massif (Western Alps, Italy) within its Meso-Cenozoic sedimentary cover. The mafic sequence is characterised by Pl-rich and Pl-poor layers of H...