Heritage Stone 2. The Dora-Maira Unit (Italian Cottian Alps): A Reservoir of Ornamental Stones Since Roman Times

The Dora-Maira Unit is a geological unit cropping out in the inner part of the Cottian Alps and belonging to the Penninic Domain of the Western Alps (northwestern Italy). It consists of a Paleozoic basement and its Mesozoic carbonate cover, metamorphosed under eclogite facies conditions in the Cenozoic. Due to the complexity of the rock associations and the textural-metamorphic transformations, the Dora-Maira Unit has been a source of ornamental stones over the centuries, and still represents a reservoir of material locally employed for historical and contemporary buildings. Several varieties of orthogneiss, quartzite and marble, derived from the Paleozoic basement and Mesozoic cover, are known by different local names (e.g. Luserna Stone, Borgone and Vaie Stone, Perosa Stone, Bargiolina Quartzite, Foresto and Chianocco Marble).These stones were largely employed during the 17th and 18th centuries for some of the most famous and important monuments in Turin (capital of Piedmont region, northwestern Italy), as well as in the countryside, since Roman times. Some of the materials exploited in the Dora-Maira Unit were also exported to foreign countries: Borgone and Vaie Stone were used for the paving of the Louvre Museum, and Perosa Stone was employed for the construction of the monument of Independence in Lagos, Nigeria. Consequently, the Dora-Maira Unit can be designated as a Global Heritage Stone Province.RÉSUMÉL’Unité Dora-Maira est une unité géologique affleurant dans la partie interne des Alpes Cottiennes; elle appartient au Domaine Penninique des Alpes occidentales (Italie du Nord-Ouest). Elle se compose d'une croûte continentale d’âge Paléozoïque supérieur et de sa couverture carbonatique Mésozoïque, métamorphosées en faciès éclogite pendant le Cénozoïque. En raison de la complexité des associations lithologiques et des transformations métamorphiques et structurelles, l’Unité Dora-Maira a été une source de pierres ornementales au cours des siècles, et encore il représente un réservoir de matériau employé localement pour des bâtiments contemporains et historiques. Plusieurs variétés de gneiss, de quartzite et de marbre, provenant du socle paléozoïque et de la couverture mésozoïque et connues sous différents noms locaux (par exemple Pierre de Luserna, Pierre de Borgone et Vaie, Pierre de Perosa, Bargiolina, marbres de Foresto et Chianocco), étaient largement utilisées pour certains monuments les plus célèbres et importants à Turin (capitale de la région Piémont), au cours des 17ème et 18ème siècles, et dans les alentours de la ville depuis l'époque romaine. Certains des matériaux exploités dans l'Unité Dora-Maira ont été également exportés aux pays étrangers: la Pierre de Borgone et Vaie a été utilisée pour le pavage du Musée du Louvre, et la Pierre de Perosa a été employé en Afrique, à Lagos, au Nigéria, pour la construction du monument de l'indépendance. Par conséquent, l'Unité Dora-Maira peut être indiquée comme une Pierre Province du patrimoine mondial

Alpine tectonic evolution and thermal water circulations of the Argentera Massif (South-Western Alps)

Three groups of thermal springs with temperatures close to 70 °c discharge both in the core (at bagni di Vinadio and terme di Valdieri) and on the external margin (at Berthemont-Les-Bains) of the Argentera Massif. Detailed structural field analysis carried out on the hydrothermal sites allows us to delineate both a model of Alpine tectonic evolution of the Argentera Massif and the patterns of hydrothermal circulation that were active during its final exhumation. the observed fault rock assemblages provide information relative to deformation that occurred in viscous, frictional-to-viscous and frictional crustal regimes. During the Early Miocene, the bersezio Fault Zone and the Fremamorta shear Zone, two main mylonitic shear zones, mainly accommodated regional transpression and provided pathways for fluid flow promoting mineral reactions in greenschist facies. During the Late Miocene-Early Pliocene, frictional-to-viscous deformation affected the massif, which underwent predominant transpression in the internal sectors and extension on the external margin. During the Plio-Pleistocene, deformation in frictional condition accompanied the final exhumation of the massif in a transpressive regime and resulted in the development of the NW-SE striking cataclastic zones. The hydraulic properties of these structures mainly influence the patterns of the active thermal circulations and the localization of the recharge and discharge zones. At Berthemont these faults represent conduits, whereas at Vinadio and Valdieri they form complex systems of conduits and barriers. In these two latter sites, the cataclastic faults compose flower structures that constrain laterally the thermal fluid flows while intensely fractured granites sited at depth constitute a highly-transmissive geothermal reservoir. Less permeable migmatitic gneisses overlaying the granites prevent a massive infiltration of the cold fluids at depth. This context favours within the high-ermeability fractures granites the development of buoyancy-driven flows which combined with topographically-driven flows, provided the conditions for the pflow of the high-temperature waters. © Birkhäuser Verlag, Basel, 2009

Geology of the Fontane talc mineralization (Germanasca valley, Italian Western Alps)

The 1:5000 scale Geological Map of the Fontane talc mineralization (FTM) aims to give new information about the origin and geological structure of an important talc mineralization occurring in the axial sector of the Italian Western Alps. The FTM is hosted within a pre-Carboniferous polymetamorphic complex which was deformed and metamorphosed during both Variscan and Alpine orogenesis, and is part of the Dora-Maira continental crust. Field mapping and underground investigations highlight that the talc bodies (i) never crop out but occur at depth along a well-defined lithostratigraphic association between micaschist, marble and gneiss and (ii) were deformed during different Alpine-related deformation phases (i.e. D1, D2 and D3 syn-metamorphic phases and post-metamorphic extensional faulting). The here defined lithostratigraphic and structural characterization of talc bodies, is an input for further research into the geodynamic context of where talc forms and for new mineral exploration outside the mapped area

UNDERSTANDING LATE-STAGE EXHUMATION USING AN INTEGRATED MULTIDISCIPLINARY APPROACH: A CASE STUDY IN THE INNER COTTIAN ALPS (NW ITALY)

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Pre-Orogenic Tectonostratigraphic Evolution of the European Distal Margin-Alpine Tethys Transition Zone in High-Pressure Units of the Southwestern Alps

Geological mapping, stratigraphic observations, and U/Pb dating allow reconstructing the pre-orogenic setting of the transition zone between the distal European passive margin and the Alpine Tethys in the southwestern Alps. Although convergent tectonics overprinted the syn-rift Jurassic tectonic features, our data document an articulated Jurassic physiography. From the distal European passive margin oceanward, we distinguished: the Dronero Unit (the southernmost Dora Maira massif), represents a continental margin composite basement wherein monometamorphic metasediments are interlayered with Late Permian (253.8 ± 2.7 Ma) metavolcanic rocks; the Sampeyre Unit, represents a structural high consisting of Lower Triassic Verrucano-facies siliciclastic metasediments unconformably sealed by Cretaceous calcschist bearing Globotruncana sp.; the Maira Unit, corresponds to a Middle Triassic platform succession detached from the Sampeyre Unit; the Grana Unit, corresponds to a Late Triassic–Late Jurassic platform to basin succession; the Queyras Schistes Lustrès Complex, represents the ocean basin succession. Tectonic slices of Cambrian (513.9 ± 2.7 Ma) metadiorite hosted in the Valmala Shear Zone, separating the Dronero Unit from the underlying (U)HP units of the Dora Maira massif, suggests a potential pre-Alpine activation of the shear zone

Seismotectonic investigations in the inner Cottian Alps (Italian Western Alps): An integrated approach

This work integrates the results of recent geological–structural studies with new seismological data for the inner Cottian Alps to investigate the connection between faults and seismicity. The major post-metamorphic tectonic feature of this sector is represented by a N–S structure, named Lis–Trana Deformation Zone (LTZ). Since the Late Oligocene, this structure accommodated right-lateral (Late Oligocene–Early Miocene) and subsequently normal (post-Early Miocene) displacements. In the Pleistocene, the activity of the LTZ seems to have caused the development of lacustrine basins inside the valleys that drain this sector of Western Alps. The present-day seismicity joins the northern part of the LTZ and, southwards, other minor sub-parallel structures. In transversal cross-section hypocentres highlight steep surfaces. Focal mechanisms calculated along this structure show both extensional and strike–slip solutions, mostly with one roughly N–S striking nodal plane. Both sub-horizontal (with NE–SW to ENE–WSW trend) and steeply dipping P axes with N–S to NW–SE sub-horizontal T axes are observed. Even if clear evidence of Quaternary tectonic activity in the area is missing, on the basis of the available seismological and geological data we propose that in the inner Northern Cottian Alps the present-day seismic activity may be connected to the LTZ, interpreted as minor sub-parallel fault strand of the Canavese Line. The kinematics of this structure is consistent with the focal mechanisms calculated in this area. Structural and seismological data indicate that LTZ is active under a bulk dextral–transtensive regime since the late Oligocene in the inner Cottian Alps, in agreement with the data published for the adjacent domain of the chain.Published1-163.3. Geodinamica e struttura dell'interno della TerraJCR Journalrestricte