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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 paragneiss hosts garnet + jadeite + phengite ± glaucophane + epidote + rutile + quartz. Phase diagram modeling of two representative samples yields minimum equilibration conditions of 550 ± 50 ∘C and 18 ± 2 kbar. Cathodoluminescence images of zircon from the orthogneiss show oscillatory-zoned cores that are embayed and overgrown by complex, oscillatory-zoned rims. Four concordant secondary ion mass spectrometry analyses from the cores give a weighted mean 206Pb / 238U age of 457 ± 5 Ma. The cores have Th/U = 0.1 and negative Eu anomalies indicative of an igneous protolith, which we interpret to have crystallized in the Ordovician at 780 ∘C, based on Ti-in-zircon measurements. Zircon rims yield a range of 206Pb / 238U dates from 74 to 86 Ma, and four concordant analyses define a weighted mean 206Pb / 238U age of 78 ± 2 Ma. The rims are interpreted to have grown in the eclogite facies based on their lower Th/U (0.01), less negative Eu anomalies and steeper heavy rare earth element (HREE) patterns at ∘C. The paragneiss yielded a detrital zircon population with major peaks at 575–600, 655 and 765 Ma; minor older components; and a maximum depositional age of approximately 570 Ma. The prominent Neoproterozoic zircon population and Ediacaran depositional age suggest derivation from the Gondwana margin. The metamorphic zircon is consistent with the oldest eclogite-facies event in the Sesia Zone; it does not show evidence of multiple periods of rim growth or any pre-Alpine (e.g., Variscan) metamorphism.

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, or rare orange. The veins consist of 15-sector PS-15 polygonal serpentine, with chemical composition Mg2.85 Fe0.08 Si2.05 O7.05 [OH]3.95. Recognition of this unusual phase is supported by diagnostic satellite reflections in the X-ray powder diffraction pattern (e.g., at dobs of 2.502, 2.336, 2.151, and 1.966 Å) TEM images (showing 15-sector polygonal fibers, mostly 200 nm in diameter and a few µm in length, forming a randomly oriented felt) and a µ-Raman wavenumber, matching previous data. This different evidence affords the successful distinction of PS-15 and PS-30, alternatively using TEM images, X-ray powder diffraction, or the low- and high-wavenumber µ-Raman spectra. At Monte Avic, the vein emplacement was accompanied by significant fluid pressure, as suggested by deformation and dismembering of the host rock, with PS-15 grown within isotropic stress microenvironments characterized by fluid-filled voids. Random growth of the mass-fiber polygonal serpentine was favored by low-strain conditions. PS-15 veins formed at the end of the long polyphase Alpine orogenic evolution, with hydrous fluids possibly deriving from serpentinite dehydration in the depth.

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-wavenumber region, the larger and more abundant domains (that represent approximately 87 % of the total field view) produce μ-Raman spectra characterized by two major peaks at 3686 and 3705 cm−1. The smaller, less abundant domains present a wide band confined between these wavenumbers. These features are interpreted as lizardite and chrysotile, respectively. Raman results are confirmed by TEM, which emphasizes the presence of well-recognizable polygonal serpentine too. Tight crystallographic control exists between lizardite and this first serpentine generation. A second serpentine generation occurs perpendicularly to the first one. The lizardite crystals grew up with a skeletal habit, whereas chrysotile fibres and polygonal serpentine filled the voids, growing epitactically on the lizardite crystals, with fast crystal growth in a fluid-rich environment.

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 of this particular settlement in the prehistoric Western Alps. Most of the lithic tools are made of sensu stricto greenstones (i.e. “Na pyroxene rocks” and “Na pyroxene and garnet rocks”), though a large number of serpentinite tools (25 %) also exist. The combined application of X-ray powder diffraction (XRPD), polarising microscopy and Scanning Electron Microscopy coupled with Energy Dispersive Spectrometry (SEM-EDS) led to the detection of specific mineral and chemical “markers”, pointing to the Chiomonte tools likely having come from the Monviso area. However, other closer supply sources, e.g. small meta-ophiolite units in the Orsiera–Rocciavré mountain range or in the lower Susa valley, cannot be ruled out. The presence, on the many retrieved roughouts and broken tools, of raw, yet unpolished surfaces that are ascribable to pebbles and cobbles from alluvial or glacial deposits, suggests that these rocks had been picked up from local “secondary” sources. The abundance of roughouts and broken tools identifies Chiomonte as a second-order manufacturing site, although it is still unclear whether such an activity was restricted to serving local needs or if it contributed to the circulation of greenstone implements on a wider scale.