Lawsonite eclogites are rare rocks and have been described from only a few localities in the world. Lawsonite-bearing assemblages are highly unstable and physico-chemical processes linked to exhumation may destroy them; only aggregates interpreted as pseudomorphs after lawsonite could be often recognized. In this paper, we present a detailed structural and petrological study of an area in the northwestern sector of the metaophiolitic high-pressure Voltri Massif (Ligurian Western Alps, Italy). The study area is characterized by a lawsonite-bearing eclogitic metagabbro associated with carbonated serpentinites and glaucophanic metasediments. The metagabbro body reached eclogitic metamorphic peak conditions atT= 465–477°C andP= 20.9–24.4 kbar, with H₂O continuously supplied to the system. H₂O under-saturated conditions, with the occurrence of both lawsonite and epidote, characterized the exhumation path. Both the low temperature recorded by the body and the occurrence of variously carbonated serpentinites led us to interpret this area as a portion of the top of the subducted slab, coupled with a ‘cool’ mantle wedge, where both aqueous fluids and carbonate-rich fluids were present. The occurrence of rocks belonging to different paleogeographic domains (e.g. continent versus ocean) and the multiple deformations recorded by the metagabbro suggest that this area was nearby the slab–mantle interface. This sector was thus affected by a shear regime that acted in a low-viscosity serpentinite channel, bringing these high-pressure rocks back to the surface.

The aim of this work is to present a new georeferenced geological map of an area in the Ligurian Western Alps (Lavagnina Lakes area) that includes both a unique geodiversity and great biodiversity, a peculiar geological heritage, and cultural features. The study area is located in the northern part of the Capanne di Marcarolo Regional Natural Park, occurring in the southern Piedmont Region (Alessandria, NW Italy) and close to the suburbs of Genoa. This area has been studied by multi-disciplinary scientific researchers who, so far, have focused their attention on the occurrence of alkaline springs and investigation of different endemic floral species. Moreover, in the past, the Lavagnina Lakes area has been exploited due to the presence of gold mineralization, and several mining records are still visible. We performed detailed geological mapping at a 1:10,000 scale, and collected data that were later integrated into a digital GIS map. The database associated with the map contains information that may be interesting from different points of view: (i) scientific research; (ii) outreach and dissemination activities; and (iii) geotourism (i.e., trail networks and panoramic viewpoints). The area represents a section of the Jurassic Piedmont Ligurian oceanic lithosphere, showing several geologic processes on different scales, such as the serpentinization process and intense and widespread carbonation of ultramafic rocks; the area is, moreover, characterized by fault systems showing paleoseismic structures. Beyond scientific research activities (i.e., geology, geoarchaeology, and mining archaeology), the area can also be promoted for geotourism, outreach and dissemination activities, field trips for schools, and gold panning activities. Hence, our new digital map and our 3D model could be a useful tool to illustrate the main characteristics of the area, leading a non-expert public to explore different geological features in a relatively “small” area. In this way, our map could help to improve geotourism, be used as a tool for educational activities, and, finally, could also help the Capanne di Marcarolo Regional Natural Park to be recognized as a geopark.

The Bisciarelle fault is a brittle thrust crosscutting lherzolite of the Voltri Massif (Italy) and is similar to the historical gold veins of the area. This is a 16-m-thick fault showing a large damage zone and a 4-m-wide hydrothermal alteration halo. Its fault rocks interacted with a hydrothermal fluid and host peculiar Au-bearing zones made of concentric and circular dolomite aggregates, which we call spherulites, and chalcedony. To constrain spherulite genesis, we quantify fluid-fault interactions at Bisciarelle combining field and microtextural data, mass transfer calculations, and a multi-technique analytical dataset including element imaging by laser ablation-inductively coupled plasma-time-of-flight mass spectrometry. We show that faulting was coupled with significant transfer of H₂O, CO₂, Ca, Sb, and W from the fault fluid to the protolith, and variable transfers of SiO₂ and some trace elements from the protolith to the fluid. This process deposited Au within the spherulites, caused serpentinization and carbonation of the protolith, and weakened the fault localizing subsequent shearing events and providing components for the growth of spherulites and the other fault rocks.We interpret Bisciarelle as a permeable epizonal orogenic vein, which formed fast as a result of dilation and top-to-NE shearing. This fault developed via cycles of fluid pressure build-up, opening, fluid effervescence, and mineral precipitation from a H₂O-CO₂ hydrothermal fluid. The fluid transported and deposited a suite of metals including Au and interacted with the protolith. A similar mechanism of faulting and reactive fluid flow could have generated the other Au deposits of the area.

This new map at 1:25,000 scale covers an area in the Western Alps (Italy), where the HP metamorphic basement is covered by a (predominantly clastic) late- and post-orogenic upper Eocene-lower Miocene cover. This provides unequivocal evidence that exhumation of the metamorphic units was accomplished by the lower Oligocene. The basement is made up of tectonic units with different metamorphic peaks that coupled during the exhumation path. Both basement and cover are affected by long-wavelength, asymmetric folds and thrust faults with top-to-E-NE vergence; this deformation phase has long been interpreted as linked to the rotation of the Corsica-Sardinia block and contemporary opening of the Liguro-Balearic basin and beginning of the Apennine orogeny. We particularly investigated some of these structures that crop out in the mapped area to give further constraints on their distribution, type and kinematics and to frame them in a larger picture of left-hand strike-slip tectonics.