Marco Gattiglio

Breccia-hosted manganese-rich minerals of Alpi Apuane, Italy: A marine, redox-generated deposit

Mn-rich beds occur within the “Brecce di Seravezza” Formation (BSFm) intercalated between Norian metadolostone-Megalodontic marble and Hettangian marble in the Alpi Apuane, (Italy). The BSFm is a rockfall talus deposit that accumulates at the base of the footwall scarp of normal faults bordering extensional marine coastal basins. The type sequence of metabreccia ends with a bed of chloritoid schist interpreted as the metamorphic equivalent of lateritic soils. The four main types of Mn mineral assemblages are: (1) braunite, piemontite, and rare hausmannite; (2) piemontite, braunite, hollandite and minor rhodochrosite and kutnahorite; (3) braunite, hollandite and rare piemontite. The other minerals are: quartz, calcite, muscovite, phlogopite, baryte and minor hematite, rutile and apatite. During the Alpine orogeny pressures of 4–6 kb and temperatures of 350 °–380 °C were attained; Mn assemblages with hematite and phlogopite indicate ƒO2 > 10−8 for T= 350 °C and ƒO2 ≥ 10−6 when braunite appears. On the Mn-rich rocks Ti, Fe, Nb, Sn, Ta, Hf, Th, Ga, Rb, Pr, K, Na, Nd were identified as detrital in origin and are positively correlated with Al. U is positively correlated with Co, Pb, Bi, Mo. The rare earth element patterns normalized to seawater show a negative slope towards the heavy rare earth elements, with positive Ce anomalies in some samples, positive Ce and Eu anomalies in other samples and negative Ce and positive Eu anomalies in a third group. The Eu concentrations are nearly constant and the Eu anomalies reflect differences in the concentration of other rare earth elements; for Ce, a positive correlation with Al2O3 + SiO2 indicate that a detrital signature prevails on that produced by duration of seawater exposure. But a significant good correlation of La, Tm, Lu with Mg could indicate, at least for these elements a seawater signature. Only in some samples, Ba, Eu, Sr show anomalously high concentrations, likely of hydrothermal origin. However, generally in all the chemical variation diagrams the BSFm samples fall outside the field of hydrothermal and hydrogenous deposits as defined in the literature for other Mn deposits. In addition, metabasites and metavolcaniclastic beds are absent from the BSFm sequence and BSFm coastal basins were for the most part separated from the open ocean and related streams, that must be excluded as possible Mn-sources. Owing to the arid climate of Late Triassic the runoff was negligible and the groundwater, oxidizing and alkaline, were unable to mobilize Mn. The BSFm basins are then the most suitable depositional environment for Mn. The water column was stagnant and stratified. Only where bottom of the basin was deeper than the oxic-anoxic boundary, reducing marine bottom waters percolated within the fractured basement and leached Mn from disseminated minerals of metamorphic rocks and, then, rising along fault and fractures, supplied Mn to the bottom waters. Afterwards, when tectonic uplift and sealevel drop brought the bottom into the oxic field, Mn precipitated and formed the Mn-rich matrix of the BSFm deposits.

Detailed geological mapping in mountain areas using an unmanned aerial vehicle: application to the Rodoretto Valley, NW Italian Alps

ABSTRACT We present a methodology to use a UAV (unmanned aerial vehicle) to perform photogrammetric surveys and detailed geological mapping in mountain areas. This work is specially related to the presented case study with the aim to realize geomorphological maps from UAVs, since they can house different types of sensors and acquire data more rapidly and cheaply than traditional geological surveys directly obtained with field observations. This work explains how UAVs can obtain digital terrain models, orthophotos and 3D models in order to create slope and aspect maps for geological purposes. By integrating data from UAVs with geological surveys made on the field, geological maps can be produced where many of the geological elements are presented. This paper presents the integration of geomatics and geological techniques. Starting from UAV slope map and orthophotos, a new geological map was created in a faster and more detailed way compared to traditional geological survey on the ground. The application of this method regards a sector of the Western Alps (NW Italy), formed by glaciers and deep-seated gravitational slope deformations.

Geochemistry and origin of chloritoid schist from the Alpi Apuane, Italy: evidence of a prevailing lateritic signature.

Chloritoid schist layers frequently occur as the uppermost part of the Rhaetian Brecce di Seravezza Formation, interpreted as rockfall talus metabreccias intercalated between Norian and Liassic marbles, in the Alpi Apuane Tuscany, Italy. The chloritoid schist is characterised by mm-sized chloritoid porphyroblasts (20–50 % modal range) and a matrix made up of chlorite, muscovite, pyrophyllite, chloritoid, hematite, calcite, quartz and epidote. Most chloritoid porphyroblasts show cores with abundant hematite inclusions. Many pieces of duricrust, pisoid and composite pebbles come from older lateritic bauxite deposits of supposed Kasimovian to Sakmarian age. Their uneven to well rounded shapes indicate variable duration of transport and multistage reworking. In comparison with many bauxite and metabauxites, Apuan chloritoid schist shows: great enrichment in SiO 2 , K 2 O, Na 2 O, a slight increase in CaO, MgO, remarkable depletion in Al 2 O 3 and Fe 2 O 3 , a slight decrease in TiO 2 and P 2 O 5 , strong depletion in Cu, Pb, Zn, Bi, and As, unexpected Ni, Co and Ba enrichments; slight to strong depletion for Ga, Cr, Nb, Zr, and V reflecting variable dilution of primary bauxite detritus. The REE spider diagram shows enrichment factors of 2–3 for LREE, of 1–2 for HREE. Strong enrichment to strong depletion in Sm, Eu, Gd, and Tb is correlated with maximum and minimum contents of duricrust fragments respectively. Four detrital components were distinguished. Two of them represent about 90–95 % of the whole protolith: 1. Fe 2 O 3tot -Al 2 O 3 -SiO 2 -rich lateritic bauxite detritus; 2. illite-rich desert soil particles with high K 2 O, SiO 2 , Al 2 O 3 contents. The calculated relative proportions are: component 1): 61 %, component 2): 39 %. Minor detrital components are given by: 1) Ba-rich mineralised rock fragments, a witness to Late Triassic hydrothermal circuits; 2) detritus supplied by Na, Ca, Mg-rich salts abundant in hot desert soils. The very low TiO 2 and very high SiO 2 contents of the calculated lateritic bauxite component strongly suggest a granite to rhyolite protolith for the primary bauxite deposit, the ancestor of the Apuan lateritic bauxite component.

Tectonostratigraphy of the northern Monviso Meta-ophiolite Complex (Western Alps)

The Monviso Meta-Ophiolite Complex is a remnant of the Piedmont-Ligurian oceanic lithosphere stacked in the Western Alps, andconsisting of dismembered HP meta-ophiolite sequences. In thiswork, focused on the northern sector of the Complex, we differen -tiate six tectonic units which structural, petrographic and stratigraphiccharacteristics are described in detail and discussed in thelight of a comparison with the overall geology of the MonvisoMeta-Ophiolite Complex. The structural evolution has been referredto i) an early syn-eclogitic deformation phase (D1), ii) a main deformationphase (D2) occurred in the blueschist- to greenschist-faciestransition and characterized by the development of a regional foliation(S2) that is parallel to the tectonic contacts and to the axialplane of map-scale W-verging folds, and iii) a late-metamorphicdeformation phase (D3) characterized by westward extensionaltectonic. The northern Monviso Meta-Ophiolite Complex is characterizedby a poor preservation of HP paragenesis and a widespreadoverprint of the blueschist- to greenschist-facies metamorphism,but the occurrence of garnet-, omphacite-, talc- and lawsoniteassemblagein a Fe-Ti metagabbro indicates P-T eclogitic conditions(2.5-2.7 GPa for 550-570 �C) very similar to those calculated in thesouthern sector of the Complex. The stratigraphic characteristics ofthe meta-ophiolite sequences point out that, differently from thesouthern sector of the Complex where basalt-poor and basalt-richoceanic units have been distinguished, in the northern MonvisoMeta-Ophiolite Complex the different types of metasedimentsmay be the key to restore the oceanic tectonostratigraphy, markedby gabbro and mantle peridotite exposition on a puzzle-like oceanfloor where basalt effusion and different sedimentation processestook place.

Geological map of the middle Orco Valley, Western Italian Alps

Abstract Please click here to download the map associated with this article. Detailed mapping of the middle Orco Valley in the Western Italian Alps allowed for the reconstruction of the lithostratigraphy and the structural evolution of different tectonic units along a geological section from the Gran Paradiso Massif to the Gneiss Minuti Complex of the Sesia-Lanzo Zone. The studied nappes can be grouped into a Lower Tectonic Element which underwent eclogite facies metamorphism and an Upper Tectonic Element pervasively equilibrated under greenschist facies conditions and lacking evidences of high pressure metamorphism. The mapping of Quaternary deposits, geomorphological features and brittle structural elements provided evidence for the occurrence of a deep-seated gravitational slope deformation on the left side of the middle Orco Valley.

Tectonically-related fluid circulation in the San Casciano dei Bagni-Sarteano area (M. Cetona ridge-Southern Tuscany): a coupled structural and geochemical investigation

The aim of this investigation is to examine the relationship between springs and structural setting in the Mt. Cetona Ridge. This area represents an important regional morpho-tectonic feature oriented NNW-SSE, separated from the geothermal area of Monte Amiata to the West by the Radicofani Neogene Basin, and bounded to the East by the Valdichiana Neogene-Quaternary Basin. This Ridge is constituted by the Tuscan Nappe and the overthrusted S. Fiora Unit. New detailed field mapping and a structural study allowed recognition of a polyphase structural setting defined by four folding phases followed by three extensional and transtensional phases. Coupled to the structural investigation, 13 spring water samples were collected in the area in May and in August 2005. Groundwater ranges from cold, low mineralized calcium-bicarbonate to warm, highly mineralised, calcium sulphate. Results are in general agreement with previous studies indicating the recharge area in the Cetona upland and a circulation in a highly fractured, quasi-continuous reservoir constituted by the Mesozoic limestone and the underlying Burano anhydrite formation. Geochemical modelling indicates that the high variability in the hydrochemical and isotopic composition cannot be explained by a simple binary mixing between two ground-water types, but rather reveals a geochemical evolution involving anhydrite and dolomite dissolution, and calcite precipitation. Outflows are closely related to the structural setting of the area and hydrochemistry allows discrimination of different fluids associated with specific hydrogeological circuits. The interpretation of the structural setting for Mt. Cetona Ridge was obtained by fieldwork studies integrating geochemical data of both thermal and cold springs. Results of this investigation allow us to propose a new tectonic evolution and fluid circulation model for this area.

Role of Late Jurassic intra-oceanic structural inheritance in the Alpine tectonic evolution of the Monviso meta-ophiolite Complex (Western Alps)

The eclogite-facies Monviso meta-ophiolite Complex (MO) in the Western Alps represents a well preserved fragment of oceanic lithosphere and related Upper Jurassic–Lower Cretaceous sedimentary covers. This metaophiolite sequence records the evolution of an oceanic core complex formed by mantle exhumation along an intra-oceanic detachment fault (the Baracun Shear Zone), related to the opening of the LigurianPiedmont oceanic basin (Alpine Tethys). On the basis of a detailed geological mapping, and structural, stratigraphic and petrological observations, we propose a new interpretation for the tectono-stratigraphic architecture of the MO, and discuss the role played by structural inheritance in its formation. We document that subductionand exhumation-related Alpine tectonics were strongly influenced by the inherited Jurassic intra-oceanic tectono-sedimentary physiography. The latter, although strongly deformed during a major Alpine stage of non-cylindrical W-verging folding and faulting along exhumation-related Alpine shear zones (i.e., the Granero-Casteldelfino and Villanova-Armoine shear zones), was not completely dismembered in different tectonic units or subduction-related mélanges as suggested in previous interpretations. The presentday architecture of the MO results from nappe-scale folding with a significant component of shearing, and strain partitioning of the Alpine deformation, which were controlled by the inherited occurrence of (i) lateral and vertical variations of facies and thickness of sediments, (ii) intra-oceanic fault-rock assemblage, which acted as weak horizons in concentrating deformation, and (iii) remnants of a volcanic ridge, which consists of massive metabasalt. Thus, the recognition of pre-collisional, intra-oceanic, tectono-stratigraphic inheritance represents an important step in reconstructing the tectonic evolution of meta-ophiolite units in orogenic belts.

Distribution, Discharge, Geological and Physical–Chemical Features of the Springs in the Turin Province (Piedmont, NW Italy)

Numerous exploited springs (1571) have been investigated in the Turin Province. They have been mapped with a GIS on a new, specially drafted, geolithological map and statistically examined with regard to areal distribution, discharge, use and lithological composition of their catchment basin. One spring every 4 km2 occurs in this area. In detail, the spring density is greater in the mountains (1 spring every nearly 3 km2) than in the plains and in the hills (1 spring every 10–53 km2). These springs are well-distributed in the different altitude ranges, with two peaks at 800–1,100 m and at 140–300 m. They are mostly used for drinking water supply (65 %), irrigation (23.5 %), sanitary use (6 %) and, subordinately (5.5 %), industries, fish farms, production of electric energy and unknown use. The 54.7 % of the springs has discharge lower or equal to 1 l/s, while only the 2.7 % (43 springs) has discharge greater than 10 l/s. A 81 l/day drinking water supply each inhabitant is estimated per capita. The spring areal distribution into the different geolithological units and their discharge values (linked to the aquifer typology) are synthetized. A sample of 28 analyzed springs has bicarbonate to sulfate alkaline-earth facies. Their electric conductivity (100–400 μS/cm) is due to content of bicarbonates (mean value of 100 mg/l) and sulfates (mean value of 15 mg/l). In a single basin (Dora Riparia) the Total Hardness exceeds 25 French Degrees.

ERT geophysical surveys contributing to the reconstruction of the geological landscape in high mountain prehistorical archaeological sites (Plan di Modzon, Aosta Valley, Italy)

One of the few examples of high mountain prehistorical archaeological sites in northern Italy has been discovered within the so called Plan di Modzon area, at 2300 m a.s.l., in the Aosta Valley (Western Alps). This area shows interesting geological features and morphological evidence which have been recently linked to a wide Deep-Seated Gravitational Slope Deformation (DSGSD). A probable filled lake and the presence of buried landforms have been also hypno tized on the basis of geological observations, resulting in the need for new devoted surveys to confirm these hypotheses. A better and comprehensive understanding of the geological evolution of the area is indeed necessary to allow a precise reconstruction of the environments in which man has inhabited these territories. Combined Electric Resistivity Tomographies (ERT) and geological surveys have been therefore used to better define the occurrence and nature of morphological evidence along the western slope of the filled lake, in which one of the archaeological sites has been discovered and excavated. The outcomes of the integration of the two surveys is a more refined definition of the geological forms, in respect to the one previously assumed on the basis of surface surveys only. Indeed, ERT revealed buried zones with low resistivity associable to the presence of sliding surfaces and also showed the geometry and thickness of the sediments within the filled lake. Geological surveys also evidenced a DSGSD evolution in the area constrained to Lateglacial, because of the lack of particularly evident gravitative forms, i.e. remodeled by glacial abrasion.

Use of water resources in mountain. The case study of the Montellina Spring.

Lucchi, Renata G. ... et. al.-- 87° Congresso della Societa Geologica Italiana e 90° Congresso della Societa Italiana di Mineralogia e Petrologia, The Future of the Italian Geosciences - The Italian Geosciences of the Future, 10-12 September 2014, Milan, Italy.-- 1 pageThe Montellina Spring (370 m a.s.l.) represents an example of groundwater resource in mountain region. It is a significant source of drinking water located in the right side of the Dora Baltea Valley (Northwestern Italy), SW of Quincinetto town. This spring shows a morphological location along a ridge, 400 m from the Renanchio Torrent in the lower sector of the slope. The spring was investigated using various methodologies as geological survey, supported by photo interpretation, structural reconstruction, NaCl and fluorescent tracer tests, discharge measurements. This multidisciplinary approach, necessary due to the complex geological setting, is required for the importance of the Montellina Spring. It is interesting in the hydrogeological context of Western Alps for its high discharge, relatively constant over time (average 150 l/s), and for its location outside a fluvial incision and suspended about 40 m above the Dora Baltea valley floor (Lasagna et al. 2013). According to the geological setting, the hydrogeological reconstruction of the area suggests that the large amount of groundwater in the basin is essentially favoured by a highly fractured bedrock, covered by wide and thick bodies of glacial and gravitational sediments. The emergence of the water along the slope, in the Montellina Spring, is essentially due to a change of permeability between the deep bedrock and the shallow bedrock and/or surficial sediments. The deep bedrock, showing closed fractures and/or fractures filled by glacial deposits, is slightly permeable. The shallow bedrock, strongly loosened as result of gravitational phenomena, and the local gravitational sediments are, on the contrary, highly permeable. The concentration of water at the spring is due to several reasons. a) The spring is immediately downward a detachment niche, dipping towards the spring, that essentially drains the water connected to the change of permeability in the bedrock. b) It is along an important fracture, that carries a part of the losses of the Renanchio Torrent. c) Finally, it is favored by the visible and buried morphology. Although it is located along a ridge, the spring occurs in a small depression between a moraine and a landslide body. It also can be favored by the likely concave trend of buried base of the landslide. At last, tracer tests of the Renanchio Torrent water with fluorescent tracer are performed, with a continuous monitoring in the Montellina Spring. The surveys permit to verify and quantify the spring and torrent hydrogeological relationship, suggesting that only a small fraction of stream losses feeds the spring.