Papers by giacomo oggiano
HTLP metamorphism and fluid‐fluxed melting during multistage anatexis of continental crust (N Sardinia, Italy)
Journal of Metamorphic Geology
The Variscan high‐grade metamorphic basement of northern Sardinia and southern Corsica record low... more The Variscan high‐grade metamorphic basement of northern Sardinia and southern Corsica record lower Carboniferous anatexis related to post‐collisional decompression of the orogen. Migmatites exposed in the Punta Bianca locality (Italy) consist of quartz + biotite + plagioclase + K‐feldspar orthogneisses, garnet and cordierite‐bearing diatexite and metatexites, derived from metasediments. Field evidence, petrographic observations, ELA‐ICP‐MS zircon and monazite dating and pseudosection modelling suggest that anatexis was apparently episodic involving two main stages of partial melting. Using pseudosection modelling, we infer that the first stage of partial melting is in the upper amphibolite facies (~0.45 GPa at ~740°C). Cordierite overgrowths replacing sillimanite, combined with the composition of plagioclase and K‐feldspar, suggest decompression followed cooling below the solidus at low pressures of ~0.3 GPa. The age of the first anatectic event is not precisely constrained because...
Geology of late-Variscan Sàrrabus pluton (south-eastern Sardinia, Italy)
Journal of Maps, 2021
ABSTRACT This paper deals with the geological mapping of the late-Variscan Sàrrabus pluton, (sout... more ABSTRACT This paper deals with the geological mapping of the late-Variscan Sàrrabus pluton, (south-eastern Sardinia), a shallow multiple and composite igneous complex dominated by several generations of granodiorites, metaluminous and peraluminous granites and repeated pulses of mantle-derived mafic magmas. The map has been compiled based on geological surveys at 1:10,000 and 1:5,000 scales, assisted by in situ gamma-ray spectrometry and detailed petrographic investigations. Granite-related ore deposits have been also reported. The emplacement age of the pluton can be constrained by U/Pb dating on zircons of Cala Regina granodiorite, yielding an age of 286 ± 9 Ma. The resulting scenario documents a bimodal magmatism controlled by an EW trending shear zone, followed by the shallower emplacement of several pulses of independent granite magmas.
Polyphasic deformation of the Mesozoic and tertiary succession in the Supramonte (Eastern Sardinia)
Pre-hecynian Magmatic Activity in the Nappe Zone (External and Internal) of Sardinia:evidences of two Wthin-Plate Basaltic Cycles
The Jibal Qutman deposit: first notes on a new gold discovery in the Arabian Shield (Kingdom of Saudi Arabia)
Chemical variability of peri-gondwanian Ordovician igneous activity: geodynamic significance and regional comparisons (Sardinia and Ligurian Alps)
Cassiterite Vein Deposits Related to Late VariscanIlmenite-series in SW Sardinia (Italy): Insights for a NewTin Province
Into the depth of the Arburèse vein system: arsenide-sulfide evolution in the Ni-Co ores
Review of Scientific Instruments, 2020
The Einstein Telescope (ET) is a proposed next-generation, underground gravitational-wave detecto... more The Einstein Telescope (ET) is a proposed next-generation, underground gravitational-wave detector to be based in Europe. It will provide about an order of magnitude sensitivity increase with respect to the currently operating detectors and, also extend the observation band targeting frequencies as low as 3 Hz. One of the first decisions that needs to be made is about the future ET site following an in-depth site characterization. Site evaluation and selection is a complicated process, which takes into account science, financial, political, and socio-economic criteria. In this paper, we provide an overview of the site-selection criteria for ET, provide a formalism to evaluate the direct impact of environmental noise on ET sensitivity, and outline the necessary elements of a site-characterization campaign.
Environmental Earth Sciences, 2020
Groundwater quality can be compromised by its interaction with deep thermal waters. In northern S... more Groundwater quality can be compromised by its interaction with deep thermal waters. In northern Sardinia, two different deep thermal-water-flow systems have recently been recognized on the basis of thermal and isotopic features. One system (GW) is hosted in deep, mainly granitic, fractured reservoirs with water temperatures of 30-45 °C and Cl-Na hydrofacies. These waters have high fluoride contents owing to their alkalinity and water-rock interactions during long residence times in the reservoirs. Their bulk chemistry indicates chemistry by concentrating elements of environmental concern through adsorption, such as first-row transition metals and some chalcophile elements. The other system (AW) involves volcano-sedimentary rocks with water temperatures of 20-30 °C. These waters have neutral pH and are categorized as bicarbonate-alkaline and alkalineearth hydrofacies. Their relatively high contents of chalcophile elements are consistent with their high dissolved CO 2 contents; major elements are in equilibrium with kaolinite, which has a low cationic exchange capacity. In both of these flow systems, B speciation depends on pH. Furthermore, Mn and Fe occur as Mn 2+ and Fe 2+ species, respectively, depending on Eh-pH conditions. High Mn and Fe concentrations are derived from the reduction of Fe oxyhydroxides, releasing adsorbed Mn 2+. The direct reduction of Mn 4+ phases of Tertiary volcanic rocks also produces high Mn 2+ concentrations. Fe oxyhydroxide reduction, at near-neutral pH, can also promote mobilization of As as HAsO 4 2− or, with increasing pH, as H 2 AsO 4 − species. Trace-element analyses and speciation modeling indicate marked differences between GW and AW thermal-water systems, but neither contains metal concentrations at sufficient levels to cause health concerns via water consumption.
The post-collisional late Variscan ferroan granites of southern Sardinia (Italy): Inferences for inhomogeneity of lower crust
Lithos, 2017
Abstract The post-collisional late Variscan magmatism of Sardinia-Corsica batholith attained a pe... more Abstract The post-collisional late Variscan magmatism of Sardinia-Corsica batholith attained a peak at about 290 Ma. In southern Sardinia, in the frontal part of the Variscan orogenic wedge, this magmatism is represented by three suites of granitoids, here defined as GS1, GS2 and GS3. GS1, GS2 and GS3 are slightly peraluminous and F-bearing granitoids; GS1 and GS3 granites show in addition a ferroan character, whereas GS2 rocks range from magnesian to ferroan, from granodiorites to leucogranites. From magnetic susceptibility data, GS1 and GS2 belong to the ilmenite series, whereas GS3 is a slightly oxidized rock-suite plotting on the ilmenite/magnetite series boundary. Each rock-suite shows distinctive characters, in terms of petrography, petrochemistry, rock associations, as well as metallogenic signature of the related fluids. The distinction among rock-suite types is made on the basis of both mafic and characteristic accessory minerals. Siderophyllitic dark mica as the only mafic phase, and accessory xenotime (Y) characterize the GS1 rocks; GS2 mineral associations include biotite ± hornblende + allanite + magnetite; GS3 rocks show an association of hastingsite + annite + allanite + magnetite. Chemical variations in the studied samples suggest different magmatic evolution of independent magmas. Pb, Sr and Nd isotopic data constrain the origin of magmas to lower crustal sources. Chemical composition of rocks and dark micas meet those of liquids experimentally obtained by low degrees of partial melting of different meta-igneous deep crustal sources, felsic for GS1 rock-types and more mafic for GS3 rock-types. GS1 intrusions show granophile-type (Sn-W-Mo) metallogenic signatures, very low magnetic susceptibility, and Nd model ages (referred to the Depleted Mantle - T DM ) of 2.3 Ga, coherent with a possible derivation from an old (early Proterozoic-Neoarchean), reduced and weathered basement, tectonically buried under Variscan covers. A definite deep crustal inhomogeneity is mirrored by GS3 granites, whose compositional and isotopic features indicate a younger (Nd model age: 1.6 Ga) tonalitic amphibolite source. Overall, the peculiarities of the studied granitoids suggest further compositional differences in the deep crust between southern and northern portion of the Sardinia-Corsica Variscan transect. Late Variscan lithospheric delamination appears as the most reliable mechanism that may have determined the high thermal regime that triggered partial melting of the crust. The close field association, at 290 Ma, of tholeiitic dike swarms and ferroan granitoids, supports this inference.
Journal of Maps, 2018
This paper illustrates the geological and structural map (scale 1:10,000) of the Castellaccio Plu... more This paper illustrates the geological and structural map (scale 1:10,000) of the Castellaccio Pluton (Asinara island-Italy), a peraluminous granodioritic intrusion of Variscan age that belongs to the Corsica-Sardinia Batholith. This small pluton, about 15 km 2 , emplaced within Paleozoic amphibolite-facies rocks during the post-collisional exhumation of the chain. The map shows the fine details of the magmatic structure of the pluton. Field-structural survey, coupled with remote sensing and major-elements geochemical mapping, allowed to recognize the occurrence of five magmatic units and the magmatic flow trajectories within the pluton. These outcomes provide useful insights into the architecture of the magmatic system. The results presented improve substantially the cartographic database of the Variscan crust of Sardinia and, finally, may serve as a robust background supporting further studies on the emplacement mechanism, or targeted to more specific petrologic studies.
Ore Geology Reviews, 2017
Bauxite is a residual rock, consisting mainly of a mixture of aluminium hydroxides, whose industr... more Bauxite is a residual rock, consisting mainly of a mixture of aluminium hydroxides, whose industrial significance is primarily due to its profitably exploitable alumina contents. In the last decades, bauxite, mainly karst bauxite, has been also considered as possible resource of a great number of economically interesting elements including some critical metals such as rare earth elements, Sc, Co, Ni, and Nb. In this study, we present results of univariate and multivariate (R-mode factor analysis) statistics performed on a large data set including chemical composition of the principal Cretaceous karst bauxites from central and southern Italy with the twofold aim to evaluate the inter-elemental relationship among major oxides and critical metals, and describe factors affecting their distribution. Univariate statistics reveal that some critical metals Co, Ni, and LREE, have a significant number of outliers. The Co-Ni relationship associated to the outliers dataset suggests that Co is likely hosted in Ni-rich phases whereas Ce accumulation in authigenic minerals, carbonate-fluoride and phosphate, is at the origin of LREE outliers. Multivariate R-mode statistics, applied to the outliers-devoid database, instead demonstrate that in absence of specific mineralization events, the distribution of most critical metals is controlled by Al-, Fe-, and Ti-oxi-hydroxides and, to a lesser extent, by detrital phases. Among the critical metals, Cr and Y are the exceptions. Their geochemical behaviour seems to be influenced primarily by their own chemical features that are responsible for the mobility of Cr during bauxitization and for the decoupling of Y from the REEs.
Journal of Maps, 2015
Over the last 25 years the Italian national geological mapping program of the Italian Geological ... more Over the last 25 years the Italian national geological mapping program of the Italian Geological Survey (CARG Project, italian: Progetto Carta Geologica) at 1:50,000 scale has led to significant improvements in the geological knowledge for the Island of Sardinia (Italy). As a result, about one half of the island now is covered by new geological maps with 1:10,000-1:25,000 accuracy and geological maps at the 1:50,000 scale whose explanatory notes are available electronically. At the beginning of the CARG Project a geological map for Sardinia Island at 1:200,000 scale was published [Carmignani, L. (1996). Carta Geologica della Sardegna (1:200.000). Servizio Geologico Nazionale, Regione Autonoma della Sardegna], summarizing all the geological information available at that time, and a book with explanatory notes for the map was later published [Carmignani, L
Journal of Maps, 2015
This paper presents the geological, structural and metallogenic map of the Arbus Pluton, a late V... more This paper presents the geological, structural and metallogenic map of the Arbus Pluton, a late Variscan composite intrusion belonging to the Corsica-Sardinia Batholith. The pluton is surrounded and crosscut by a wide variety of vein ore deposits. The Arbus Pluton was emplaced at shallow crustal levels at the end of the Variscan Orogeny, along an E-W trending shear zone located in the low-grade external nappe pile of the Sardinian basement. The architecture of the pluton is roughly concentric with a core of cordierite-bearing leucogranites and an outer shell composed of pyroxene-bearing and hornblende granodiorites. New U/Pb dating on zircons of granodiorite yields an emplacement age of 303.7 ± 1.1 which improves previous Rb/Sr and Ar/Ar dating. The map has been compiled on the basis of new geological/structural surveys and petrographical studies coupled with in situ gamma ray spectrometry. All the data-sets have been processed using a geographical information system.
Geochemistry and Rb/Sr ages of Syn-Tectonic peraluminous granites of Western Gallura (Northern Sardinia, Italy): Constraints on their genesis
Periodico di Mineralogia
Antarctic Geological 1: 250.000 Map Series-Sequence Hills Quadrangle
Tectonophysics, 2015
The Corsica-Sardinia Batholith formed in the late Carboniferous-Permian along the northern Gondwa... more The Corsica-Sardinia Batholith formed in the late Carboniferous-Permian along the northern Gondwana margin. One or more of the following processes may have raised the Variscan geotherm enhancing melting of the crust and uppermost mantle, such as: i) break-off and detachment of the Rheic oceanic slab, ii) mantle delamination due to gravitational re-equilibration of thickened crust, iii) shear heating, iv) advection of mantle-derived melts, and v) concentration of heat-producing elements. In this paper, we present a simple one-dimensional thermal model to explain the origin of the batholith in a geodynamic setting consistent with intraplate shearing between Gondwana and Cadomian-Avalonian blocks. Input parameters, and boundary and initial conditions of the model crust are derived from a careful re-examination of large petrological, geochronological, and structural datasets. All parameters are varied within a range of geologically realistic values to reproduce thermal histories related to different tectonic processes, and the reliability of models is quantitatively evaluated by comparing the simulated geotherms with a large dataset of pressure-temperature-time (P-T-t) constraints. The best fit to P-T-t constraints is obtained for: i) break-off in the Late Devonian-Early Carboniferous, ii) decreasing exhumation rates from 340 to 280 Ma, and iii) transpression at high average strain rates, mostly coeval with the peak of high-T-low-P metamorphism.
Palaeogeography, Palaeoclimatology, Palaeoecology, 2014
Red beds deposits of Permian-Triassic basins of Sardinia (western Italy), where a wide segment of... more Red beds deposits of Permian-Triassic basins of Sardinia (western Italy), where a wide segment of the Variscan orogen is exposed, were studied. The basins were selected according to their position within the structural zones of Variscan orogen, i.e. from the external to the inner sectors of the chain. Detailed mineralogical, petrographical, and chemical analyses were performed on shale and calcrete layers laying along the sedimentary sequences, to examine their compositional features and stratigraphic variation. In this regard, enrichment factors (F (e)) for major and trace elements (relative to the PAAS composition) were calculated and discussed. Several geochemical proxies were also calculated and used to assess the palaeoclimate conditions during the red beds deposition. The weathering indices (CIA and CIW) accounted for more humid conditions in the basins of the axial zone relative to the basins those of the foreland, which instead were characterised by an arid climate. However, the presence of carbonates, albeit discontinuous, and the values of calcification, salinity, and hydrolysis indices suggest that, in the axial zone, dry and hot periods also occurred. Compositional data of the sedimentary records were correlated to the Sardinia geological setting and significant information were obtained on the palaeoenvironment characterizing the southwestern Mesoeurope during Permian and Triassic. Al 2 O 3-TiO 2-Zr ternary plot and Zr/Sc vs. Th/Sc diagram show that both sorting and sedimentary recycling affected the studied basins. Precisely, our data lead us to suppose that a wide regional subsidence caused both the recycling of uplifted Variscan rocks and the diagenetic K-metasomatism of Permian sediments revealed by the A-CN-K diagram. Finally, a supply from upper continental source has been suggested by the provenance proxies (such as (Gd/Yb) N and Eu/Eu*) and the LaTh -Sc plot that also reflect the paucity of mafic rocks in feeding areas.
Uploads
Papers by giacomo oggiano