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The Arbus igneous complex (SW Sardinia, Italy) represents a good example of a short time lived post-collisional composite pluton emplaced at shallow crustal level in the external zone of the Variscan chain. The pluton almost consists of granodiorite and leucogranite rock-suites emplaced at 304 ± 1 Ma within a main NW trending thrust separating the metamorphic wedge from the fold and thrust belt foreland. The pluton emplaced into a dilatational step over connecting two NW–SE dextral shear zones which belongs to a regional network of post-collisional strike-slip structures marking the transition from collision to post-collisional extension. The microstructure observed for quartz and K-feldspar confirms the lack of significant post-emplacement deformation, indicating only limited high-temperature sub-solidus recrystallization. Anisotropy of magnetic susceptivity data and field-structural analysis have been carried out to reconstruct the geometry of the pluton and the trajectories of magmatic flow in relation to regional deformation structures. Overall, the magmatic and the magnetic fabrics are broadly discordant with the metamorphic foliation of the country rocks, defining an EW trending elliptical asymmetric sill rooted in the SW quadrant. The reconstructed architecture combined to petrologic observation indicates that accretion of the pluton involved injection of multiple dykes through a sub-vertical feeder zone, combined to lateral flow of the roof controlled by inherited collisional structure. The duration of magmatic activity and the cooling history of the contact metamorphic aureole have been evaluated through a suite of 2D thermal models. All these observations, together with the available geochronological constraints are suggestive of very rapid construction of the pluton. The proposed emplacement model is fully consistent with the regional phase of strike-slip tectonics and widespread magmatism accommodating the large rotation of the Corsica-Sardinia block during the Carboniferous-Permian transition. [ABSTRACT FROM AUTHOR]

This paper deals with the geological mapping of the late-Variscan Sàrrabus pluton, (southeastern 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. [ABSTRACT FROM AUTHOR]

• The Montevecchio-Ingurtosu district was one of the largest Italian Pb-Zn-Ag producers. • New field, microscopic, microchemical, isotopic, and fluid inclusion data were obtained. • The Montevecchio deposit shows several affinities with the class of Ag-Pb-Zn veins in metasediments as defined by Beaudoin & Sangster (1992). • Ore textures and mineralogical-chemical features at all scales document a multistage process of mineralization postdating the emplacement of the 304 ± 4 Ma Arbus pluton, and occurring in a tectonically active regime. • The exact age of mineralization is not constrained, although it might be related to regional, large-scale shear deformation in a late-post-orogenic context. • At least part of the mineralization is associated with relatively low temperature (≦200 °C), high salinity (>20 wt% equiv. mass NaCl) fluids analogous to basinal brines. The Montevecchio-Ingurtosu district (SW Sardinia) was among the largest historical Pb-Zn producers of Italy, with significant Ag output, and yields of metallic byproducts such as Cd, Co, Cu, Bi, Sb, Ge, In, and Ga. Despite this importance, detailed descriptions of orebodies and mineral assemblages are surprisingly scarce and old. Here we summarize all previously available information and contribute new textural, microchemical, fluid inclusion, and C-O isotopic data deriving from a recent sampling of currently exposed orebodies. Mineralization occurs as steeply dipping veins extending for almost 20 km at the northern and western flanks of the Variscan Arbus pluton; veins are hosted in phyllites of the Arburese Unit close to the thermometamorphic aureole. Ore enrichments range from massive to coarsely nodular, stockwork and brecciated. Vein filling consists of siderite (locally Zn-rich), quartz, sphalerite, galena (remarkably rich in micro-inclusions), with accessory chalcopyrite, fahlore, bournonite, barite, and Ni-Co sulfarsenides. Vein assemblages may vary, even within a single vein, from sphalerite- to galena-dominated. Cu-rich assemblages (fahlore + chalcopyrite) were locally observed. Wallrock is affected by silicification, sericitization and pyrite dissemination. Sphalerite shows a complex mineral chemistry, with marked variations in Fe (0.08 to 8.9 mol% FeS) and in Cd contents (from <0.05 to >1 wt%). Trace element analyses (LA-ICP-MS) document the presence of measurable amounts of Ga, Ge, In, Ag, Ni, Co, Tl and Mo. Fahlore varies from the Sb (tetrahedrite) and the As (tennantite) endmembers, with Ag-rich compositions corresponding to Sb endmembers. The occurrence of Cd-rich tetrahedrite (up to 14.5 wt%) is remarkable. Fluid inclusion studies on sphalerite and quartz are in agreement with previous literature data, and indicate comparatively low (in the range 90°–130 °C) homogenization temperatures (T h) and high salinities (14 to 25 equiv. mass % NaCl); both microthermometric data and SEM/EDS analyses of decrepitated inclusions indicate the presence of Ca and K beside Na. Pressure correction to T h is presumably low (in the order of 10 °C), considering a hydrostatic pressure regime. Application of the sphalerite-based GGIMFiS thermometer provided temperatures in excellent agreement with fluid inclusion data for the Montevecchio mineralization. Isotopic data on Montevecchio carbonates define mildy negative δ13C PDB values (between −1 and −5 per mil), and a larger spread of δ18O SMOW values, between +14 and +20 per mil. Other isotopic data from literature include a limited set of δ34S values for galena, sphalerite and pyrite, and a fairly large body of Pb isotopic data on galena. Comparatively narrow ranges for sulfur isotope signatures suggest a homogeneous, possibly igneous, sulfur source, whereas the large spread in Pb isotope signatures reflects the large-scale character of the hydrothermal process and indicates that the Arbus pluton may have been just one of the sources of ore lead. The Montevecchio vein system shows affinities with other late to post Variscan European deposits. The nature of the mineralizing fluids at Montevecchio is analogous to low temperature, basinal brines, and typical of several regional-scale, late to post-Variscan hydrothermal events across Europe. Mineralization at Montevecchio obviously postdates the emplacement of the Arbus plutonic complex, but its exact age remains unknown.. [ABSTRACT FROM AUTHOR]

The Sàrrabus pluton is formed by multiple short-lived intrusions emplaced at about 286 Ma at shallow crustal levels within the external part of the South Variscan Orogenic Belt. A chemical and Sr and Nd isotopic study on the Variscan post-collisional magmatism from the Sàrrabus pluton reveals the repeated bimodal character of the intrusions, in which heterogeneous crustal sources and mantle-derived calcalkaline magmas are involved. Products of this magmatic activity occur as intrusive units and mafic/felsic dykes intruded in post-collisional regime along extensional faults during tectonic exhumation. Pluton growth started with an early stage of emplacement of broadly granodioritic magma with subordinate mafic magma batches (stage 1) followed by large intrusions of metaluminous to subaluminous and subordinately peraluminous granites (stage 2). In stage 1 , the occurrence of remnants of stratified olivine-bearing gabbroic rocks indicates the intrusion of mafic magmas which experienced low-pressure crystal/liquid fractionation. Mafic magmas may represent an external heat supply for melting of different crustal materials belonging to an inferred Precambrian crystalline basement underlying the Paleozoic rocks of the Variscan nappe pile. Strong evidence for heterogeneous crustal sources is constrained by isotope data. Peraluminous granites and felsic dikes display initial 87Sr/86Sr in the range of 0.7140÷0.7215 and a roughly constant εNd 286 (−7.4 to −7.5). Conversely, a peculiar less radiogenic character, in the range of 0.7030÷0.7067/−5.5÷ − 6.2, is observed for metaluminous to subaluminous varieties. Calculated Neodymium Crustal Index (NCI) confirmed a progressive increase in crustal magmas generation during the pluton growth, from stage 1 , recording minor mixing processes between mantle- and crustal-derived peraluminous melts, to stage 2 , where extensive crustal melting occurred, originating metaluminous to subaluminous granites. Possible crustal sources for metaluminous/subaluminous and peraluminous granites are (Pan-African) amphibolites and metasedimentary rocks, respectively. Two-stage depleted-mantle Nd model ages cluster at 1.4 and 1.6 Ga for metaluminous/subaluminous and peraluminous granites, respectively, well comparable with other segments of the European Variscan belt. Remarkably, last magmatic pulses resulted in widespread subalkaline bimodal mafic/felsic dykes that overlapped the Sr Nd signature recorded by major intrusions. This similar geochemical affinity between late dykes and the first intrusives may be related to decreasing temperature in the crust, which inhibited extensive mixing processes with the upwelling melts. At the same time, the presence of felsic intrusions in the shallow crust would have prevented the rise of more primitive basic magmas, which would have consolidated at depth. Finally, the high radiogenic character of Sàrrabus mafic products, compared to coeval Variscan mafic rocks of Corsica and northern Sardinia, may be indicative of previous fractionation and mixing processes, possibly related to magmatic underplating of the lower crust. • The Sàrrabus pluton is formed by multiple short-lived intrusions at ca. 286 Ma. • Pluton growth started with an early stage of broadly granodioritic composition. • Large intrusions of metaluminous to subaluminous granites follow the granodiorites. • During the pluton growth, a progressive increase in crustal magmas generation occurred. • Last magmatics are subalkaline mafic/felsic dikes with major intrusions signature. [ABSTRACT FROM AUTHOR]