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Deformazione finita della fase D1 dell'orogenesi alpina in Toscana meridionale: contributo dall'analisi delle reduction spot nell'Unità di Monticiano-Roccastrada
No full textThe composite shear frame in the Variscan belt of Sardinia (Italy): implications in the emplacement of HJT rocks.
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Late Hercynian shear zones in Sardinia
No full textIn the past few years two main late Hercynian shear zones have been identified in Sardinia: the Mount Grighini shear zone in the centre of the island and the Posada Valley shear zone in the north. Both are dextral wrench shear zones, affecting the Hercynian basement during the Late Carboniferous, and characterized by a simple shear deformation with an evolution from cataclastic to ultramylonitic rocks. The meso-and microstructural deformation features are discussed here. On the basis of these, two maps of the different deformative zones within the shear zones have been prepared and both displacements have been calculated. An attempt has also been made to correlate with other late Hercynian shear zones in continental Europe on the basis of common features and geological constraints
The Corsica-Sardinia Massif as source area for the early northern Apennines foredeep system: evidence from debris flows in the “Macigno costiero” (Late Oligocene, Italy)
No full textLarge isolated gravity flows (debrites) are widely present in the stratigraphic record of the northern Apennines foreland-basin system. These strata may be useful for provenance signals and dispersal pathways during foreland evolution. This paper examines a cohesive debris flow bed interbedded with turbidite strata of the Macigno Formation (Late Oligocene, Tuscany, Italy), in order to obtain new data on the provenance of the elastic material. Clasts in the debris flow are predominantly plutonic (granodiorite, tonalite, and S-granite) and subordinately metamorphic (gneiss and schist) and sedimentary calcareous clasts. The composition of the clasts within the debris flow is similar to the clastic composition of the interbedded turbidite sandstones of the "Macigno costiero." The depositional features of the debris flow suggest that it traveled for a short distance within the basin before it was deposited not far from the slope. The absence of a high-pressure/low-temperature (HP/LT) paragenesis in the plutonic and metamorphic clasts of the debris flow indicates a provenance from a crystalline basement not involved in the high-pressure phases of the Alpine Orogenesis. Previous studies have indicated the Central-Western Alps as potential source areas for the Macigno Formation sediments. The lack of HP/LT tuetamorphic signatures in our studied samples excludes the Pennidic aud Austroalpine nappes of the Western Alps as possible sources for the debris flows of the "Macigno costiero." These new data (sedimentological, petrographical, and microstructural) suggest that the Corsica-Sardinia Hercynian basement, lacking a HP/LT paragenesis, is the more accredited source area of the debris flow and of the related turbidite sandstones of the "Macigno costiero" succession. These foredeep-feeding sediments were probably before deposited within an episutural basin developed close to the northern Apennines orogenic wedge
The Variscan (?) Settiballas micaschists (SW Sardinia): geological and petrographical investigation
No full textGiant garnet crystals in wollastonite–grossularite–diopside-bearing marbles from Tamarispa (NE Sardinia, Italy): geosite potential, conservation, and evaluation as part of a regional environmental resource
No full textThe wollastonite–garnet–diopside-bearing marbles cropping out in the Migmatite Complex west to the Tamarispa and San Lorenzo villages share a common metamorphic and deformational history with the surrounding migmatite, with metamorphic peak conditions between 650 and 850 °C. Within the marble, there is an interesting and rare garnet mineralization. The peculiar characteristic and geological–cultural and touristic attraction of this geosite is the presence of large garnet crystals (up to 20 cm). The whitish rock matrix is characterized by coarse-grained rock-forming minerals (mainly wollastonite, calcite, diopside and subordinately pectolite, quartz, plagioclase, epidote, apatite, titanite) with a compositional layering and a weak foliation (S2 schistosity), parallel to that of the surrounding gneiss and migmatites. At the outcrop scale, the giant garnet crystals often show a brown core in high relief surrounded by a darker rim with less relief. Under conservation state, the wollastonite–garnet–diopside-bearing marbles show an evident differential alteration with dissolution processes of the matrix and an increasingly pronounced enucleation of the garnet crystals. The Tamarispa outcrop with spectacular giant garnet crystals is here proposed as a new, potential geosite relevant for didactic, cultural, and touristic purposes. Conservation and valorization aspects are discussed within the more general framework of the geological, natural, and environmental resources of the local territory
Amphibole and Al-silicate bearing migmatites from NE Sardinia: partial melting of ordovician igneous source and sedimentary cover
No full textAmphibole- and Al-silicate-bearing migmatites from NE Sardinia: Partial melting of Ordovician igneous source and sedimentary cover
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