Permian high-temperature metamorphism in the Western Alps (NW Italy)

During the late Palaeozoic, lithospheric thinning in part of the Alpine realm caused high-temperature low-to-medium pressure metamorphism and partial melting in the lower crust. Permian metamorphism and magmatism has extensively been recorded and dated in the Central, Eastern, and Southern Alps. However, Permian metamorphic ages in the Western Alps so far are constrained by very few and sparsely distributed data. The present study fills this gap. We present U/Pb ages of metamorphic zircon from several Adria-derived continental units now situated in the Western Alps, defining a range between 286 and 266 Ma. Trace element thermometry yields temperatures of 580-890°C from Ti-in-zircon and 630-850°C from Zr-in-rutile for Permian metamorphic rims. These temperature estimates, together with preserved mineral assemblages (garnet-prismatic sillimanite-biotite-plagioclase-quartz-K-feldspar-rutile), define pervasive upper-amphibolite to granulite facies conditions for Permian metamorphism. U/Pb ages from this study are similar to Permian ages reported for the Ivrea Zone in the Southern Alps and Austroalpine units in the Central and Eastern Alps. Regional comparison across the former Adriatic and European margin reveals a complex pattern of ages reported from late Palaeozoic magmatic and metamorphic rocks (and relics thereof): two late Variscan age groups (~330 and ~300 Ma) are followed seamlessly by a broad range of Permian ages (300-250 Ma). The former are associated with late-orogenic collapse; in samples from this study these are weakly represented. Clearly, dominant is the Permian group, which is related to crustal thinning, hinting to a possible initiation of continental rifting along a passive margin

Groundwater-level risk assessment by using statistical and geographic information system (GIS) techniques: a case study in the Aosta Valley region, Italy

In the present study, groundwater-level monitoring has been carried out on 26 observation dug wells in the Aosta Valley region, Italy, during the dry season (June 2013) and wet season (November 2013) in order to assess the water-level fluctuation (WLF). The depth to water level varied from 3.04 to 28.70 metres below ground level (mbgl) in the dry season and from 2.92 to 25.62 mbgl in the wet season. The WLF of the study area varied from 0.01 to 6.80 mbgl, and the western and north-western regions of the study area showed higher WFL. The WLF map was validated with a statistical analysis and elevation value of the area in a geographic information system environment, and this indicated that validation can be accepted for the WLF in the Aosta Valley. The results of the study demonstrated that the eastern region could be considered as a safe and good recharge zone for the groundwater in the Aosta Valley region. The WLF map generated in this study could also be used for the management of future groundwater resources and environmental planning of the area

Geologia di una traversa dal Gran Paradiso alla Zona Sesia-Lanzo in alta val Soana, Piemonte

La Val Soana, tributaria di sinistra della Val dell\u2019Orco, \ue8 situata nelle Alpi Graie piemontesi al margine nordorientale del massiccio del Gran Paradiso e costituisce una sezione naturale di particolare interesse attraverso la catena collisionale continentale. La pila delle falde \ue8 costituita dalle unit\ue0 tettoniche seguenti, in successione dal basso verso l\u2019alto: 1) la falda del Gran Paradiso, un frammento di crosta continentale pennidica di provenienza paleo europea; 2) la Zona piemontese dei calcescisti con pietre verdi, insieme composito di unit\ue0 ofioliti che ad affinit\ue0 oceanica e metamorfismo eclogitico e di falde di scollamento a dominanti calcescisti in facies scisti verdi; 3) il Klippe del Santanel ed il margine occidentale della Zona Sesia-Lanzo, unit\ue0 austro alpine di provenienza paleo africana (apula), il primo con micascisti eclogitici fortemente retrocessi, la seconda con gneiss minuti albitici e microocchiadini in facies scisti verdi. Tra le litologie delle unit\ue0 oceaniche piemontesi si segnalano micascisti granatiferi a clorito ide e quarziti manganesifere nelle sequenze sopraofiolitiche, pillowlave e brecce glaucofanitiche, eclogiti da protoliti basaltici e Fe-Ti-gabbrici e scaglie di serpentiniti a noduli di olivina e titanclinohumite di neoformazione. Il metamorfismo in facies scisti verdi dell\u2019evento medio-terziario lepontino \ue8 distribuito in forma generalmente pervasiva in tutte le unit\ue0 tettoniche ed \ue8 posteriore all\u2019appilamento delle falde. L\u2019evento eoalpino di alta pressione e bassa temperatura, presente solo in alcune unit\ue0 continentali ed oceaniche, \ue8 anteriore alla struttura collisionale a falde appilate. In particolare si osservano due paia di unit\ue0 tettoniche che, formate ciascuna da un elemento continentale e da uno oceanico, sono entrambe eclogitiche ed accoppiate in una fase precoce dell\u2019evoluzione compressionale. Esse sono separate da una falda di scollamento di calcescisti con subordinate meta ofioliti in facies scisti verdi e sovra scorse da una coppia sommitale di unit\ue0 in facies scisti verdi, costituite da calcescisti e dagli gneiss minuti Sesia-Lanzo. La presenza di unit\ue0 eclogitiche alternate ad unit\ue0 non eclogitiche nella pila delle falde della Val Soana richiede un forte raccorciamento crostale durante l\u2019evento lepontino e l\u2019imbricazione di unit\ue0 esumate da livelli profondi con unit\ue0 confezionate a livelli superficiali

Geology and evolution of the Northern Adriatic structural triangle between Alps and Apennine

The basic kinematic evolution leading to the present tectonic setting of the Northern Adriatic zone is here synthetically outlined. The Adriatic domain is the structural area progressively invaded by neighboring orogenic chains. The evolution of the Southern Alps and of the Northern Apennines from the beginning of the Neogene time onward is here summarized. Orogenic processes due to plate convergence or to orogenic and magmatic arc evolution are here compared and discussed in the frame of Western Mediterranean genesis