247 research outputs found
Evoluzione T-P di alcune metamorfiti mineralizzate a scheelite dell'Unita' Aspromonte (Arco Calabro-Peloritano).
No full textThe Basement Complexes in Italy, with special regards to those exposed in the Alps: a review
No full textMost of the sedimentary rocks occurring in Italy are
post-Carboniferous. All what lies below is considered
basement, mostly metamorphic or igneous. Understanding
the pre-Carboniferous evolution depends on the
reconstruction of the sedimentary, metamorphic and
igneous evolution of the basement. In general, the basement
sedimentary protoliths were Lower to Middle Paleozoic
siliciclastic rocks, while the igneous protoliths
belong to an Ordovician cycle. The prevailing metamorphism,
from very-low grade to granulite facies, is
Variscan. It was followed by the formation of large
amounts of granitic melts
Simultaneous measurements of chlorite and illite crystallinity: a more reliable tool for monitoring low- to very low grade metamorphisms in metapelites. A case study from the South-Alpine basement of the Eastern Alps (Italy).
No full textGeo-petrographic data on the metamorphic rocks with Cambrian, Silurian and Devonian fossils in the Agordo area (Southalpine metamorphic basement of the Eastern Alps, Italy).
No full textRecently, in the Agordo area, some unquestionable fossils have been described: 1) Latest Cambrian acritarchs,
within trivial black, fine grained phyllites (Col di Foglia); 2) Aeronian graptolites, within boudins along a recrystallized shear
zone cutting low-grade metapelites (Ponte Alto); 3) Middle Devonian Rugosa corals, within metalimestone boudins along
the mentioned shear zone. These fossil findings are unique in this basement, therefore, the rocks containing them deserve
a careful petrographic investigation. This paper presents the basic petrographic features of the rock samples containing
the fossils. All the rocks underwent a greenschist facies metamorphism (chlorite zone) under a thermal gradient of ca.
38°C/Km. The most interesting rocks are those bearing well preserved graptolites which mainly consist of quartz,
fluorapatite (up to 70%.), carbonaceous matter and sulphides. T in the boudins turns out to be slightly lower than in the
surrounding matrix
Petrography of the metamorphic rocks from the Agordo area bearing latest Cambrian, Aeronian and Devonian fossils (Southalpine metamorphic basement of the Eastern Alps, Italy).
No full textAbstrac
The baric character of the Patagonian basement as deduced from the muscovite spacing: a first contribution from Eastern Andean Metamorphic Complex (Andes, Chile)
No full textIn this work we present new data concerning the pressure character of metamorphism in the Aysén Eastern
Andean Metamorphic Complex. The parameter d060,33
–
1 of the K-white mica from basement pelitic rocks was measured
as a barometric indicator. Three sample groups from different areas were considered, for a total of 69 samples.
All measured values suggest a metamorphic setting characterised by intermediate to high pressure.
Key-words: white micas, d060,33–1 parameter, pressure character, Aysén metamorphic Complex
On the compositional variability of metamorphic chlorites as an effect of the micro-site chemistry. Rend. Fis. Acc. Lincei, 9, 8, 77-93.
No full textThe "Venice Granodiorite": its features and consequent constraints on the "Caledonian" and Variscan events in the Alpine domain
No full textAn Ordovician granodiorite body was sampled along an exploratory well in the Northern
Adriatic Sea, close to the Lagoon of Venice. It stands 4711 m below the sea floor, and is buried under a sedimentary
cover spanning from Triassic to Quaternary. It contains several metasedimentary xenoliths, as well as
some microgranular enclaves. The drilled core is a unique example of the Southalpine crystalline basement under
the Po Plain. The granodiorite is undeformed, and does not display post-emplacement metamorphic overprints.
It therefore limits southwards the possible extent of the Variscan orogenic belt, which is well documented
in the Southalpine and Austridic metamorphic basements. The granodiorite is classified as an S-type granitic
rock, on the basis of major and trace element geochemistry and the occurrence of abundant metasedimentary
xenoliths. These features, together with the isotopic signatures, point to an anatectic origin of the granodiorite.
The metamorphic xenoliths are probably fragments from the wall-rocks of the pluton, and do not represent
restites of the main crustal source of the granodiorite. The microgranular enclaves probably represent parts of
chilled margins disrupted within the pluton, and do not indicate interaction with more mafic, mantle-derived
melts. The representative points of the granodiorite plot in post-collisional fields in some discriminant diagrams.
The age and many geochemical features of the Venice granodiorite are similar to those of the Austridic
metamorphosed granitoids occurring in the Eastern Alps, possibly indicating a unique geodynamic setting for
their genesis and emplacement. Together with the coeval calc-alkaline, mostly mantle-derived metagranitoids
occurring in the «Serie dei Laghi» (Western Southalpine), they define a magmatic suite which is consistent with
a convergent plate boundary tectonic setting
Pressure character of the Variscan metamorphism in the Gemericum and Veporicum (West Carpathians, Czecho-Slovakia).
No full textSulla variabilità compositiva delle miche nell'ambito dello stesso affioramento di metapeliti di basso grado: un esempio. 2: Le muscoviti e considerazioni conclusive. Rend. Fis. Acc. Lincei, IX, 3, 1, 43-55.
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