1,721,052 research outputs found
Evoluzione T-P di alcune metamorfiti mineralizzate a scheelite dell'Unita' Aspromonte (Arco Calabro-Peloritano).
No full textThe 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.
No full textCaratteri del metamorfismo ercinico nella fillade sudalpina ad ovest di Bressanone.
No full textThe aim of this paper is to contribute to the solution of the numerous problems concerning the South-Alpine crystalline basement of the Eastern Alps. An area located west of Bressanone (Brixen) (Fig. 1) was considered and the petrographic and microtextural features of its metapelites analyzed. The main rock-types are quartz-phyllites and phyllitic schists, within which metarhyolites ("porphyroids"), quartzites and metabasites are interlayered.
The distinction between the upper ("M. Cavallino Formation", "M. Cane Phyllites") and the lower ("Bressanone Phyllites") phyllitic complex is only possible according to mesostructural criteria: the metapelites making up the two complexes do display identical micro- and mesoscopic features. In particular, the almandine-biotite phyllites, which display the most complicated tectono-metamorphic history, have identical mineral assemblages in the two rock complexes, identical chemistry of the main mineral phases (Tables 1-4) and identical microtextural relationships between crystallization and deformation.
The tectono-metamorphic history of the considered metapelites was reconstructed. It consists of five crystallization stages, including two thermal climaxes which correspond to the higher-temperature part of the greenschists facies. The mineral compatibilities of each crystallization stage were also ascertained (Figs. 8-11).
Geothermometric estimations were deduced from the prevailing mineral assemblages (Fig. 13). Geobarometric estimations were based on the b value of the potassic white micas: the mean b value (8.774A) indicates low-pressure conditions of about 3 Kb. Considering the pattern of the b isopleths in the P-T field, an approximate value of 40°C/Km was assigned to the metamorphic thermal gradient of the Hercynian event
Sulla variabilità compositiva delle miche nell'ambito dello stesso affioramento di metapeliti di basso grado: un esempio. 1:Le biotiti.
No full textTertiary S-C mylonites from the well Bajansenye, Western Hungary
No full textUltramylonites and margarite-bearing quartz-feldspar S-C mylonites, containing amphibolite
lenses with symplectitic texture, were encountered in a borehole (Bajánsenye-B-M-I) close to the west
of the Transdanubian Central Range Unit. These rocks demonstrate a ductile, horizontal extensional
shear zone attaining a thickness of 300 m. Microstructural data, mineral parageneses and mineral
chemistry of these rocks indicate a multistage metamorphic evolution, which is consistent with that
of the Koralm-Pohorje basement. The youngest mylonitic event (Early Tertiary) took place in the
Bajánsenye mylonites at 430-450 °C (greenschist-facies); it rejuvenated coarse-grained muscovite
crystals of eo-Alpine age (Early-Middle Cretaceous). The radiometric data presented in this paper
demonstrate for the first time an important Early Tertiary tectonic zone in this area
Further data on the pre-Alpine metamorphic pressure conditions of the Austridic phyllitic complexes in the Eastern Alps.
No full textSpecial Volume of IGCP Project No 27
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