323 research outputs found
Clockwise and anticlockwise P-T path in the axial zone of the Variscan Sardinia-Corsica block
No full textRecent petrological studies on the Axial Zone of the Variscan chain have revealed the occurrence of anticlockwise P-T trajectories in metamorphic rocks from Corsica and Sardinia. These new findings, at first glance, appears to be in contrast with the clockwise P-T paths classically described for several high-pressure metamorphic rocks from the Variscan Sardinia - Corsica block in the last decades.
For the first time in Variscan Corsica, Massonne et al. (2018) described the anticlockwise P-T path of micaschists from the Porto Vecchio region. These rocks underwent prograde metamorphism starting at 3 kbar/600°C and then reached peak metamorphic conditions at 7 kbar/600-630°C. The Porto Vecchio micaschists are bordered to the north by the Solenzara-Fautea metamorphic rock unit that is, in turn, characterized by migmatites and granulites that underwent a clockwise P-T loop related to burial of continental crust to high-pressure (1.8–1.4 GPa) followed by high- to ultrahigh-temperature conditions (900–1000 °C; Giacomini et al., 2008). New, preliminary results on these rocks reveal that these latter peak temperatures could be probably significantly lower than those above mentioned, but there is no doubt about the clockwise shape of their P-T path. In the neighbouring Variscan terrains of north-eastern Sardinia, Scodina et al. (2019) reconstructed the P-T history of an amphibolite body whose burial path started at 0.8 GPa and was then followed by a slight increase in temperature up to peak metamorphic conditions of 1.3–1.4 GPa/690–740 °C. These amphibolites are hosted by migmatites for which a clockwise P-T path, related to a nearly isothermal exhumation, is widely accepted in the literature and confirmed by the most recent studies (Massonne et al., 2013 and references therein). In conclusion, it thus appears that during the Variscan collision, rock slices of different crustal levels were brought together and metamorphic rocks from upper and lower plates were involved in a particle path along an exhumation channel.
Giacomini F., Dallai L., Carminati E., Tiepolo M. & Ghezzo C. 2008. Exhumation of a Variscan orogenic complex: Insights into the composite granulitic–amphibolitic metamorphic basement of southeast Corsica (France).J. Metam. Geol., 26, 403–436.
Massonne H.-J., Cruciani G. & Franceschelli M. 2013. Geothermobarometry on anatectic melts - a high-pressure Variscan migmatite from northeast Sardinia. Int. Geol. Rev., 55, 1490–1505.
Massonne H.-J., Cruciani G., Franceschelli M. & Musumeci G. 2018. Anticlockwise pressure–temperature paths record Variscan upper-plate exhumation: example from micaschists of the Porto Vecchio region, Corsica. J. Metam. Geol., 36, 55–77.
Scodina M., Cruciani G., Franceschelli M. & Massonne H.-J. 2019. Anticlockwise P-T evolution of amphibolites from NE Sardinia, Italy: geodynamic implications for the tectonic evolution of the Variscan Corsica-Sardinia block. Lithos, 324–325, 763–775
CARMIGNANI L., FRANCESCHELLI M., GHEZZO C., MEMMI I., PERTUSATI P.C. RICCI C.A. (1981)- Some PT time path recorded in the Sardinia metamorphic basement. Terra Abstract EUG I, Strasbourg
No full textFerrimuscovite and celadonite substitutions in muscovite from Fe3+-rich low-grade psammitic rocks (Northern Apennines,Italy)
No full textElectron microprobe and wet-chemical data of muscovites from pyrophyllite- or K-feldspar-bearing Fe3+-rich rocks of the Verrucano metasediments are reported. A close relationship has been found between muscovite composition and bulk-rock chemistry. The extent of celadonite and ferrimuscovite substitutions increases progressively from pyrophyllite- to K-feldspar-bearing samples. The mutual cation substitutions reveal: (1) an almost ideal Tschermak substitution; (2) a close positive correlation between the (Mg + Fe2+) and Fe3+ contents; and (3) a negative correlation between the octahedral and interlayer occupancies. The extent of celadonite and ferrimuscovite substitutions of muscovite from magnetite-bearing rocks has been constrained at moderate pressure in low-temperature metamorphism. © 1989
Studio antropologico dei resti umani dell’area cimiteriale di Ostra
No full textSulle colline dell’entroterra marchigiano, in prossimità dell’attuale città di Ostra Vetere, in provincia di Ancona, sorgono le rovine della città romana di Ostra antica. Situata su un ampio terrazzo alluvionale del fondovalle, alla sinistra del fiume Misa (l’antico fiume Sena), la cui valle rientrava in un sistema di collegamento tra il versante adriatico e quello tirrenico, che dunque metteva questo settore in diretto contatto con Roma, la città di Ostra rivestiva una valenza strategica di primaria importanza. Ed è proprio a causa della sua posizione geograficamente vantaggiosa che ben presto Ostra divenne territorio romano, praefectura prima e municipium in seguito (Dall’Aglio et alii 2014).
Le campagne archeologiche condotte in questo sito, oggi denominato “Le Muracce”, dalla Soprintendenza per i Beni Archeologici delle Marche tra il 1985 e il 1990, e riprese dall’Università di Bologna dal 2006, sotto la direzione di Pier Luigi Dall’Aglio, hanno portato alla luce una serie di edifici, datati tra il III secolo a.C. e il V secolo d.C., che si affacciavano sull’area forense. Tra il VI e il VII secolo queste strutture vennero abbandonate e i pavimenti, i lastricati e le fosse di spoliazione furono utilizzati come piano deposizionale per un cospicuo numero di sepolture che andarono a costituire una vera e propria area cimiteriale, sfruttata dal tardoantico all’altomedioevo (Dall’Aglio et alii 2014; Dall’Aglio, Franceschelli, TassSSinari 2014b) (Fig. 1).
I resti scheletrici degli inumati recuperati dalla suddetta area cimiteriale sono stati oggetto di uno studio archeo-antropologico, svolto presso il Laboratorio di Antropologia fisica del Dipartimento di Beni Culturali dell’Università di Bologna (Campus di Ravenna), che ha avuto lo scopo di ricostruire le caratteristiche antropologiche, la struttura demografica, le condizioni di vita e di salute degli abitanti della città tardoantica di Ostra, anche in un quadro comparativo con altre comunità del medesimo territorio
Geochemistry and mineralogy of detritic rocks from Verrucano type-sequences of Northern Apennines (Monti Pisani and Punta Bianca), Italy
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Crystallinity distribution and crystallinity-b0 relationships in white K-micas of Verrucano metasediments (northern Apennines, Italy)
No full textb0 of muscovite in low and high variance assemblages from low grade Verrucano rocks, Northern Apennines, Italy
No full textA note on the occurrence and chemistry and K/Ar data of stilpnomelane from Mt. Contrario (Apuan Alps, Northern Tuscany)
No full textb0 of muscovite in low and high variance assemblages from low grade Verrucano rocks, northern Apennines, Italy
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