Heterogeneous brittle-ductile deformation at shallow crustal levels under high thermal conditions: The case of a synkinematic contact aureole in the inner northern Apennines, southeastern Elba Island, Italy

In extensional tectonic settings, stretched terrains are often associated to lithosphere partial melting and widespread magmatism with plutons emplaced in the thinned crust. Emplacement of felsic magmas, at upper crustal levels, represents the final stage of the magma transfer from profound to shallow depth. In this framework, a mostly vertical permeability controls the magma uprising migration, as induced by dominant transcurrent crustal structures. Nevertheless, the interplay between extension and prolonged heat transfer favors uplift and progressive exhumation of the magmatic bodies, during their cooling.In this presentation, we show an example of a felsic magmatic intrusion, the Porto Azzurro pluton (inner northern Apennines), emplaced in an extensional tectonic setting and mainly controlled by a regional transfer zone related to the opening of the Tyrrhenian Basin. This is exposed in the eastern Elba Island (Tuscan Archipelago). The hosting rocks of the Porto Azzurro pluton are mainly represented by micaschist, paragneiss and quartzite, affected by contact metamorphism and intense fluid circulation. We have analysed the structures that assisted the pluton emplacement and the ones that deformed the pluton itself during its cooling, from melt-present to brittle conditions, based on the integration among fieldwork, micro-structural, petrological and EBSD analyses. Furthermore, new U/Pb geochronological data on zircons and (U-Th)/He on apatite fission track refined the age of the pluton emplacement and its cooling, adding new data about the pluton history. Existing petrological analyses of the hosting rocks allowed us to better constrain the time-evolution of the thermal perturbation, permitting to frame the deformation and exhumation history of the Porto Azzurro monzogranite in the context of the Neogene extensional tectonics affecting the inner Northern Apennines.

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Multiple hydro-fracturing by boron-rich fluids in the Late Miocene contact aureole of eastern Elba Island (Tuscany, Italy)

Terra Nova ◽

10.1111/j.1365-3121.2008.00823.x ◽

2008 ◽

Vol 20 (4) ◽

pp. 318-326 ◽

Cited By ~ 29

Author(s):

A. Dini ◽

F. Mazzarini ◽

G. Musumeci ◽

S. Rocchi

Keyword(s):

Late Miocene ◽

Contact Aureole ◽

Elba Island

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HP-LT metamorphism in Elba Island: Implications for the geodynamic evolution of the inner Northern Apennines (Italy)

Journal of Geodynamics ◽

10.1016/j.jog.2015.08.001 ◽

2015 ◽

Vol 91 ◽

pp. 13-25 ◽

Cited By ~ 21

Author(s):

Caterina Bianco ◽

Andrea Brogi ◽

Alfredo Caggianelli ◽

Giovanna Giorgetti ◽

Domenico Liotta ◽

...

Keyword(s):

Northern Apennines ◽

Geodynamic Evolution ◽

Elba Island

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Late Miocene constrictional strain in the northern Apennines: A case study from the Barabarca metaconglomerate (Elba Island, Italy)

Geological Journal ◽

10.1002/gj.3793 ◽

2020 ◽

Vol 55 (9) ◽

pp. 6325-6337

Author(s):

Samuele Papeschi

Keyword(s):

Late Miocene ◽

Northern Apennines ◽

Elba Island

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Strain-induced phase changes within cold basal ice from Taylor Glacier, Antarctica, indicated by textural and gas analyses

Journal of Glaciology ◽

10.3189/172756505781829098 ◽

2005 ◽

Vol 51 (175) ◽

pp. 611-619 ◽

Cited By ~ 13

Author(s):

Denis Samyn ◽

Sean J. Fitzsimons ◽

Reginald D. Lorrain

Keyword(s):

Thermal Conditions ◽

Significant Loss ◽

Phase Changes ◽

Ductile Deformation ◽

Geochemical Evolution ◽

Gas Composition ◽

Outlet Glacier ◽

Basal Ice ◽

Gas Measurements ◽

Taylor Glacier

AbstractThis paper reports detailed textural and gas measurements conducted in cold basal ice (–17°C from the margin of Taylor Glacier, an outlet glacier of the East Antarctic ice sheet. The analyzed samples were retrieved from a basal ice sequence excavated at the end of a subglacial tunnel dug near the glacier snout. The basal sequence exhibits two contrasting ice facies, defined as the englacial and stratified facies. On the one hand, analysis of ice crystal textures from the basal ice sequence provides evidence for localized ductile deformation, especially within the stratified facies where significant dynamic recrystallization was detected. On the other hand, high-resolution gas analyses reveal that strong changes in gas composition occurred at the structural interfaces of the stratified facies. These gas composition changes are typical of melting–refreezing processes but are not associated with any significant loss of gas volume. Given the specific subglacial thermal conditions at the margin of Taylor Glacier, we interpret this phenomenon as resulting from microscopic phase changes involving selective gas redistribution through the pre-melt phase. It is argued that such processes may play an important role in the post-genetic geochemical evolution of cold debris-laden ice and may be enhanced through intense strain conditions.

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Reconsidering the Variscan basement of southern Tuscany (inner Northern Apennines)

10.5194/egusphere-egu21-1675 ◽

2021 ◽

Author(s):

Enrico Capezzuoli ◽

Amalia Spina ◽

Andrea Brogi ◽

Domenico Liotta ◽

Gabriella Bagnoli ◽

...

Keyword(s):

Continental Crust ◽

Early Carboniferous ◽

Northern Apennines ◽

Time Interval ◽

Structural Studies ◽

Structural Setting ◽

Elba Island ◽

Orogenic Cycle ◽

Existing Data ◽

Variscan Basement

The Pre-Mesozoic units exposed in the inner Northern Apennines mostly consist of middle-late Carboniferous-Permian successions unconformably deposited on a continental crust consolidated at the end of the Variscan (i.e. Hercynian) orogenic cycle (Silurian-Carboniferous). In the inner Northern Apennines, exposures of this continental crust, Cambrian?-early Carboniferous in age, have been described in the Northern Tuscany, Elba Island (Tuscan Archipelago) and, partly, in scattered and isolated outcrops of southern Tuscany. In this contribution, we reappraise the most significative succession (i.e. Risanguigno Formation) exposed in southern Tuscany and considered by most authors as part of the Variscan Basement. New stratigraphic and structural studies, coupled with palynological analyses, allow us to refine the age of the Risanguigno Fm and its geological setting and evolution. Based on the microfloristic content, the structural setting and the fieldwork study, we attribute this formation to late Tournaisian-Visean (middle Mississipian) time interval and conclude it is not showing evidence of a pre-Alpine deformation. These results, together with the already existing data, allow us to presume that no exposures of rocks involved in the Variscan orogenesis occur in southern Tuscany.

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Early Palaeozoic intracratonic shears and post-tectonic cooling in the Rauer Group, Prydz Bay, East Antarctica constrained by40Ar/39Ar thermochronology

Antarctic Science ◽

10.1017/s0954102007000478 ◽

2007 ◽

Vol 19 (3) ◽

pp. 339-353 ◽

Cited By ~ 29

Author(s):

Christopher J.L. Wilson ◽

Cameron Quinn ◽

Laixi Tong ◽

David Phillips

Keyword(s):

Structural Evolution ◽

Thermal Conditions ◽

Shear Zones ◽

Ductile Deformation ◽

Prydz Bay ◽

Cooling Rates ◽

Deformation Event ◽

Thermal Histories ◽

Early Palaeozoic ◽

Field Variability

AbstractThe Rauer Group, in Prydz Bay, contains reworked Archaean-Proterozoic crust in high-strain zones that formed during a pervasive high-temperature ductile deformation event related to intracratonic mechanisms. The effects of this event extend southwards from Prydz Bay into the southern Prince Charles Mountains. The associated structural evolution involved development of ductile and brittle structures that formed during an approximately north–south directed transpressional deformation event that is confined to high-grade (>800°C) shear zones in the Rauer Group. Minerals from the Rauer Group, yield40Ar/39Ar cooling ages ranging from 560 to 460 Ma. Thermal histories derived from hornblende, biotite and feldspar suggest that the onset of rapid cooling began sometime prior to 510 Ma with cooling rates ofc. 42 to 33°C myr-1fromc. 510 Ma toc. 500 Ma. Whereas,40Ar/39Ar data obtained from plagioclase and K–feldspar suggest a slower cooling fromc. 500 Ma toc. 460 Ma with cooling rates from 5 to 2°C myr-1. These results demonstrate that the early Palaeozoic cooling history and comparable palaeostress regimes are regionally extensive, which has important implications for the tectonothermal and stress-field variability across Gondwana. The elevated thermal conditions would induce lithospheric weakening and promote the early Palaeozoic intraplate orogeny observed in eastern Antarctica with the development of a large intracratonic shear system.

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