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

<p>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.</p><p>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.</p>

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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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The magmatic evolution of the late Miocene laccolith–pluton–dyke granitic complex of Elba Island, Italy

Geological Magazine ◽

10.1017/s0016756802006556 ◽

2002 ◽

Vol 139 (3) ◽

pp. 257-279 ◽

Cited By ~ 94

Author(s):

A. DINI ◽

F. INNOCENTI ◽

S. ROCCHI ◽

S. TONARINI ◽

D. S. WESTERMAN

Keyword(s):

Late Miocene ◽

Dyke Swarm ◽

Short Time Span ◽

Variable Nature ◽

Mantle Sources ◽

Magma Sources ◽

Igneous Activity ◽

Mafic Magmas ◽

Elba Island ◽

Short Time

Since late Miocene time, post-collisional extension of the internal parts of the Apennine orogenic belt has led to the opening of the Tyrrhenian basin. Extensive, mainly acidic peraluminous magmatism affected the Tuscan Archipelago and the Italian mainland during this time, building up the Tuscan Magmatic Province as the fold belt was progressively thinned, heated and intruded by mafic magmas. An intrusive complex was progressively built on western Elba Island by emplacement, within a stack of nappes, of multiple, shallow-level porphyritic laccoliths, a major pluton, and a final dyke swarm, all within the span from about 8 to 6.8 Ma. New geochemical and Sr–Nd isotopic investigations constrain the compositions of materials involved in the genesis of the magmas of Elba Island compared to the whole Tuscan Magmatic Province. Several distinct magma sources, in both the crust and mantle, have been identified as contributing to the Elba magmatism as it evolved from crust-, to hybrid-, to mantle-dominated. However, a restricted number of components, geochemically similar to mafic K-andesites of the Island of Capraia and crustal melts like the Cotoncello dyke at Elba, are sufficient to account for the generation by melt hybridization of the most voluminous magmas (c. εNd(t) −8.5, 87Sr/86Sr 0.715). Unusual magmas were emplaced at the beginning and end of the igneous activity, without contributing to the generation of these hybrid magmas. These are represented by early peraluminous melts of a different crustal origin (εNd(t) between −9.5 and −10.0, 87Sr/86Sr variable between 0.7115 and 0.7146), and late mantle-derived magma strongly enriched in incompatible elements (εNd(t) = −7.0, 87Sr/86Sr = 0.7114) with geochemical–isotopic characteristics intermediate between contemporaneous Capraia K-andesites and later lamproites from the Tuscan Magmatic Province. Magmas not involved in the generation of the main hybrid products are not volumetrically significant, but their occurrence emphasizes the highly variable nature of crust and mantle sources that can be activated in a short time span during post-collisional magmatism.

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