Syn‐Orogenic Exhumation of High‐P Units by Upward Extrusion in an Accretionary Wedge: Insights From the Eastern Elba Nappe Stack (Northern Apennines, Italy)

Abstract

Exhumed high-pressure/low-temperature (HP-LT) rocks and terranes occur worldwide in both active and fossil collision zones reflecting complex subduction zone processes (

Cyclic Brittle‐Ductile Oscillations Recorded in Exhumed High‐Pressure Continental Units: A Record of Deep Episodic Tremor and Slow Slip Events in the Northern Apennines

“…We speculate that out-of-sequence thrusting or syn-orogenic extrusion of tectonic units preserving top-to-the E contractional structures at their base and W-verging extensional structures at their top, can be held responsible for the exhumation of HP metamorphic units to shallower crustal levels, as also proposed by Brogi and Giorgetti (2012), Molli et al (2018bMolli et al ( , 2000, Montomoli et al (2009), Storti (1995) for the Tuscan Metamorphic Units and Keller and Pialli (1990), Papeschi et al (2020), Pertusati et al (1993) and Ryan et al (2021) for the Elba Island. However, future geochronological work is needed to test that the compared structures are coeval.…”

“…Unit: Molli et al, 2000; some evidence for the Acquadolce Subunit, Elba Island: Ryan et al, 2021), whereas most of the preserved ductile structures are defined by greenschist facies retrograde assemblages, with the relic HP parageneses only preserved in microlithons (Monte Argentario: Theye et al, 1997;Elba Island: Bianco et al, 2019;Papeschi et al, 2020;Monti Pisani: Lo Pò & Braga, 2014).…”

“…Successively, these tectonic units were exhumed, stacked, and juxtaposed below their nonmetamorphic counterparts (Ligurian Units and Tuscan Nappe). In the NA, only few structures are directly related to HP parageneses (Monticiano‐Roccastrada Unit: Brogi & Giorgetti, 2012; Massa Unit: Molli et al., 2000; some evidence for the Acquadolce Subunit, Elba Island: Ryan et al., 2021), whereas most of the preserved ductile structures are defined by greenschist facies retrograde assemblages, with the relic HP parageneses only preserved in microlithons (Monte Argentario: Theye et al., 1997; Elba Island: Bianco et al., 2019; Papeschi et al., 2020; Monti Pisani: Lo Pò & Braga, 2014).…”

Interactions of plutons and detachments: a comparison of Aegean and Tyrrhenian granitoids

“…Other constant parameters include friction ϕ and cohesion C, which varies linearly with plastic strain in the range [0,1] from 30 to 20 • and from 20 to 2 MPa; the coefficients of thermal expansion and compressibility are set to 3 × 10 −5 K −1 and 10 −11 Pa −1 . (Salemink, 1985) and Naxos (Pe-Piper et al, 1997). Mixing/mingling processes between mafic mantle-derived melts and acid magmas produce composite batholiths (Poli and Tommasini, 1990) as illustrated by the case of the island of Elba magmatic complex shown for comparison (see Dini et al, 2002, for explanation).…”

“…The case of the Tuscan Archipelago is partly similar to the geothermal fields of Larderello and Monte Amiata developed above recent shallow plutons in a context of asymmetric extension with topto-the-east low-angle shear zones (Jolivet et al, 1998;Brogi et al, 2003;Rochira et al, 2018). The Monte Capanne and Porto Azzuro plutons on Elba are associated with hydrothermal activities and mineralization (Maineri et al, 2003;Rossetti and Tecce, 2008;Liotta et al, 2015) that make them good exhumed analogues of active geothermal fields, a situation that is found also in the Cyclades with the mineralizations observed on Mykonos or Serifos in the Cyclades (Salemink, 1985;St. Seymour et al, 2009;Menant et al, 2013;Tombros et al, 2015;Ducoux et al, 2016).…”