Publication Date:
2021-06-15
Description:
The E-vergent Northern Apennines formed by Oligocene-Miocene convergence and
westward subduction of Adria beneath Europe. Extension ensued in the Mid-Late Miocene reflecting
lower plate roll-back and causing opening of the back-arc Northern Tyrrhenian Sea. Post-orogenic
extension is commonly advocated as the main driver of the exhumation of the belt's inner domain highpressure/
low-temperature (HP-LT) rock units. The Acquadolce Subunit of the Eastern Elba nappe stack
contains HP-LT rocks recording peak blueschist conditions of 1.5–1.8 GPa at 320°C–370°C loosely dated to
the Oligocene-Early Miocene. It is sandwiched by two Late Miocene, out-of-sequence top-to-the E thrusts
between Jurassic LP serpentinites on top and HT–LP contact metamorphosed marbles at its base. We
document widespread W-verging ductile asymmetries within the Acquadolce Subunit, which correspond
to top-to-the W extensional shearing for the nappe stack current orientation. This allowed for early
syn-orogenic exhumation from blueschist- to greenschist-facies conditions, wherein coeval W-directed
extension at the top of the exhuming units acted synchronously with E-directed thrusting at their base
causing exhumation by extrusion in an overall contractional setting. The basal, E-vergent thrusting is,
however, challenging to document as the wedge has since been reworked by Late Miocene, E-verging
compressive tectonics, contact metamorphism, and later extension, obliterating much of the evidence
supporting exhumation by extrusion during the early stages of wedge build-up. Syn-orogenic exhumation
by extrusion from deep structural levels within the orogenic wedge is a viable mechanism to account for
other exhumed HP-LT units in the inner part of the belt.
Description:
Published
Description:
e2020TC006348
Description:
1T. Struttura della Terra
Description:
JCR Journal
Keywords:
Syn-orogenic extrusion is proposed as a viable mechanism for the exhumation of HP-LT rock units of the Northern Apennines; • The Acquadolce Subunit of the Eastern Elba nappe stack was exhumed by upward extrusion within an actively shortening orogenic wedge; • Middle Miocene extension shaped the upper Northern Apennines orogenic wedge but did not contribute to the early exhumation of HP rocks.
;
04. Solid Earth
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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