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Int J Earth Sci (Geol Rundsch) (2018) 107:1343–1355
DOI 10.1007/s00531-017-1539-9
ORIGINAL PAPER
Lateral extrusion of a thermally weakened pluton overburden
(Campiglia Marittima, Tuscany)
Simone Vezzoni
1
· Sergio Rocchi
1
· Andrea Dini
2
Received: 1 February 2017 / Accepted: 4 September 2017 / Published online: 3 October 2017
© Springer-Verlag GmbH Germany 2017
Keywords Extensional tectonics · Magmatic rocks ·
Skarn · Northern Apennines
Introduction
The mobility of magmas and hydrothermal fluids in the
upper crust plays a key role in geological processes such as
volcanic eruptions, ore deposition, and activation of geo-
thermal systems. The required country rock permeability is
commonly enhanced by tectonic activity, focusing magmas
and fluids in structural paths and traps. However, the active
contribution to tectonics by magma emplacement at a local
scale is still to be assessed in full. This is due, in part, to the
general lack of evidence for the pathways followed by mag-
mas and fluids once emplacement processes are over, so that
geometries and textures of igneous and hydrothermal bodies
represent the only witness to those pathways.
The late Miocene–Quaternary extensional setting of
southern Tuscany offers the possibility to investigate at dif-
ferent crustal levels the interplay between processes that led
to the generations of the Tuscan Magmatic Province (Serri
et al. 1993), active high-enthalpy geothermal fields (Lar-
derello–Travale and Monte Amiata: Batini et al. 2003), and
fossil hydrothermal systems (Dini et al. 2008a; Mazzarini
et al. 2011), as well as different types of ore deposits (Fe-
oxides, pyrite, base metals, and Sb–Hg ores; Tanelli 1983).
In detail, the study area of Campiglia Marittima (hereaf-
ter Campiglia) was affected by igneous activity during the
latest Miocene–early Pliocene, linked with generation of
metasomatic rocks and ore bodies exploited since Etruscan
times (Barberi et al. 1967; Da Mommio et al. 2010). Here,
detailed mapping and analysis of a cumulative 20 km of min-
ing tunnels, associated with deep boreholes data and geo-
physical interpretative maps, allowed us to reconstruct the
Abstract The ascent and emplacement of magmas in
the upper crust modify the local pre-existing thermal and
rheological settings. Such changes have important effects
in producing anomalous structures, mass extrusion, rock
fracturing, and in some conditions, hydrothermal miner-
alizations. In the Campiglia Marittima area, detailed field
mapping led to the reconstruction of a local deformation
history that overlaps, chronologically and spatially, with
regional extension. This local deformation was triggered at
the Miocene–Pliocene boundary by the intrusion of a mon-
zogranitic pluton beneath a carbonate sedimentary sequence.
The emplacement of the pluton produced a perturbation in
the rheological behaviour of the carbonate host rocks, pro-
ducing transient ductile conditions in the very shallow crust.
The carbonate rocks were thermally weakened and flowed
laterally, accumulating downslope of the pluton roof, mainly
toward the east. As the thermal anomaly was decaying, the
brittle–ductile boundary moved progressively back towards
the pluton, and large tension gash-shaped volumes of frac-
tured marble were generated. These fractured volumes were
exploited by rising hydrothermal fluids generating sigmoidal
skarn bodies and ore shoots. This work presents the Campi-
glia Marittima case study as a prime example of structural
interference between regional extensional structures and
local, lateral mass extrusion in a transient ductile rheologi-
cal regime triggered by pluton emplacement.
* Simone Vezzoni
vezzoni@dst.unipi.it
1
Dipartimento di Scienze della Terra, Università di Pisa, Via
Santa Maria, 53, Pisa, Italy
2
Consiglio Nazionale delle Ricerche, Istituto di Geoscienze e
Georisorse, Via Moruzzi, 1, Pisa, Italy
@Phil_Robichaud
@deepthiw
@JoseServera