Michael Lacroce
Field Camp Italy
Dr.Bice
6/9/14
The Tuscan Apennines
After flawlessly mapping the Umbria-Marche region the Jackson 5 traveled to the Tuscan Region
of the Northern Apennines to analysis the tectonic evolution of the Umbria Marche Apennines. The
Tuscany region has three tectonic “acts”. Act I starts with an extensional phase from late Triassic to early
Paleocene. Act II is a compressional phase in most of the Tertiary. In Act III compression stops and
extension occurs again which is the current tectonic phase the region experiences today. Our goal was
to observe the indications in the region and conjugate how these interpretations were made. The
Tuscany Apennine region shows the unique deformation that occurred during the compressional phase
of the Apennines tectonic evolution. In this region we can observe the main features of an orogenic belt
including thrust sheets, recumbent folds, a metamorphic complex, and the Liguride complex- which is a
large accretionary wedge. The region is a well studied area and contains very unique outcrops.
Act I began with the rifting of Pangea between Europe and Adria. Eurasia traveled North
attached to North America when Adria moved with Africa moving away from Eurasia creating the
Liguraide ocean. Oophiolites are remains of oceanic crust and are visible in the Tuscana Apeninnine
region at Stop 13. These oophiolites are pillow basalts which are remnants of the upper layer of the
Ligurde ocean crust. Pieces of the Liguaride ocean crust where scraped off once subduction occurs in the
Jurassic creating the Ligurade Accrectionary wedge. The Ligurade accrectionary wedge is a complex stew
of old Ligurade ocean crust and flysch created by the subduction that happened in the Jurassic, this
evidence of the extension lie within the oldest rocks of the Tuscan Nappe stratigraphy. The Clacare
Cavernoso is a limestone with voids and usually is composed of dolostones and evaporates located at
the base of the Tuscan Nappe sequence. Throughout the Alpine Apine region we see the Clacare
Cavernoso as low grade metamorphic limestone clasts, that are incased in large breccia. The Clacare
Cavernoso contains large evaporates formed around low to mid Triassic which indicated a long period of
subsiding of the Largurie ocean creating a dry arid environment for evaporation to occur. A long
subsiding period provides evidence of extension of this area draining the Liguride Ocean.
The formations that deposited in the Liguride ocean floor were the Calcare Massiccio Formation,
the Angulati, the Rosso Ammonitico, the Calcare Selcifero, the Diaspri, and the Maiolica formations.
Similar to the Massiccio seen in the Umbria Marche region the massive limestone was a carbonate
platform. As extension continued horst garben formations formed from normal faulting. Post Massiccio
deposition, the formations between Angulati and Maiolic where deposited on top of horst graben
formations during the Early Jurassic. The faulting left large breccia with limestone and breccia clast. In
order for breccia to form there most of been large amounts of deformation creating the angular clast we
saw in the river. This could only occur if these formations where exposed, possibly from the normal
faulting. The next formation to mention is the Scaglia Toscana which consist of turbindites in the lower
half with a variety of clast the older limestone formations. These turbidites also took part in forming
these large breccia. The limestone clast inside the breccia underwent low grade metamorphism once
the Tuscan Nappe started to undergo subduction once compression occurred in the region. The top of
the Scagila Toscana is capped by the Macigno flysh. The Macigno Flysh is a thick sequence of turbidites
and interbedded shales completing the Tuscan Nappe sequence. The Macigno was deposited late
Eocene and Oligocene marks the beginning of the compressional phase of the tectonic evolution.
About the late Eocene started the compressional phase (Act II) of the Northern part of the
Apeninnes. It started 70-80 Ma when Africa began to rotate northward towards Europe. The motion
change of Africa led to the subduction of the Adria ocean crust and the creation of the Liguride
accretionary wedge complex. The foredeep basin created by the Liguride wedge is where the Macigno
flysh deposited. The subduction caused turbidity currents flowing from the NE as shown in Plot 3. As the
the Adria crust was pulled under the Liguride accretionary wedge the Tuscan sequence detached from
the original crust in a process called under plating. This thrust sheet became the Tuscan Nappe and
moved east relative to the Adria plate. As the convergence of the Adria continued the flysch deposition
moved to the east creating the Cervarola formation. At this time the Tuscan Nappe was still being
underplated. The paleoflow of the Cervarola is more eastward and also contains sandstone turbidites
possibly created from the Alps. Eventually as subduction continued the Cervarola would become the last
formation to become under plated.
This general under plating process is key to the metamorphic Alpi Apuane complex. The under
plating sequence began with the Tuscan Nappe. Once the Tuscan Nappe thrusted over the original crust,
deformation and thrust faults continued to form. The sequence under the Tuscan Nappe is thought to
be the Alpi Apuane which experienced lots of pressure from the overlying Tuscan Nappe creating a low
grade metamorphism. As thrusting continued the Alpi Apuane thrust over the Cervarola uplifting the
Tuscan Nappe above it creating the metamorphic complex seen in our cross section. The low grade
metamorphism created turned the Jurassic limestone into marble. This marble resource has been
excavated since the Roman times and is still mined today. Below that the Alpi Apuane complex has
major deformation in the formations we saw on our way to the marble quarries. This deformation is
complex as we see folding and compaction from multiple directions as seen in Plot 2. This indicates large
amount of deformation from the trusting events.
After the complex compaction history at about 15 Ma, extensional tectonics returned to the
Tuscan Apennine regime. This produced normal faults creating the Garfagnana graben where we see the
Liguride complex at the bottom of the valley. Extension is still occurring in this region creating small
scale earthquakes and landslides in the region.
The Tuscan region of the Apennines holds a complex tectonic evolution. It is one of a kind
because the outcrops it holds shows the history of how it was formed whereas the Umbria Marches
region that we mapped last week had most of the formation process buried deep beneath the limestone
beds. There are still many holes in the tectonic evolution that only more studying can reveal. One major
question is why did the Tuscan Nappe not undergo any metamorphism. One answer could be that the
temperature gradient of the formations cooled the Tuscan Nappe at lower levels where the pressure
would cause metamorphism; where as the Alpi Apuane had the high temperature and pressure levels to
undergo the metamorphism. Only more studies can help us find the answers.