Mem. Soc. Ceol. Il.,
52 (1998), 469-478, 4 ff.
PALEOMAGNETIC CONSTRAINTS TO THE TECTONIC EVOLUTION
OF THE NORTHERN ITALIAN PENINSULA
MASSIMO MATTEI ("), FABIO SPERANZA ('d,), LEONARDO SAGNOTTI ('d'),
RENATO Fu ICIELLO (',) & CLAUDIO FACCEN A (i,)
ABSTRACT
Several paleomagnetic studies were performed in
the northern Italian peninsula since the mid 1970s,
when various research groups investigated the MesoCenozoic pelagic carbonatic sequences of the Apenninic chain. The first paleomagnetic results generally
showed western declinations which were interpreted
as due to a general counterclockwise
(CCW) rotation
of the whole Italian peninsula, a concept that had a
broad influence on nearly all the geodynamic models
proposed for the centraI Mediterranean.
At the same
time the paleomagnetic results obtained along the arc
showed larger CCW rotations in the northern part of
the arc than in its southern part, initiating a long-standing scientific debate about the oroclinal origin of the
Umbria-Marche Apennines. In the last few years our
group faced these two topics by means of new paleomagnetic investigations. We sampled 131 sites (about
1300 samples) in marine clay units deposited in the
Neogene foredeeps of the Apenninic chain and in
«neo-autochthonous»
sequences along the TuscanLatium extensional Tyrrhenian margino A characteristic remanent magnetization
(ChRM) was isolated in
101 sites which were used for the tectonic interpretation. Magnetic mineralogy analyses, positive fold and
reversal tests demonstrated the primary ori gin of the
ChRM. Paleomagnetic results show that the tectonic
evolution of the Umbria-Marche-Romagna
and Latium-Abruzzi regions was accompained, after the Messinian, by large differential rotations about vertical
axes. Extensional tectonics developed at the same time
along the Tuscan-Latium Tyrrhenian margin without
any rotation. The central-northern
Apenninic chain,
originally straight and oriented about N320°, assumed
its present arcuate shape throughout differential rotations connected to thrust sheets emplacement
and
strike-slip activity.
The null rotation of the Tuscan-Latium «neo-autuchthonous» basins demonstrates
that the opening of
the northern Tyrrhenian Sea was not accompained by
rotations of its eastern margin, thus implying a different tectonic evolution with respect to the southern Tyrrhenian Sea and the Liguro-Provençal basino
(*) Dipartimento di Scienze Geologiche, Università ROMA TRE, Largo S. Leonardo Murialdo 1,00146
Roma.
('''') Istituto Nazionale di Geofisica, Via di Vigna
Murata 605 - 00143, Roma.
KEy WORDS: Paleomagnetism,
Apenninic
Tyrrhenian
Sea,
chain, Neogene.
RIASSUNTO
L'Appennino settentrionale è stato oggetto, a partire dagli anni settanta, di numerosi studi paleomagnetici che hanno analizzato le successioni carbonatiche meso-cenozoiche diffusamente affioranti nell'area.
I primi risultati ottenuti nell'area umbro-marchigiana
mostrarono
declinazioni paleomagnetiche
nord-occidentali, di maggiore entità nei settori settentrionali rispetto a quelli meridionali dell'arco appenninico. Questi dati vennero largamente utilizzati a conforto della
postulata rotazione antioraria della penisola italiana e
furono l'oggetto di un'ampia discussione sull'origine
oroclinalica dell'arco umbro-marchigiano.
Negli ultimi
anni il nostro gruppo di ricerca si è occupato dello studio di queste rotazioni pianificando una nuova, estesa
campagna paleomagnetica. Sono stati campionati 131
si ti nelle unità argillose neogeniche affioranti nei settori esterni della catena e nelle unità post-orogene del
margine estensionale tosco-laziale. In 101 siti è stata
isolata una magnetizzazione
rimanente caratteristica
di origine primaria. I risultati ottenuti mostrano che
rotazioni di segno ed ampiezza differenti hanno condizionato l'evoluzione tettonica post-messiniana
dell'arco umbro-marchigiano-romagnolo
e della piattaforma laziale-abbruzzese,
mentre il margine tirrenico
tosco-Iaziale non ha subito alcuna rotazione a partire
almeno dal Messiniano. In particolare la catena appenninica centro-settentrionale
si è evoluta a partire
da una struttura rettilinea ad andamento circa N320°.
La progressiva rotazione delle strutture fino alloro assetto attuale è da imputarsi all'attività di fronti di accavallamento e, nell'Appennino centrale, ad importanti discontinuità trascorrenti. Durante lo stesso lasso di
tempo il margine tirrenico, interessato esclusivamente
da tettonica estensionale, non è stato soggetto ad alcuna rotazione. Ciò implica che il meccanismo di apertura del bacino tirrenico settentrionale
è profondamente differente da quello del TilTeno meridionale e
del bacino ligure-provenza le.
TERMINI CHIAVE: Paleomagnetismo,
no, Appennino,
Neogene.
Mar Tirre-
M. MATTEI ET ALli
470
INTRODUCTION
These data were first interpreted as the
result of an oroclinal evolution of the northern Apenninic arc (CHAN ELL et alii, 1978;
ELDREDGEet alii, 1985) and then attributed to
a complex deformative mechanism that involved pre-folding rotations of the sedimentary
units (HIRT & LOWRIE,1988). In any case the
paleomagnetic data demonstrated that the
northern sector of the arc rotated CCW more
than the southern part, even if they did not
«strictly» (i.e. by applying rigorous statistical
tests) prove definitively the oroclinal origin of
the arco
In order to better constrain the tectonic
evolution of the northern Italian peninsula we
carried out, in the last few years, new paleomagnetic studies. We sampled sedimentary
sequences coeval to the main tectonic events
(opening of the Tyrrhenian Sea and building
of the Apenninic chain), and distributed over
different structural provinces. The aim was to
distinguish the rotations related to the opening of the Tyrrhenian Sea from those due to
the deformation of the Apenninic chain. 131
sites (more than 1300 samples) were collected
in Neogene and Quaternary sedimentary
sequences located throughout the TuscanLatium Tyrrhenian margin and the foredeep
basins in northern and centraI Apennines.
In this paper we discuss the tectonic evolution of the northern Italian peninsula, integrating our paleomagnetic results with structural,
stratigraphical and geophysical data. A comparison between the tectonic evolution of the
northern Tyrrhenian Sea wi th respect to the
Liguro- Provençal basin will be also discussed.
The northern Italian peninsula was intensively paleomagnetically investigated since the
mid 1970s, when different group of reserchears studied the Meso-Cenozoic sediments
cropping out in the Umbria-Marche Apennines. The first paleomagnetic results were
published by LOWRIE& ALVAREZ(1974), concerning the upper Cretaceous Scaglia Formation in the Umbria-Marche region. The western paleomagnetic declinations reported in
this first study were later also recognized both
on the Apulian foreland (CHANNELL,1977;
MARTO & VELJOVIC, 1983; VANDENBERG,
1983) and elsewhere in the Apenninic chain
(LOWRIE& ALVAREZ,1975; CHANNELL& TARLI G, 1975; CHAN ELL et alii, 1978; VANDENBERGet alii, 1978; HII~.T& LOWRIE,1986). The
results from Umbria, were originally interpreted by LOWRIE & ALVAREZ(1974, 1975),
who assumed the studied sequences as
«autochthonous» and representative of the
whole Italian peninsula, in terrns of a 30°-40°
Cretaceous and 25° post-Eocene counterclockwise (CCW) rotation with respect to Europe,
and then by VANDENBERG
et alii (1978) as the
result of a post-Early Eocene 25° CCW rotation of the peninsula with respect to Africa. On
the other hand, CHANNELL& TARLING(1975)
and CHAN ELL et alii (1978) interpreted the
paleomagnetic results from Umbria-Marche
region as due to rotations of the sedimentary
cover, linked with the emplacement of the
Apenninic thrusts. More recently CHANNELL
(1992) showed that the whole set of paleomagnetic data does not imply a Tertiary CCW rotation of the whole Italian peninsula.
In spite of this debate about the geodyGEOLOGICAL SETTING
AND PALEOMAGNETIC SAMPLING
namic significance of the paleomagnetic data,
the idea of the CCW rotation of the Italian
The northern Italian peninsula is formed
peninsula became a common assumption in
the tectonic reconstructions of the centraI by several geodynamic provinces with distincMediterranean region, and was considered
tive geological, tectonic, and geophysical characters. The Apenninic chain is mainly comthe cause for the opening of the Tyrrhenian
Sea, as the CCW rotation of the Corsica-Sarposed of sedimentary sequences arranged in
arcuate thrust sheets, verging toward the Adridinia block was for the Ligure-Provençal
basin (CAREY,1938; BOCCALETTI
et alii, 1974;
atic foreland (fig. 1). The regional metamorSARTORI,1990; DOGLIONI,1991; CASTELLARIN phic basement crops out only in the western
et alii, 1992).
part of the chain, whereas the sedimentary
cover, which includes carbonatic platform to
Paleomagnetic results from the UmbriaMarche region showed variations of the paleo- pelagic Meso-Cenozoic sedimentary sequenmagnetic declinations along the arc, the more ces, is widespread in the axial sector of the
westerly declination being reported from its chain. Syn-orogenic siliciclastic units, deposited in foredeep basins, constitute the last epinorthern part.
471
PALEOMAGNETIC CONSTRAINTS TO THE TECTONIC EVOLUTION
45"-
o
100 km
I
i
I
44"-
,()
43'L
f++
:
~+ +.1
Volcllnic and p/utonie
unirs
Extensional sedimentar)) basi"s
lhe Tyrrhenian
margin
_
Plioce[le./ored!!ep
ApelllllfllC
cltaln
l:-:-:-:·:j
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ellain
~:-,;.:-;l "Epi-Liguriall"
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basins
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oi file
oJ lITe
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platforms
Umbria-Marche
Uflit.~'
EEEIJ Cervaro/a units
E3
Fig.
TUSCQII
units
~
Ligurian units
Il Il Il Il Il
Basemell!
unirs
•
~
Sampling
sites
Main trh"slFonlS
1 - Schematic map of the central-northern Italian peninsula and location of the sampling sites.
extensional regime developed along the
Tuscan-Latium Tyrrhenian margin after the
Late Miocene (ELTER et alii, 1975). This extensional phase was accompanied by the formation of large sedimentary basins, bounded by
normal faults, whose orientation changes from
N-S in the eastern sector to NW-SE in the
472
M. MATTE! ET ALII
western sector. The sedimentary extensional
basins are filled by late Miocene-Pleistocene
continental, brackish and marine sequences of
the «neo-autochthonous» sedimentary cycle.
These sediments unconformably cover the
compressional
Apenninic structures.
The
extensional tectonics was also accompanied by
diffuse magmatic activity. Crustal stretching
migrated progressively eastward, following the
Apenninic compressional episodes, from the
Tyrrhenian coast to the axis of the Apennines
chain, where it is active today.
In the centraI Apennines we sampled 39
sites in Middle Miocene to Lower Pliocene
marls and clays, mainly deposited in the
migrating Apennines foredeep, distributed
over the Sabina, Latium-Abruzzi and Marsica
regions (MATTEIet alii, 1995). In the northern
Apennines we sampled 32 sites mainly in Messinian sediments at the external front of the
Umbria-Marche-Romagna arc, from the Gran
Sasso chain to the Sillaro line (SPERANZAet
alii, 1997). In the Tuscan-Latium Tyrrhenian
margin we sampled 60 sites in Messinian-Pleistocene clay-rich sediments from the Volterra,
Val di Fine, Orcia, Siena-Radicofani, Mignone,
Tiber and Ardea basins (SAGNOTTIet alii,
1994; MATTEI et alii, 1996a; MATTEI et alii,
1996b). In the following sections we will briefly overwiew the paleomagnetic results from
the Apenninic chain and from the Tyrrhenian
margin and discuss their implications for the
tectonic evolution of northern Italy.
PALEOMAGNETIC RESULTS
APENNINICCHAIN
In 45 out of 71 sites a Characteristic Remanent Magnetization (ChRM) was isolated.
This component is interpreted of primary origin, as suggested by positive fold and reversal
tests. Detailed description
of laboratory
experiments, magnetic mineralogy and paleomagnetic data can be found in MATTEIet alii
(1995) and SPERANZAet alii (1997). Most of
the data show a paleomagnetic inclination
significantly shallower than the present-day
one. Such inclination flattening is not correlated to the geographic or stratigraphic distribution of the sampling sites and clearly
reflects compaction-related
effects on the
studied sediments. We exclude that the inclination scatter results from tectonic processes,
and we discuss paleomagnetic results only in
terms of paleodeclination values. Because of
the absence of a reference pole for the Adriatic foreland and the Italian peninsula since
the Late Miocene, we interpret paleomagnetic
declinations in terms of vertical axes local tectonic rotations. In fig. 2 we show the paleomagnetic directions obtained in the Apenninic
chain. From a generaI point of view it is clear
that the northern Apennines underwent differential clockwise (CW) and CCW rotations
which depict a complex deformative history.
Distinct rotational domains can be observed,
which are separated by major tectonic elements or, such as in the Umbria-Marche
region, represent different segments of arcuate structures. In the centraI Apennines three
different domains were recognized (MATTEIet
alii, 1995): the Sabina region, that underwent
a post middle Miocene CW rotation of about
16°; the Latium-Abruzzi platform with a post
Messinian CW rotation of about 28° and the
western border of the Latium-Abruzzi platform (Eastern Marsica) with post Messinian
CW rotations of variable amplitude.
Along the Umbria-Marche-Romagna
arc
different paleomagnetic rotations were found
(fig. 2). In this region we took into account
also the paleomagnetic results obtained by
DELAPIERRE et alii (1992) and LANCI &
WEZEL(1995). North of the Gran Sasso thrust
front paleomagnetic declinations are about NS, suggesting no rotation of the Acquasanta
and Montagna dei Fiori structures since the
Messinian. Toward the north, CW rotations of
about 10°-20° were found in the Messinian
Laga Formation. To the north of the Cingoli
anticline different amounts of CCW rotations
were recorded mainly in the Upper Messinian
Colombacci Formation. The sites between the
Cingoli anticline and the Val Marecchia unit
show about 20° CCW rotation, whereas the
sites to the north of the Val Marecchia unit
show CCW rotations up to 60°. CCW rotations
of about 20° were measured further north up
to the Sillaro tectonic line. The whole set of
data from the Central-Northern Apennines
shows that the paleomagnetic declinations
and the structural directions (fold axes and
thrust fronts) are significantly correlated,
both at regional and at local scale. In particular, the structures oriented N-S to NNW-SSE
(such as those in the Sabina, Marsica and at
the southern Sibillini front) are generally
associated to CW rotations, whereas for the
PALEOMAGNETIC
CONSTRAINTS
TO THE
TECTONIC
EVOLUTION
473
Paleomagnetic declinations from the
Tuscan-Latium Tyrrhenian margin
45~
Paleomagnetic declinatiol1s from the
Apenninic chain
44~
{)
43~
,+. ::
:1
Va/cmlic
and plutOllic
UflilS
Il
L-....J
Extellsio1lal
sedimemary
c!le Tyrrheniall
margin
_
Pliocefle.fored.eep
ApenllllJlC
challl
I:-:':-:-:~Mess;,~;a.'l
fore.deep
. . ..
Apelllll1l1C
challl
B
W
B
Umbria·Marche
~
Liguria"
unils
Basemellt
wlits
~:-;':-j.l "Epi·Ligurian"
EJ
vv vv
Carbollatic
Cervaro/a
basins 0/
basifls
hasills
of file
of che
units
platforms
un;/s
ullits
TusCQIl uflits
~
Maill trllUslfrollls
Fig. 2 - Ti!t corrected
pa!eomagnetic declinations (ali transferred
Apennines and Tuscan-Latium Tyrrhenian margino
structures oriented NW-SE (such as LatiumAbruzzi platform and northern Umbria-Marche-Romagna arc) the paleomagnetic data
indicate consistent CCW rotations. Local
structures also support this generaI pattern.
The Roveto Valley, for example, is formed by
NW-SE oriented structures bounded by thrust
to norma! polarity) along the central-northern
and left-Iateral strike-slip faults (MONTONE&
SALVINI,1993). This trend is almost constant
along the valley, except nearby the Canistro
structure, where the fold axes turn toward a
N-S orientation. Paleomagnetic data show a
generaI post-Messinian CCW rotation along
the Roveto Valley except in the Canistro struc-
M. MATTEl ET ALll
474
80
60
Y=7.3+1.2X
R=O.814
40CI)
Z
20
O
•..• 0~
b -20~
-40
-60-80
-60
20
40
60
STRUCTURAL DIRECTIONS
Fig. 3 - Declination
deviations relative to fold axis deviations. The Y axis represents the measured paleomagnetic declination, the X axis represents the deviation of
the fold axis respect to a reference direction 315°.
ture, where CW rotations were observed, demonstrating that the change of structural directions is due to differential rotations. This
behavior was also observed in the Romagna
region, where the geometry of minor arcuate
structures, separated by major tectonic boundaries (e.g. Forlì line) appears related to differential vertical axis rotations.
In order to test statisticalIy the relationships between the measured paleomagnetic
rotations and the structural trends of the
compressional structures, we performed a
regression analysis between the paleomagnetic declinations and the fold axis orientations. Fig. 3 shows that, except for the Acquasanta-Montagna dei Fiori structures, the data
are positively correlated (correlation coefficient R=0,814), thus implying that the present-day orientation of the compressional
structures is totalIy due to differential rotations after Late Miocene-Early Pliocene. The
statistical significance of the inferred correlation was proved (at a 99% significance level)
performing a t test (MATTEIet alii, 1995; SPERANZAet alii, 1997).
TUSCAN-LATIUM
TYRRHENIANMARGIN
In the Tuscan-Latium Tyrrhenian margin
39 out of 60 sites provided reliable paleomag-
netic results (fig. 2). Positive fold and reversal
tests indicate the primary origin of the isolated ChRM. Detailed description of laboratory experiments, magnetic mineralogy and
paleomagnetic data can be found in SAGNOTTI
et alii (1994); MATTEIet ali i (1996a); MATTEI
et alii (1996b).
The paleomagnetic results are consistent
throughout the whole region and within the
different sampled basins. In the Val di Fine
Basin the mean direction calculated for the
Messinian sites is D=I.4°; 1=54.9°; k=93;
a9s=9.6°. In the Volterra Basin 13 sites in
Messinian-Lower Pliocene sequences give a
mean direction defined by: D=350.2°; 1=58.0°;
k=58.4; a9s=5.5°. In the Siena-Radicofani
Basin 12 sites in Lower Pliocene sediments
define a mean paleomagnetic
direction
D=357.3°; 1=56.9°; k=76.7; a9s=3. 1°. In the
Latium Tyrrhenian margin 12 sites sampled
in Upper Pliocene-Lower Pleistocene sequences, provide a mean paleomagnetic direction:
D=358.00; 1=55.2°; k=115.l; a9s=4.l°.
The overall mean direction calculated far
alI the studi ed Tuscan-Latium extensional
basins is D=357.5"; 1=56.5"; k=84.3; a9s=2.5°,
which indicates that the northern Tyrrhenian
margin as a whole did not rotate since the
Messinian.
DISCUSSION
The new paleomagnetic data from the
northern Italian peninsula concur with other
geological and geophysical data to outline distinct geodynamic provinces, which underwent
differential rotations during Neogene and
Quaternary times. During such time interval
the Apenninic chain underwent large and
complex rotations while, at the same time, the
northern Tyrrhenian margin did not rotate.
The bearings of such data far the geological
and tectonic reconstructions of the northern
Italian peninsula and the Tyrrhenian Sea will
be discussed in the next sections.
NEOGENETECTONICEVOLUTIONOF THE CENTRAL-NORTHERN
APENNINICCHAIN
The paleomagnetic data demonstrate that
rotation about vertical axis is a main deformative mechanism characterizing the PliocenePleistocene thrust sheets emplacement and
strike-slip activity in the central-northern
PALEOMAGNETIC
CONSTRAINTS
Apennines. If we rotate back the present-day
fold axes for the measured paleomagnetic
rotations they became constantly oriented
around N320°, indicating that during the Messinian, the chain-foredeep system was almost
rectilinear (fig. 4). Progressive rotations during the thrusts propagation produced the
complex geometry of the compressional structures and the present-day arcuate shape of the
Apenninic chain. Most of the rotations should
have occurred during the emplacement of the
major out-of-sequence thrust sheets, such as
the Gran Sasso front and the Olevano-Antrodoco line. Rotations associated to thrust activity along these structures resulted in the present-day non coaxiality of the chain-foredeep
system and allowed single thrust units to
overlie foredeep basins of different ages
(CIPOLLARI& COSENTINO,1992; MATTEI et
alii, 1995, Bg. 14).
TO THE
TECTONIC
475
EVOLUTION
The detailed knowledge of the sense and
amount of rotations in the Apennines allows
to define precisely the thrust sheets trajectory
and can strongly support a correct balancing
of cross-sections. In the northern Apenninic
chain, since BALLY et alii (1986), a large number of balanced cross-sections has been proposed, mainly considering surface geology
and interpretation of seismic data. The thrust
sheets trajectories, reconstructed
restoring
balanced cross section (e.g. BALLY et alii,
1986; ME ICHETTI,1996), generally show larger CCW rotations in the southern part of the
Umbria-Marche arc, which are opposi te to the
evidences from the paleomagnetic data (see
also CHANNELLet alii, 1978). It seems clear
that an integrated approach to the balancing
of cross-sections using together structural,
seismic and paleomagnetic data allows to
define better the thrust sheets geometry at
Messinian (-6.5-
..
:-'l: :- :- .
".'::::.;----r::;
l:. :..:...:...:.....1
Rifted area filled
by "'neoautochthonous'
continental
deposits.
[]j]]]]J
Cervarola and Tuscan nappes, internai units.
=
Internai Umbria-Marche-Romagna domain.
1=
= 1
~
External Umbria-Marche-Romagna
~
Lazio-Abruzzi platform.
marine and
domain.
Flysch deposits
~
Faults:
Fig. 4 - Schematic
model of the tectonic evolution of the northern
External frent of the Apenninic chain
~
thrust
I
italian peninsula.
strike-slip
\
norma I
476
M. MATTEI
depth and also contributes to the estimatation
of the exact amounts of shortening along the
different sectors of the chain.
OPE
l
G OF THE TYRRHENIANSEA
Different mechanisms have been proposed to explain the origin of the Tyrrhenian
Sea basin (see SERRIet alii, 1991 for a review).
In a recent paper FACCE A et alii (1996)
explored, by means of analogue lithospheric
model, the possible contributions of three of
these different proposed mechanisms: the
indentation of the African plate, the consumption of the Adria-Ionian plate and the collapse
of a thickened Alpine crust. Other mechanisms, such as astenospheric (horizontal or
vertical) mantle flow, have not been experimentally modelled. Despite the over-semplification of our models, they simulate the extensional process in the Tyrrhenian Sea with the
combination of far field-stress, generated by
plate interactions and/or subduction, with
near field-stress, mainly linked to body forces
(FLEITOUT& FROIDEVAUX,1982; MOLNAR&
LYON-CAEN,1988) stored in the crust previously affected by the Alpine-Apenninic thickening evento
Our paleomagnetic data show that, at
least since the Messinian, the northern Tyrrhenian Sea opened without any rotation of
the Tuscan-Latium margin, indicating that
the change in the structural trend within the
extensional northern Tyrrhenian basin (from
N-S in the Corsica basin to NW-SE in Tuscany) does not result from passive rotation of
the already formed extensional structures (fig.
4). On the base of our analogue models and
numerical simulation (see for a review BASSI,
1995), we suggest that at regional scale location, geometry and mechanics of extensional
tectonics is connected to the crustal heritage
of a thickened Alpine-Apenninic chain. At
smaller scale, a similar process can be envisaged in many sectors of the Appenninic chain,
where normal faults follow the trend of the
main compressional structures and its arcuate
geometry under the influence of the pre-existing topography and crustal weakness zone
(i.e. Gran Sasso Range, D'AGOSTINOet alii,
1997).
We underline that a non rotating opening
mechanism is not common to all the extensional basins within the Mediterranean Sea.
As a matter of fact, the adjacent Liguro-Pro-
ET ALIl
vençal Basin opened during the CCW rotation
of the Corsica-Sardinia block (VIGLIOTTl&
KENT, 1990). This difference, which implies a
distinct geometry and evolution of the sedimentary deposits (FUNICIELLOet alii, 1997),
can be due to a difference in the pre-rift rheology of the area. In the Corsica-Sardinia
block rifting acted on a Hercynian «norma!»
crust, whereas in the Tyrrhenian Sea the
extensional tectonics affected a thickened and
thermally relaxed unstable Alpine crust.
ROTATlO OF THE ITALIA PE I SULA
The hypothesis of a CCW rotation of the
Italian peninsula was originally proposed by
LOWRIE& ALVAREZ(1974) on the basis of the
first paleomagnetic results obtained from the
Upper Cretaceous-Lower Tertiary sedi me ntary sequences of the Umbria-Marche region,
considered as autochthonous and representative of the entire Italian peninsula. Even if
other paleomagnetic studies (e.g. CHANNELL
et alii, 1978; CHANNELL,1992) demonstrated
the existence of different rotations throughout
the Italian peninsula, this mechanism is stili
largely used to explain the tectonic evolution
of the Centrai Mediterranean region. The new
paleomagnetic data demonstrate that, at least
for the Neogene and Quaternary periods, the
concept of an «Eulerian» CCW rotation of the
Italian peninsula, considered as a unique,
rigid block, is properly a non sense. We show
that not only the major tectonic domains, but
also the minor adjacent structures, underwent
different sense and amount of rotations during
their tectonic evolution. Therefore reconstructions which derive the originai orientation of
Meso-Cenozoic faults or paleogeographic
domains on the base of a generai «CCW rotation of the Italian peninsula» (e.g. TAVARNELLI, 1996) should be avoided, or, in case,
should use precise and detailed paleomagnetic data obtained in the examined structures. Moreover, it should be reminded that
the paleomagnetic
data from Mesozoic
sequences may represent the summation of
different tectonic rotations (e.g. movements of
«microplates» in the Mediterranean and localized deformations associated with the orogenic building of the Apenninic chain). Even
if only the Neogene and Quaternary sequences are concerned, we showed that the paleomagnetic data point out a complex deformation pattern that prevents the extrapolation of
477
PALEOMAGNETIC CONSTRAINTS TO THE TECTONIC EVOLUTION
the vertical axis rotations found in the Apenninic chain or in the northern Tyrrhenian
region to the adjacent geologic provinces (Le.
the Adriatic foreland). Paleomagnetic and
structural evidences clearly show a differrent
behaviour of the Adriatic foreland with
respect to the Apenninic chain. Otherwise
VAN DER Voo (1993) and CHANNELL(1996)
recently reviewed the available paleomagnetic
data from Adria, suggesting no relative rotation of this region respect to Africa during
Cenozoic. Infact they demonstrated that the
Cretaceous paleomagnetic poles obtained from
Istria, Gargano Apulia, Istria and Southern
Alps, are not significantly different from those
expected from the coeval African reference
poles, whereas paleomagnetic directions from
northern Umbria (Bosso/Sentino/Burano river
valleys) are rotated CCW with respect to
Africa.
basins. In our opinion geometry and orientation of extensional tectonics is influenced by
the preexisting rheology and topography and,
as a result, normal faults passively follow the
arcuate shape of the Apenninic chain.
Manoscritto pervenuto il 28 gennaio 1997.
Testo approvato per la stampa il 2 luglio 1997.
Ultime bozze restituite 1'11 novembre 1997.
REFERENCES
BALLY A.W., BURBI L., COOPER C.
&
GHELARDO
I R.
(1986) - Balanced sections and seismic reflection
profìles across the Cel1tral Apennines. Mem. Soc.
Geol. Ita!., 35, 257-310.
BASSI G. (1995) - Relative importance of strain rate and
rheology for the mode of col1tinental extension.
Geoph. Journ. Intern., 122, 195-210.
BOCCALETTI M., GUAZZONE G. & MA NETTI P. (1974) Evoluzione paleogeografìca e geodinamica del Mediterraneo: bacini marginali. Mem. Soc. Geo!. Ita!.,
13(2), 18-21.
CAREY S. W. (1938) - Tectonic evolution of New Guinea
and Melanesia, PHD thesis, University or Sidney.
CASTELLARlN A., COLACICCHI R. & PRATURLO A. (1978)
- Fasi distensive trascorrenze e sovrascorrimenti
lungo la «linea Ancona-Anzio» dal Lias medio al
Pliocene. Geologica Romana, 17, 161-189.
CHAN ELL J.E.T. (1977) - Paleomagnetism of limestones
from the Gargano peninsula (ltaly), and the implications or these data. Geophys. J.R. Astron. Soc.,
51,605-616.
CHANNELL, J.E.T., LOWRIE W., MEDIZZA F. & ALVAREZ
W. (1978) - Paleomagnetism and tectonics in
Umbria, 1taly. Earth Piane t. Sci. Lett., 39, 199-210.
CIPOLLARl P. & COSENTINO D. (1992) - Analisi biostratigrafìca dei depositi terrigeni a ridosso della linea
Olevano-Antrodoco.
Studi
Geologici
Camerti,
199112,143-150.
i
TRE UPPER NEOGENE TECTONIC EVOLUTION
OF TRE NORTRERN-CENTRAL
ITALIAN PENINSULA
In fig. 4 we present a tentati ve scheme of
the tectonic evolution of the northern Italian
peninsula as deduced by paleomagnetic, structuraI and strathigraphic data. In this mode!,
the internaI or external position of the different structural units is based on the age of the
foredeep deposits, which are assumed progressively younger toward the Adriatic Sea
(PATACCAet alii, 1990; CIPOLLARI& COSENTI o, 1992), whereas the average orientation
of the external front of the chain during the
Messinian is obtained restoring the different
structures by means of the measured pale 0magneti c rotations. The age of the tectonic
rotations is assumed to be the same of the
main tectonic structures which separate the
different rotational domains (Gran Sasso
front, Olevano-Antrodoco line; Sabina fault,
Sibillini thrust). During the Pliocene the chain
progressively evolved from a rectilinear bel t
toward the present-day arcuate shape. Rotations are connected to thrust activity, mainly
to out-of sequence thrust, and enhanced by
strike-slip faulting. During the rotations of the
Apenninic structures, the extensional Tyrrhenian margin did no rotate. The changing in
orientation of the Neogene extensional basin
does not result from passive rotations which
affected the already formed sedimentary
D'AGOSTI o
., CHAMOT ROOKE ., FUNIClELLO R.,
JOLIVET L & SPERA ZA F.. The role or pre-existing
thrust raulis and topography on the styles or extension
in the Gran Sasso range (Centrai Italy). Submitted.
DELA PIERRE F., GHISETTI F., LANZA R.
&
VEZZANI L.
(1992) - Paleomagnetic and structural evidence or
Neogene tectonic rotation or the Gran Sasso range
(Centrai Apennines, Italy). Tectonophysics,
215,
335-348.
DOGLIONI C. (1991) - A proposal ror the kinematic modelling or W-dipping subduction. Possible applications to the Tyrrhenian-Apennines
system. Terra
Nova, 3, 423-434.
ELDREDGE
S.,
BACHTADSE V.
&
VA
DER VOO R.
(1985) - Paleomagnetism and the orocline hypothesis. Tectonophysics, 119, 153-179.
ELTER P., GIGLlA G., TONGJORGI M.
&
TREVI SAN L.
(1975) - Tensional and compressional areas in
recent (Tortonian to Present) evolution or north
Apennines. Boll. Geofis. Teor. Appl., 17, 3-18.
478
M. MATTEI ET ALII
FACCENNA c., DAVV P., BRUN J.P., FUNICIELLO R.,
GIARDINI D., MATTEI M. & NALPAs T. (1996) - The
dynamics
approach
of back-arc extension: a laboratory
to the opening of the Tyrrhenian Sea.
Geoph. Journ. Int., 126, 781-795.
FUNICIELLO R., MATTEI M., SPERANZA F. & FACCENNA
C. (1997) - La geodinamica del sistema TirrenoAppennino. Le Scienze, 343, 44-53.
FLETOUT L. & FROIDEVAUX C. (1982) - Tectonics and
topography for a lithosphere containg density heteregeneties. Tectonics,
1, 21-56.
HIRT A. & LOWRIE W. (1988) - Paleomagnetism of the
Umbrian-Marches orogenic belt. Tectonophysics,
146,91-103.
JOUVET L., DUBOTS R, FOURNIER M., GOFFE B., MICHARD A. & JOURDAN C. (1990) - Ductile extension
in Alpine Corsica., Geology, 18, 1007-1010.
LANCI L. & WEZEL C.F. (1995) - Rotazioni tettoniche di
età Messiniana nell'Appennino marchigiano (abs.),
in Tettonica
Attiva e Geodinamica
del Sistema
Tirreno-Appennino,
LOWRlE W.
&
LOWRIE W.
&
330-332,
Camerino.
ALVAREZ W. (1974) - Rotation
peninsula. Nature, 251, 285-288.
ALVAREZ W. (1975)
dence for rotation
Geophys.
MARTON
E.
Res.,
&
of the
of ltalian
(1983)
results from the Istria peninsula
tonophysics,
91, 73-87.
MATTEl M., FUNlClELLO R.
- Paleomagnetic
(Yugoslavia). Tec-
& KrSSEL
C. (1995)
- Paleo-
magnetic and structural evidence for Neogene block
rotations in the Centrai Apennines
(Italy). J.
Geophys.
Res.,
100,
17.863-17.883.
MATTEI M., FUNICIELLO R.
&
& SALVINI F. (1991) - Evidences of NW-SE
Late Miocene strike-slip tectonics in Centrai Apennines near Tagliacozzo, Abruzzi. Boll. Soc. Geol.
MONTONE P.
It., 110,617-619.
R & SCANDONE P. (1990) - Tyrrhenian basin and apenninic arcs: Kinematic relations since late Tortonian times. Mem. Soc. Geol.
PATACCA, E., SARTORI
Ital.,
45, 425-451.
& SCANDONE P. (1987) - Segmentation and configuration of subducted lithosphere in ltaly: An important control on thrust-belt
and foredeep-basin evolution. Geology, 15,714-717.
SAGNOTTI L., MATTEl M., FUNICIELLO R. & FACCENNA
C. (1994) - Paleomagnetic evidence for no tectonic
rotation of the Centrai !taly Tyrrhenian ma l'gin since
upper Pliocene. Geophys. Res. Lett., 21, 481-484.
SARTORI R. (1990) - The main results of ODP leg 107 in
the frame of Neogene to Recent geology of Perityrrhenian areas. Proc. Ocean Drill. Program
Sci.
ROYDEN L., PATACCA E.
Results,
- Paleomagnetic eviItalian peninsula. J.
80, 1579-1592.
VELJOVIC D.
tal deformation,
Clark S.P., Burchfield
B.C. and
Suppe J. eds., Geol. Soc. Am., special papers, 218,
179-208.
KrSSEL C. (1995)
- No
tectonic rotation of the Tuscan Tyn-henian margin
(Italy) since Late Messinian. Journ. Geoph. Res.,
101, 2835-2845.
MATTEI M., KTSSEL c., SAGNOTTT L., FUNICTELLO R &
FACCENNA C. (1996) - Lack of Upper Miocene to
Present rotation in the Northern Tyrrhenian margin
(!taly): a constraint on geodynamic evolution. In
Morris A. & Tarling D. (eds.) Paleomagnetism
and
107,715-730.
SERRI G., INNOCENTI F., MANETTI P., TONARINl S. &
FERRARA G. (1991) - Il magmatismo
neogenico-
quaternario dell'area tosco-Iaziale-umbra: Implicazioni sui modelli di evoluzione geodinamica dell'Appennino settentrionale. Studi Geol. Camerti,
1991(1),429-463.
& MATTE I M. (1997) - Tectonics of the Umbria-Marche-Romagna Arc (centrai
northem Apennines, ltaly): New paleomagnetic
constraints. J. Geophys. Res., 102, 3153-3166.
TAVERNELU E. (1996) - Tethyan heritage in the development of the Neogene Umbria-Marche fold-andthrust belt, !taly: a 3D approach. Terra Nova, 8,
SPERANZA F., SAGNOTTI L.
470-478.
VANDENBERG J., KLOOTWlJK C.T. & WONDERS A.A.H.
(1978) - Late Mesozoic and Cenozoic movements of
the ltalian peninsula: Further paleomagnetic data
from the Umbrian sequence. Geol. Soc. Am. Bull.,
89, 133-150.
- Reappraisal of paleomagnetic
data from Gargano (South ltaly). Tectonophysics,
Tectonics
of the Mediterranean
Region,
Geological Society Special Pubblication,
105, 141-146.
MENlCHETTl M. (1996) - Analisi strutturale ed evoluzi-
VANDENBERG J. (1983)
one cinematica dell'Appennino umbro-marchigiano
attraverso la costruzione di sezioni geologiche bilanciate. In «Presentazione
dei risultati
del profilo
VAN DER VOO R. (1993)
sismico
VTGUOTTI L
CROP
03» Roma
7-9 Novembre,
MOLNAR P. & LVON CAEN H. (1988)
P. 67.
- Some simple
physical aspects of the support, structure and evolution of mountain belts. In: Process of continen-
98, 29-41.
- Paleomagnetism of the Atlantic, Tethys and lapetus Oceans. Cambridge
Univer-
sity Press,
Cambridge,
& KENT
UK.
D.Y. (1990) - Paleomagnetic results
of Tertiary sediments from Corsica; evidence of
Post-Eocene rotation. Phys. Earth and PIan. Int.,
62, 97-108.