Extensional tectonics on Sardinia (Italy): insights into the arc–back-arc transitional regime

Extensional tectonics on Sardinia (Italy): insights into

the arc–back-arc transitional regime

Claudio Faccenna a,*, Fabio Speranza b, Francesca D’Ajello Caracciolo a,Massimo Mattei a, Giacomo Oggiano c

aDipartimento di Scienze Geologiche, Universita di ‘‘Roma Tre,’’ Largo San Leonardo Murialdo 1, 00146 Rome, ItalybIstituto Nazionale di Geofisica e Vulcanologia, Rome, Italy

cIstituto di Scienze Geologico–Mineralogiche, Universita di Sassari, Sassari, Italy

Received 4 December 2001; accepted 17 May 2002

Abstract

Although the tectonic features and stress regime typical for accretionary complexes and back-arc domains have been widely

documented so far, few are known on the transitional zone separating these two systems. Here we report on structural analysis

and anisotropy of magnetic susceptibility (AMS) results from Eocene–Pliocene sediments exposed in western Sardinia. From

late Oligocene to middle Miocene, the studied area was located between the Alpine–Apennine wedge to the east, which was

undergoing shortening and accretion, and the Liguro–Provenc�al basin, undergoing extension and spreading. We find that, prior

to the formation of the Liguro–Provenc� al basin, the middle Eocene– lower Oligocene sediments cropping out at the

southwesternmost edge of Sardinia were subjected to NE–SW shortening (in present-day coordinates), in agreement with

recently reported geological information. Conversely, the upper Oligocene–Pliocene sedimentary sequences record a different

evolutionary stage of extensional processes. Upper Oligocene–middle–upper Burdigalian sediments clearly show a N–S-

oriented magnetic lineation that can be related to extensional direction along the prevalent E–W-oriented normal faults. On the

other hand, no magnetic lineation has been detected in upper Burdigalian–Serravallian sediments, which mark the end of the

first rifting process in Sardinia, which likely coincides with the rift-to-drift transition at the core of the Liguro–Provenc�al basin.Finally, a NE–SW extension is observed in two Tortonian–Pliocene sites at the northwestern margin of the NNW–SSE-

oriented Campidano graben. Our study confirms that AMS may represent a valuable strain-trajectory proxy and significantly

help to unravel the characters of temporally superimposed tectonic events.

D 2002 Elsevier Science B.V. All rights reserved.

Keywords: Back-arc basin; Magnetic anisotropy susceptibility (AMS); Sardinia; Mediterranean area

1. Introduction

The subduction process is associated with contrast-

ing styles of back-arc deformation that produces

mountain chains or extensional basins (Uyeda and

Kanamori, 1979; Jarrard, 1986). In the latter case, the

state of stress is expected to switch from compression

near the trench, where accretion of underthrusted

0040-1951/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved.

PII: S0040 -1951 (02 )00287 -1

* Corresponding author. Tel.: +39-654-888-029; fax: +39-654-

888-201.

E-mail addresses: [email protected] (C. Faccenna),

[email protected] (F. Speranza).

www.elsevier.com/locate/tecto

Tectonophysics 356 (2002) 213–232

sediments predominates, to extensional process near

the volcanic arc. In addition, extensional and com-

pressional directions in the different sectors of the

trench–arc system are expected to be subparallel and,

when subduction zones is not oblique, back-arc basins

usually extend perpendicularly to the direction of

trenches. The transition between those two domains

is poorly documented. Nakamura and Uyeda (1980)

first describe the presence of an ‘‘intermediate’’ strike-

slip regime in the area located between the trench and

the back-arc region. This is theoretically consistent

with a gradual change in the magnitude of the stress

tensor, but with one of the principal axes always

oriented parallel to the main direction of tectonic

motion.

In this paper, we will focus on a well-documented

example of a transitional regime, between compres-

sion at the trench and extension in the back-arc area.

Our analysis has been carried out in Sardinia. Sardinia

is located in the middle of the Mediterranean region

(Fig. 1) and has been extended and rifted apart from

the Iberian Peninsula during the opening of the

Liguro–Provenc�al basin, between 30 and 15 Ma

(Cherchi and Montadert, 1982). The southeastward

lateral drift and simultaneous counterclockwise rota-

tion of Sardinia is the consequence of the retreat of the

trench, presently active below Calabria (Malinverno

and Ryan, 1986), contemporaneously with accretion

and thrusting of the Apennine chain units (Patacca et

al., 1990).

We reconstruct the extensional direction during

the drifting and rotation of the Sardinia block

using the anisotropy of magnetic anisotropy sus-

ceptibility (AMS) and the analysis of fault popu-

lations, affecting Eocene–Pliocene sedimentary

deposits.

Fig. 1. Map of the central–western Mediterranean region showing volcanism and the Oligocene-to-present kinematics derived from the analysis

of deformation. Numbers describe the age of initiation and end of extension in the various basins. For a review of the data shown here, see

Jolivet and Faccenna (2000).

C. Faccenna et al. / Tectonophysics 356 (2002) 213–232214

Confirming previous reconstruction (Thomas and

Gennesseaux, 1986; Funedda et al., 2000), our results

show that western Sardinia was subjected to two main

extensional episodes. The first was between 25 and 18

Ma (late Oligocene–middle late Burdigalian) where

the island extended roughly NS (in present-day coor-

dinates), along an overall direction oriented parallel to

the trench and orthogonal to the back-arc extension in

the more internal Liguro–Provenc�al area. This epi-

sode was followed since 18 Ma (late Burdigalian–

Messinian) by another extensional episode different

from the previous not only in the direction (extension

EW and NS elongated basins) but also in that sub-

sidence is less intense. Afterwards, during the last 10

my, Sardinia underwent again a SW–NE extensional

episode, inducing the formation of the present-day

depression of the Campidano graben. These results

basically confirm that the Sardinia rifted area (the so-

called Sardinia trough) is the result of superimposed

extensional/transtensional episodes (Thomas and Gen-

nesseaux, 1986; Carmignani et al., 1995). However,

the direction of extension inferred here and the related

interpretation are in conflict with previous studies

(e.g., Cherchi and Montadert, 1982; Letouzey et al.,

1982), which propose that the first extensional (and

main) event was E–W directed.

2. Geological setting

Sardinia is a continental block surrounded by Neo-

gene ocean-floored basins: the Liguro–Provenc�albasin to the west and the Tyrrhenian Sea to the east

(Fig. 1). They opened in different times, first the

Liguro–Provenc�al (between 30 and 15 Ma) and then

the Tyrrhenian Sea (between 10–12 Ma and present).

The two basins share characters of back-arc basins

(Malinverno and Ryan, 1986), as attested by anom-

alous heat flow (Cataldi et al., 1995; Chamot-Rooke

et al., 1999), depth, volcanic suite (Beccaluva et al.,

1985, 1989), the presence of a Wadati–Benjoff zone,

presently active below Calabria (Selvaggi and Chiar-

abba, 1995), and by the fact that extensional process

occurred contemporaneously to wedge accretion in

the Apennine chain (Patacca et al., 1990). Geological

and paleomagnetic data indicate that Corsica–Sardi-

nia drifted apart from the Catalan–Provenc� al coastduring the opening of the Liguro–Provenc�al basin and

the retreat of the trench occurring between 21 and 15

Ma (Van der Voo, 1993; Vigliotti and Langenheim,

1995; Speranza, 1999; Deino et al., 2001). Over the

course of this rapid migration (up to 4–5 cm/year), the

Corsica–Sardinia block was left back in its present-

day position whereas the Calabrian block was carried

along with the retreating trench.

The presence of a continental block in the middle

of the Mediterranean offers an opportunity to inves-

tigate the way the extensional process related to back-

arc opening evolved with time during the episodic

rifting and drifting, and the way the deformation

evolved from the trench area towards the back-arc

region.

The Sardinia ‘‘trough’’ zone is a 55-km wide, 220-

km long roughly N–S elongated depression (Fig. 2),

filled up by more than 1000 m of clastic and carbonate

sediments, epiclastic, and volcanic rocks consisting of

andesites and dacitic–rhyolitic ignimbrites and tuffs

(Cherchi and Montadert, 1982; Assorgia et al., 1997).

Most of the pre-rift basement rocks are constituted of

Paleozoic metamorphic rocks deformed during the

Hercynian orogeny, upper Carboniferous–Permian

granitoids and Mesozoic platform carbonates deposits.

The trough itself results from by the interferences of

several, half-graben and strike-slip basins, mainly E–

W-oriented (Oggiano et al., 1995). Conversely, in the

eastern Sardinia, the pre-rift basement is cross-cut by

E–NE- and N–S-oriented faults with mainly strike-

slip and normal motion, respectively (Carmignani et

al., 1994).

The oldest marine sedimentary cycle, upper Pale-

ocene in age (Barca and Costamagna, 2000), uncon-

formably overlying the Mesozoic units, has been

drilled in the southwesternmost Sardinia (Sulcis). It

is followed by a slow regression and deposition of

lower–middle Eocene supratidal and paralic facies

limestones (Cherchi, 1983), affected by a system of

thrusts likely related to the Pyrenean orogeny (Barca

and Costamagna, 1997). These deposits are uncon-

formably covered by continental deposits of the

Cixerri Formation, formed by middle Eocene (Lute-

tian)– lower Oligocene conglomerates, sandstones,

and reddish silty sandstones sealing the main thrust

system (Barca and Costamagna, 1997), and covered

by volcanics dated between 28 and 30 Ma (Bellon et

al., 1977). The paleotectonic framework of the Cixerri

Formation is still debated, even if it is commonly

C. Faccenna et al. / Tectonophysics 356 (2002) 213–232 215

considered as a ‘‘molassic’’ deposits related to the

Pyrenean orogenic system (Cherchi, 1983; Barca and

Costamagna, 1997, 2000).

Four marine sedimentary cycles mark the onset of

the extensional process in Sardinia. All of them are

accompanied by volcanic activity.

Fig. 2. Geological map of Sardinia. The sites of structural and AMS analysis and the in situ magnetic lineation direction are also shown.


The first cycle started in the late Oligocene with

continental deposition followed by a local marine

ingression during the late Oligocene–early Aquita-

nian (Marmilla, Anglona, Funtanazza basins), with a

maximum deepening during the Aquitanian–Burdiga-

lian boundary. This sedimentary cycle lasted up to the

middle–upper Burdigalian and until lower Burdiga-

lian in the Anglona area (Francolini and Mazzei,

1991) where it is sealed by continental and pyroclastic

flow and lacustrine deposits (Assorgia et al., 1997,

and references therein). Most of the deposition of

these sediments occurred within E–W to E–NE-

trending basins, as Funtanazza in southwestern Sardi-

nia (site 03 in Fig. 2) or the Castelsardo basin in

northern Sardinia (site 30–35 in Fig. 2) (Francolini

and Mazzei, 1991; Oggiano et al., 1995; Cipollari and

Cosentino, 1997; Sowerbutts and Underhill, 1998). In

NE Sardinia, fine-grained lacustrine sediments with

marine intercalations and continental deposits of the

same age are deposited in the Chilivani–Berchidda

basin (site 36 in Fig. 2), which formed in correspond-

ence of a releasing bend along a major E–NE-trend-

ing strike-slip fault (Oggiano et al., 1995). Gravel and

boulder-sized continental conglomerates were depos-

ited in a similar strike-slip setting, at the border of

positive transpressive structure along the E–NE strik-

ing strike-slip faults of Mt. Albo (Carmignani et al.,

1994; Oggiano et al., 1995).

Upper Burdigalian–lower Serravallian sediments

forming the second marine cycle unconformably over-

lay the older sediments. The maximum deepening of

the sedimentary basin occurred during the early–

middle Langhian–early Serravallian, before a regres-

sive phase, causing the deposition of fluvio-marine

and infralittoral sediments (Martini et al., 1992). This

cycle corresponds to the ‘‘post-rift’’ succession of

Cherchi and Montadert (1982), although NNW–

SSW- and N–S-bearing normal faults control its

deposition within some relatively deep half-grabens.

Such grabens in northern Sardinia cross-cut the pre-

vious extensional/transtensional structures (Sower-

butts and Underhill, 1999; Funedda et al., 2000).

The third marine sedimentary cycle was deposited

during late Serravallian–early Messinian times in a

shelf environment, whereas the fourth and last short

cycle of marine sedimentation consists of by shelf-

environment Pliocene–Pleistocene marls and sandy

clays cropping out in few localities. The last sedi-

mentary cycle is related to the formation of the NNW

narrow and deep Campidano graben (Fig. 2), filled

by several kilometers of Pliocene–Pleistocene sedi-

ments.

In synthesis, the sedimentary cycles appear to be

related with various tectonic regimes, characterised

by different styles and orientation of the main

structures. The detailed reconstruction of these de-

formation episodes and their relationship with the

tectonic framework of the area is far from clear.

Some authors suggest that the first sedimentary cycle

was deposited in a strike-slip environment, related to

N–S compression (Carmignani et al., 1994), whereas

others (Cherchi and Montadert, 1982), relying on

microstructural analyses, proposed a sequence of

compressional and extensional events differently ori-

ented. The difficulty of unraveling the tectonic

evolution is due to the fact that the different de-

positional cycles and superimposed deformational

events obscure the structural architecture of the

basin.

In this framework, AMS results coupled with

microstructural analyses can provide key pieces of

evidence to reconstruct the structural history of this

area. The magnetic fabric has proven to be closely

related to the strain ellipsoid, both in compressional

and extensional regimes (e.g., Sagnotti and Speranza,

1993; Sagnotti et al., 1994, 1998; Scheepers and

Langereis, 1994; Mattei et al., 1997, 1999; Speranza

et al., 1999). Such analyses are of crucial importance

where the rocks are poorly deformed given the

absence or paucity of classical strain markers, and

they can be performed even in small outcrops (Lowrie

and Hirt, 1987). It has been shown that the magnetic

fabric is acquired a short time after the sediment

deposition, during the first tectonic events, and is

hardly modified by subsequent brittle deformational

events (Mattei et al., 1997). This AMS allows us to

separate tectonic phases, occurring in different times,

because it highlights each tectonic event synchronous

to (or shortly following) the deposition of a given

sedimentary unit. Conversely, such partition is often

difficult or impossible by solely using structural

analysis.

We sampled the Eocene–Oligocene Cixerri For-

mation and all the four sedimentary cycles in 36

different sites spread over Sardinia for AMS analyses

(Fig. 2). Seven sites have been drilled in the Cixerri


Formation, 16 in the first sedimentary cycle, 11 in the

second cycle, 1 in the third, and 1 in the fourth (Table

1). In each site (apart from site Sa02), we drilled 7 to

17 cores with an ASC-280E petrol-powered drill, and

oriented them in situ with a magnetic compass. In site

Sa02, 87 cores were sampled (Table 1).

3. Results

3.1. Anisotropy of magnetic susceptibility

The low-field magnetic susceptibility (k) of each

sample was measured with a KLY-2 bridge in the

Table 1

List of anisotropy factors computed at each site

Site Age N km L F PV

Sa01: I depositional cycle Lower Burdigalian 13 76.3 (33.3) 1.004 (0.002) 1.052 (0.022) 1.063 (0.026)


Sa03: I depositional cycle Aquitanian 17 4503.1 (3481.3) 1.004 (0.002) 1.052 (0.022) 1.063 (0.013)

Sa04: II depositional cycle Serravallian–Langhian 12 144.4 (3.5) 1.003 (0.002) 1.030 (0.004) 1.037 (0.005)

Sa05: II depositional cycle Upper Burdigalian 10 108.4 (11.1) 1.002 (0.001) 1.028 (0.004) 1.034 (0.005)

Sa06: II depositional cycle Serravallian 12 135.8 (7.7) 1.003 (0.001) 1.026 (0.005) 1.032 (0.006)

Sa07: Cixerri Formation Eocene–Oligocene 10 201.8 (14.1) 1.008 (0.002) 1.008 (0.002) 1.016 (0.003)



Sa10 Eocene 10 114.2 (10.6) 1.023 (0.003) 1.003 (0.001) 1.029 (0.004)




Sa14: III depositional cycle Tortonian 12 108.5 (3.3) 1.003 (0.002) 1.023 (0.002) 1.029 (0.003)

Sa15: IV depositional cycle Pliocene 8 88.7 (3.3) 1.002 (0.001) 1.024 (0.002) 1.029 (0.003)

Sa16: II depositional cycle Langhian 12 123.4 (8.6) 1.065 (0.007) 1.004 (0.002) 1.078 (0.008)




Sa20: II depositional cycle Upper Burdigalian 9 121.7 (9.7) 1.003 (0.002) 1.019 (0.002) 1.024 (0.002)

Sa21: I depositional cycle Oligocene–Aquitanian 10 201.5 (17.1) 1.003 (0.001) 1.042 (0.014) 1.050 (0.016)




Sa25: I depositional cycle Upper Burdigalian–Langhian 10 81.3 (7.3) 1.003 (0.001) 1.037 (0.003) 1.044 (0.004)







Sa32: I depositional cycle Oligocene 10 50.1 (12.7) 1.006 (0.005) 1.008 (0.004) 1.014 (0.007)

Sa33: I depositional cycle Aquitanian 9 3137 (436) 1.005 (0.002) 1.033 (0.011) 1.042 (0.013)




N= number of specimens; km=(kmax + kint + kmin)/3 (mean susceptibility, in 10� 6 SI units); L= kmax/kint; F = kint/kmin; PJ = exp{2[(g1� g)2+(g2�g)2+(g3� g)2]}1/2 (corrected anisotropy degree; Jelinek, 1981); T= 2(g2� g3)/(g1� g3)� 1 (shape factor; Jelinek, 1981); S0 = bedding

attitude (azimuth of the dip and dip values); g1 = ln kmax; g2 = ln kint; g3 = ln kmin; g=(g1 + g2 + g3)/3, E1 – 3, E2 – 3, E1 – 2 = semiangles of the 95%

confidence ellipses around the principal susceptibility axes. For each locality, the arithmetic means of the individual site mean values are

shown (standard deviation in parentheses).


paleomagnetic laboratory of the Istituto Nazionale di

Geofisica e Vulcanologia. The AMS at both the speci-

men and the site level was evaluated using Jelinek

(1978) statistics. In each site, the anisotropy degree and

the shape of the susceptibility ellipsoids were evaluated

by means of the PV and T parameters (Jelinek, 1981),

respectively. The k values are always low ( < 250�10� 6 SI, Fig. 3a and Table 1), except in sites Sa03 and

Sa33 (both Aquitanian in age), where they are as high

as 4503� 10� 6 and 3137� 10� 6 SI, respectively.

As for previous studies performed in clayey–marly

sediments in the Italian peninsula and Sicily (e.g.,

T S0 D, I (kmin) D, I (kmax) E1 – 3 E2 – 3 E1 – 2 Structural analysis

and notes

0.821 (0.141) 310, 15 246, 83 358, 3 3.7 3.1 17.3 no

0.642 (0.214) 64, 21 318, 76 165, 13 5.4 5.3 11.7 yes

0.751 (0.086) 269, 33 97, 59 294, 30 1.6 2.1 11.6 no

0.792 (0.082) not visible 293, 78 146, 10 2.1 2.3 17.4 no

0.885 (0.080) 88, 10 7, 78 277, 0 7.4 2.8 36.4 no

0.815 (0.073) 190, 25 213, 82 111, 2 9.2 4.2 23.0 yes

0.039 (0.244) not visible 22, 82 132, 3 9.0 3.7 26.0 yes

0.342 (0.362) subhorizontal 213, 7 304, 8 6.1 28.0 22.0 yes

0.273 (0.436) not visible 79, 1 348, 40 8.4 19.7 34.0 no

0.757 (0.090) 240, 9 63, 0 154, 77 3.7 19.1 11.3 no– inverse fabric


0.839 (0.099) subhorizontal 162, 88 350, 2 2.3 3.9 15.6 no


0.756 (0.095) not visible 106, 82 222, 4 2.4 3.3 10.2 yes

0.828 (0.048) 57, 32 313, 59 215, 5 8.9 13.6 26.2 yes

0.886 (0.051) subhorizontal 264, 1 6, 84 2.8 13.5 5.6 no– inverse fabric

0.117 (0.354) not visible 352, 77 102, 5 18.6 26.6 21.8 no



0.751 (0.141) not visible 278, 29 125, 10 3.6 6.5 53.9 no

0.846 (0.092) 330, 15 231, 73 27, 16 3.4 8.5 25.1 yes

0.118 (0.366) 4, 15 144, 61 31, 12 21.0 45.2 31.0 no

0.819 (0.106) subhorizontal 314, 8 161, 5 2.7 4.7 43.1 no

0.635 (0.12) 2, 24 216, 62 346, 19 2.1 4.2 12.8 no

0.871 (0.064) 76, 8 280, 87 64, 3 2.5 9.6 38.4 no

0.485 (0.123) subhorizontal 299, 68 185, 9 4 12 18 no




0.863 (0.054) subhorizontal 61, 88 186, 1 6 3 21 yes


0.118 (0.355) 221, 12 156, 84 269, 2 10 16 21 no

0.699 (0.123) 321, 15 278, 69 62, 17 7 5 49 yes

0.171 (0.427) 332, 15 130, 74 249, 8 15 22 37 no

0.656 (0.249) 326, 18 33, 84 182, 5 9 8 42 yes



Scheepers and Langereis, 1994; Sagnotti et al., 1998;

Speranza et al., 1999), the question arises as to

whether the measured fabric reflects the anisotropy

of the clay matrix minerals, the ferrimagnetic miner-

als, or both. Sagnotti et al. (1998) and Speranza et al.

(1999) observed that the low-field susceptibility (and

AMS) is likely to be significantly influenced by the

ferrimagnetic susceptibility only when the k values are

higher than 200� 10 � 6 to 300� 10 � 6 SI. The

ferrimagnetic mineral susceptibility adds to the sus-

ceptibility ‘‘base level’’ due to the paramagnetic clays,

which seems to be dominant in the samples having

k < 200� 10� 6 to 300� 10� 6 SI.

The dominant role of the paramagnetic minerals as

carriers of the susceptibility and AMS is confirmed by

the hysteresis properties measured using a Molspin

VSM in three samples from three different sites (Fig.

4). One of these sites (Sa09) shows the highest PVvalue (1.109, Table 1), and another one (Sa16) shows

an inverse fabric (see below). Both the high aniso-

tropy and the inverse fabric might, in principle,

suggest a significant ferromagnetic contribution to

the low-field susceptibility (single-domain magnetite

commonly carries the inverse fabric). All the three

samples show no hysteresis (i.e., a line passing

through the origin, Fig. 4), showing a typical para-

magnetic behaviour. Given the sole paramagnetic

contribution, the inverse fabric shown at two sites

(see below) is likely due to Fe-bearing carbonates, as

also documented elsewhere in Italy (e.g., Winkler et

al., 1996), and not to single-domain magnetite.

The ferrimagnetic contribution is likely significant

only in the sites Sa03 and Sa33, showing k values

much higher (of about one order of magnitude) than

the other sites (Table 1). Site Sa03 was sampled in

porous calcarenite beds cut by calc–alkaline dykes.

Therefore, we infer that in such site hot fluids from the

dykes saturated the adjacent porous sediments and

Fig. 3. (a) Frequency distribution of the mean susceptibility (km) in the sediments investigated in this study; (b) L/F plot for all the studied

samples; (c) lower hemisphere, equal area plots for an example of a site showing a subvertical lineation orthogonal to bedding (inverse magnetic

fabric, e.g., Rochette et al., 1992); (d) example of a site showing a well-defined magnetic foliation parallel to bedding and a well-defined

tectonic-related magnetic lineation.


filled with material that includes ferrimagnetic miner-

als. Conversely, site Sa33 was sampled in a sedimen-

tary–volcanoclastic succession containing several ash

layers. Here the high k value likely arises from the

volcanic fraction, rich in ferrimagnetic minerals.

The anisotropy degree PVis always low (Table 1),

with values typical of weakly deformed sediments

(PVV 1.109). The shape of the AMS ellipsoids is

predominantly in the oblate field (T>0 or F>L, Fig.

3b) except at sites Sa10 and Sa16, where it is almost

purely prolate (T=� 0.757 and � 0.886, respectively,

Fig. 3b and Table 1). In these two sites, the magnetic

lineation is vertical (Fig. 3c) and orthogonal to bed-

ding (and the sediments are almost undeformed),

implying that here the magnetic fabric is inverse,

and no simple correlation between the magnetic fabric

and the rock fabric exists (e.g., Rochette et al., 1992).

In almost all sites (except Sa08, Sa09, Sa10, and

Sa16), despite the low magnetic anisotropy, the mag-

netic foliation plane is generally well defined and

parallel to the bedding plane (Fig. 3d), as it is

commonly observed in weakly deformed sediments.

The magnetic foliation is perpendicular to the bedding

plane only in the sites Sa08 and Sa09 (Fig. 2),

sampled in the Cixerri Formation. These are the oldest

sediments studied by us and underwent a more com-

plex tectonic history than the other formations (see

Discussion).

The magnetic lineation is well defined in 21 sites

(Figs. 2 and 3 and Table 1), where the e12 confidence

angle of the kmax in the kmax–kint plane is < 30j. Theremaining 13 sites have a purely oblate fabric with

virtually no lineation (e12>30j).The tectonic implications for the presence and

direction of the magnetic lineation in the different sites

will be fully discussed in Sections 4 and 5. We will

present in detail the magnetic fabric characters shared

by the sites from each sedimentary cycle, below,

together with the results of the fault population anal-

ysis carried out on the same sites sampled for AMS.

3.2. AMS and structural analysis of the Cixerri

Formation

The Cixerri Formation crops out in the Iglesiente

and Sulcis areas, in southwestern Sardinia (Figs. 2 and

5A). Two sites, Sa08 and Sa09, close to the south-

western coast, show magnetic foliation subvertical

and perpendicular to the bedding plane (Fig. 6). The

magnetic foliation perpendicular to the bedding planes

has been generally related to the passive displacement

and rotation of hematite and clay minerals within

cleavage planes (Graham, 1966; Kligfield et al.,

1981; Pares et al., 1999). In these cases, it was

demonstrated that magnetic foliation is perpendicular

to the maximum shortening direction (r1). We found

Fig. 4. Hysteresis loops measured using a Molspin VSM for three

samples coming from three different sites. All the three plots show

no hysteresis and a typical paramagnetic behaviour.


Fig. 5. Detailed geological map and in situ magnetic lineation from the Marmilla–Campidano (A) and Anglona–Logudoro (B) areas.

C.Faccen

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al./Tecto

nophysics

356(2002)213–232

222

microstructural evidence of low angle reverse faults

(striae azimuth oriented N40–50j, Fig. 6b) cross-cutby subsequent extensional faults at site Sa08 (Fig. 6c).

Barca and Costamagna (1997, 2000) describe Eocene

thrusting spread over the area. In compressional set-

ting, the magnetic lineation forms parallel to fold

axes, and thrust sheet, that is almost perpendicular

to the maximum horizontal shortening. The two sites

show a lineation ranging between N–S and NW–SE,

even if Sa09 lineation is not well defined (e12 = 34j,Table 1). Four other sites (Sa07, Sa17, Sa18, and

Sa19) of the Cixerri Formation have a foliation

parallel to bedding and magnetic lineation ranging

from N to NW (Figs. 2 and 5a). Site Sa18 is also

affected by a set of E–Wextensional joints orthogonal

to the kmax axis. As a whole, the Cixerri Formation

sites in the Iglesiente–Sulcis area define an average

N146j magnetic lineation suggesting a NE compres-

sion, as also confirmed by structural data (Barca and

Costamagna, 1997, 2000).

3.3. AMS and structural analysis of the first

sedimentary cycle

The units belonging to the first cycle crop out

along the Sardinian trough (Fig. 1) in the Marmilla

(Fig. 5A) and Anglona areas (Fig. 5B), and tradition-

ally have been considered as a marker for the onset of

the ‘‘rifting’’ episode. Nine sites have been sampled in

the Marmilla area (Fig. 5A) in both continental upper

Oligocene–Aquitanian basal units (Sa21 and Sa24)

and in the marine lower–middle Burdigalian marls.

Five sites yield a well-defined N–S lineation, in

agreement with structural analysis results from some

sites (for example, site Sa02 or Sa11; Fig. 7a,b),

showing that syn-sedimentary faults and extensional

joints are E–W to E–NE striking. The computed

extensional direction, between NS and N10jW, is in

good agreement with the orientation of the kmax axis.

Six sites have been drilled in the Anglona area

(Fig. 5B) and in the Chilivani basin (Fig. 2) in both

continental upper Oligocene–Aquitanian sediments

(Sa32 and Sa36) and in marine Aquitanian–Burdiga-

lian marls interbedded with volcanoclastic debris. In

the continental sediments, the magnetic lineation is

EW in site Sa32 and NE in site Sa36. The latter site

has been drilled in a releasing bend along a major NE

strike-slip fault (Oggiano et al., 1995). One site has

been drilled in the EW striking half-graben Funta-

nazza basin (Sa03; Fig. 2).

Two out of the five sites drilled in the marine units

show a well-defined magnetic lineation, N–S striking

(Figs. 2 and 5b). Microstructural analysis in those

sites systematically showed EW striking syn-sedimen-

Fig. 6. Magnetic fabric (a) and structural analysis (b,c) from site Sa08 (Cixerri Formation, middle Eocene– lower Oligocene). Normal faults

shown in the diagram (c) cross-cut the reverse faults shown in diagram (b). AMS and structural data are reported on equal-area, lower

hemisphere net.


tary normal faults and a N–S extensional direction. In

many of the sampled sites, this first deformational

episode is followed by system of NNW–SSE-oriented

normal faults and joints (see, for example, site Sa30,

Fig. 7c).

3.4. AMS and structural analysis of the second

sedimentary cycle

Four sites (Sa04, Sa05, Sa06, and Sa20) were

sampled in Langhian–Serravallian marine marls from

southern Marmilla region (Figs. 2 and 5a). Only site

Sa06 showed a WNW–ESE lineation, whereas the

remaining three showed a purely oblate fabric. In the

Anglona area and east of Monte Ferru, six sites were

sampled in clayey–marly beds interbedded with a

monotonous and thick sequence of coastal sandstones,

Langhian in age (Figs. 2 and 5b). One site (Sa16)

shows an inverse fabric (Fig. 3c), with the magnetic

lineation subvertical and perpendicular to bedding.

Out of the remaining six sites, two (Sa26 and Sa28)

show a N–S magnetic lineation, while the other four

(Sa25, Sa27, Sa29, Sa34) have a purely oblate fabric.

3.5. AMS and structural analysis of the third and

fourth sedimentary cycles

Two sites (Sa14 and Sa15) were sampled in Torto-

nian and lower Pliocene marine clays, respectively, in

the northwestern margin of the Campidano graben

(Fig. 2). These two sites show a well-defined NE–SE

magnetic lineation, in agreement with structural anal-

ysis data documenting NW–SE-oriented joints (Fig.

7).

4. Interpretation of the magnetic lineation

directions and structural data

The magnetic lineation direction has been widely

used in many Miocene to Pleistocene clay deposits

from the external Apennines (Sagnotti and Speranza,

1993; Sagnotti et al., 1998; Scheepers and Langereis,

1994; Mattei et al., 1997) and the extensional margin

of the central Apennines (Sagnotti et al., 1994) and

Calabria (Scheepers and Langereis, 1994; Mattei et al.,

1999) to understand the tectonic history. Here the

magnetic lineation has proven to be a faithful strain-

trajectory proxy and to represent a fundamental struc-

tural tool to unravel the strain history in sediments

lacking other visible structural elements (e.g., faults,

cleavage, fractures). It has been shown that in foredeep

clays interbedded in turbidite sequences and in thrust-

top deposits, the magnetic lineation forms shortly after

compression and faithfully represents the local fold

axis direction (e.g., Mattei et al., 1997, with referen-

ces). Conversely, in extensional syn-rift deposits, the

magnetic lineation is orthogonal to the extensional

faults and parallel to the stretching direction.

On the base of our AMS and structural data set, we

are able to characterise the tectonic regime that

accompanied the deposition of the different sedimen-

tary cycles. Our data show that:

(a) The Eocene–Oligocene Cixerri Formation was

deposited during the final stages of a compressional

episode, which is in agreement with the hypothesis of

Barca and Costamagna (2000). A mean magnetic

lineation, oriented on average NW–SE (Figs. 2, 5a,

and 9a), should reflect the maximum compression,

oriented NE–SW. To imagine its original orientation

Sardinia has to be clockwise rotated back clockwise

by about 30j restoring the island to its previous pre-

drifting position (e.g., Van der Voo, 1993; Speranza,

1999). Our data set can be interpreted in the light of

two different models proposed for the area. In the first

model, the Cixerri Formation was deposited in the

distal part of a continental foredeep basin, tentatively

correlated with the southernmost continuation of the

Pyrenean foredeep basin (Barca and Costamagna,

2000). Alternative model is that the Cixerri Formation

was deposited in transpressional basin, related to

large-scale strike-slip faults (Carmignani et al., 1999).

(b) The first upper Oligocene– lower Miocene

marine transgression in Sardinia marked the onset of

extensional process (Assorgia et al., 1997). The direc-

tion of magnetic lineation, from several sites scattered

Fig. 7. AMS and structural analysis results from (a) site Sa02 (lower Burdigalian), from (b) site Sa30 (Aquitanian) and (c) site Sa30 (upper

Oligocene–Aquitanian). In the latter site, we also show the structural analysis of two different deformative episodes, characterized by syn-

sedimentary normal fault (middle) and, successively, by N20jW striking normal faults and joints (right). AMS and structural data are reported

on equal-area, lower hemisphere net.


over the entire island, is well clustered around N10–

20jW (Fig. 9b). In addition, fault population analysis

and the presence of E–W-oriented extensional sedi-

mentary basins, suggest that the deposition of the

upper Oligocene–lower Miocene sedimentary succes-

sions occurred under a roughly N–S extensional

regime. In agreement with Carmignani et al. (1995),

we then confirm that the present-day N–S orientation

of the ‘‘Sardinian trough’’ axis does not reflect the

trend of the main upper Oligocene to middle–late

Burdigalian sedimentary basins.

Oggiano et al. (1995), by studying one of the

extensional basins (Chilivani–Berchidda, site 36 of

Fig. 2), suggested that the E–W normal fault are

related to a releasing bend along a E–NE-trending

strike-slip fault (Fig. 1). These faults cross-cut all the

eastern side of the island and are marked by both

releasing and restraining bends (Carmignani et al.,

1994, 1995; Oggiano et al., 1995). Some of them

show a main sinistral sense of motion (as the one

bordering Mt. Albo, Carmignani et al., 1994, 1995),

though careful analysis of kinematics indicators along

the major fault planes (e.g., Mt. Albo) indicates that

dextral motion is locally superimposed on the sinistral

one. Syn-tectonic continental deposits, in addition,

indicate that the activity of these major strike-slip

faults occurred during the sedimentation of the first

marine cycle and are possibly reactivated as transfer

faults connecting different NNW-trending upper Bur-

digalian basins (Funedda et al., 2000).

Our data set indicates that the first upper Oligo-

cene–lower Miocene marine cycle filled E–W striking

Fig. 8. AMS and structural analysis of sites Sa14 (Tortonian) and Sa15 (Pliocene). AMS and structural data are reported on equal-area, lower

hemisphere net.


(N–S extensional direction in present-day orientation)

transtensional basin is mainly located along the west-

ern side of the island. Conversely, a strike-slip regime

was predominant at the same time over the eastern side

of the island. We then confirm previous suggestion

(Carmignani et al., 1995) that an overall late Oligo-

cene–early Miocene N–S extensional episode evolved

from transtension in western Sardinia to strike-slip

deformational style moving towards the east.

Different models can be proposed in order to

explain the apparent contradiction between the exten-

sional direction, as estimated in the western side of

island inside the E–W extensional basin and the one

estimated along the major strike-slip fault zones

present in the eastern side of the island. The first

model interpreted the origin of the E–W extensional

basin as kinematically related to releasing bend along

NE-bearing sinistral strike-slip faults (Carmignani et

al., 1995; Oggiano et al., 1995). An alternative

hypothesis proposed here suggests that the whole

region is subjected to a N–S extensional episode

parallel to the strike of the island and that complex

interplay between the strike-slip fault system locally

generates the sinistral sense of motion along the E–

NE-bearing faults, as observed along the Mt. Albo

area (Pasci, 1997). The overall trend of the fault

zone, showing a sinistral ovestepping restraining

bend, and the presence of superimposed dextral kine-

matic indicator could suggest a more complex kine-

matic history of the Mt. Albo fault zone than pre-

viously supposed.

The data set collected here cannot discern between

the two models and further investigations are needed.

For example, it would be interesting to integrate our

data set with other sites located far away from the

main shear zones and in Corsica. More detail of the

kinematic analysis along the eastern Sardinia strike-

slip structures would also be useful.

(c) The second upper Burdigalian–lower Serraval-

lian depositional cycle occurred in less subsiding

basins, i.e., during Sardinian drift and oceanic spread-

ing in the Liguro–Provenc�al basin. The direction of

the magnetic lineation is dispersed, implying lack of a

well-defined stretching regime during the sediment

deposition (Fig. 9c). Microstructural and geological

data show, especially in the northern region, that N–S

high-angle normal faults and joints characterised the

second deformational episode in that area (Funedda et

Fig. 9. Frequency histograms of the magnetic lineation direction for all the studied samples.


al., 2000). It is then possible that the present-day N–S

striking orientation of the ‘‘Sardinian trough’’ formed

during the deposition of this second sedimentary

cycle. It is worth noting, however, that the lack of

well-defined magnetic lineations indicates that this

stretching episode has minor relevance over the

island.

(d) The Tortonian (site Sa14) and Pliocene (site

Sa15) sites sampled at the northwestern margin of the

Campidano graben (Fig. 2) show both a well-defined

magnetic lineation clustered around the direction

N40jE (Figs. 8 and 9d). This direction is parallel to

the pole to extensional joints observed in both sites

(Fig. 8) and almost orthogonal to the orientation of the

Campidano graben. These data show that the Campi-

dano graben formed in a pure NE–SW extensional

regime. Moreover, the Tortonian age of site Sa14 may

suggest that extension in the Campidano graben

begun already during Tortonian, i.e., significantly

earlier than the Pliocene age considered so far.

5. Insight into tectonic evolution of the

Mediterranean trench–arc–back-arc system

The microstructural analysis and the study of the

magnetic fabric of the Eocene–Pliocene sedimentary

sequences from Sardinia have tectonic implications in

the framework of central Mediterranean evolution.

The Tertiary evolution of the area started in the late

Paleogene with the deposition of thick sequences of

continental deposits. Our analysis confirm the pre-

vious interpretation that related these deposits to a

compressional setting in the foreland of the Pyrenean

belt or further east, in strike-slip transpressional basins

(Fig. 10, stage a). Our data confirm that Sardinia was

subjected to rifting from Oligocene to middle–late

Burdigalian times during the deposition of the first

sedimentary cycle. The systematic pattern of magnetic

lineation oriented between N–S and N20jWobserved

over the entire western side of the Island, coupled

with systematic microstructural observation and large-

scale basin geometry reconstruction (Oggiano et al.,

1995), indicate that transtensional tectonics affected

western Sardinia, with a maximum extension axis

oriented N–S (in present-day coordinates). The exten-

sional stretching axis, prior to the Sardinia counter-

clockwise rotation, was therefore oriented NE–SW.

This pattern of deformation is in contrast to what

observed along the western shoulder of the basin, that

is the Catalonia–Provenc�al area, i.e., along the west-

ern shoulder of the Liguro–Provenc�al basin. Here,

microstructural observation and large-scale basin

architecture (Seranne, 1999) indicate that a main

NW–SE extensional direction controlled the deposi-

tion of the first sedimentary cycle. This deformational

pattern is also in contrast with that observed in the

fragmented Alpine chain from Corsica to Calabria,

where interval accretion and high-pressure metamor-

phic units were forming at the same time (Carmignani

and Kligfield, 1990; Jolivet et al., 1998; Rossetti et al.,

2001). The depicted scenario thus shows a progressive

change in the deformational regime from compression

in the accreting wedge of Calabria, to strike-slip and

transtension in moving from eastern to western Sardi-

nia, to pure extension in the back-arc area (Fig. 10,

stage b). Carmignani et al. (1995) interpret this change

of the style of deformation as due to lateral escape

processes related to a collisional event. Here we

proposed an alternative interpretation related to the

change in the deformational regime as due to a

permutation of the stress axis. The minimum compres-

sional axis, vertical in the accretionary prism, be-

comes horizontal in the back-arc area where it

strikes perpendicularly to the trench. The Sardinia

region is located between these two well-defined

deformational regimes and is dominated by an inter-

mediate state of deformation and of stress character-

ised by a strike-slip to transtensional regime with a

minimum compressional axis oriented parallel to the

trench. This transitional regime can be compared to

the one describe for the Japan area by Nakamura and

Uyeda (1980) where a progressive transition from

accretion in the trench area to back-arc extension

was documented. Our data also indicate that the

present-day major geomorphic features of Sardinia

have been acquired only during the last extensional

episodes. They occurred during and after the drifting

of the Island, with a passive subsidence and formation

of the main N–S-oriented depression that controlled

the deposition of the second sedimentary cycle (Fig.

10, stage c). The last tectonic episode, probably

started during the late Miocene, caused the formation

of the Campidano basin filled up by the third and

fourth sedimentary cycles. The origin of this deep

half-graben structure is poorly understood as it cannot


Fig. 10. Schematic block-diagrams showing the inferred tectonic scenario of the arc–back-arc system in the central–western Mediterranean at

three stages, from 35 to 15 Ma.


be directly related to the dynamic of the subduction

system.

6. Conclusions

We have shown that AMS, coupled with classical

structural analysis, represents a powerful tool to

define the characters of tectonic episodes affecting

in subsequent times a given region. The magnetic

fabric is sensitive to the strain trajectories produced

by a regime acting during or shortly after the sedi-

ment deposition. Therefore, use of AMS data is

advisable when structural analysis alone is unable to

unravel features of temporally superimposed tectonic

events.

Our structural/AMS data set demonstrates that

the arc–back-arc transition in western Sardinia was

accompanied by orogen-parallel extension. This tec-

tonic regime involved both NE–SW strike-slip faults

close to the Alpine–Apennine accretionary wedge

and N–S extension (both in present-day coordinates)

in the western part of the island, close to the

contemporaneously rifting Liguro–Provenc�al basin.

Therefore, we document here that the accretionary

wedge, the arc domain, and the back-arc basin were

characterised by a progressive shift from orogen-

normal shortening, orogen-parallel extension, and

orogen-normal extension, respectively. We also show

that in western Sardinia a N–S elongated volcanic

arc did not form along an E–W extending basin, the

so-called Sardinia trough, but was spatially super-

imposed over several coalescing N–S extending

grabens of Aquitanian–lower Burdigalian age. The

pre-upper Burdigalian sediments are unconformably

covered by virtually underformed middle–upper

Miocene successions, lacking any visible and mag-

netically retrievable deformation. We interpret this

late Burdigalian tectonic regime change as the inland

reflection of the rift-to-drift transition in the Liguro–

Provenc�al basin.

Acknowledgements

We thank R. Funiciello, for having encouraged this

work, and M. Musacchio, for help in the field. Fault

population analysis has been performed using the

Daisy programme, kindly provided by F. Salvini.

Thanks also to A. Winkler for performing the

hysteresis loops. The paper benefited from careful

reviews by A.M. Hirt and L. Carmignani.

References

Assorgia, A., Barca, S., Spano, C., 1997. A synthesis on the Cen-

ozoic stratigraphic, tectonic and volcanic evolution in Sardinia

(Italy). Boll. Soc. Geol. Ital. 116, 407–420.

Barca, S., Costamagna, L.G., 1997. Compressive ‘‘Alpine’’ tecton-

ics in western Sardinia: geodynamic consequences. C.R. Acad.

Sci., Paris 325, 791–797.

Barca, S., Costamagna, L.G., 2000. Il Bacino paleogenico del Sul-

cis– Iglesiente (Sardegna SW): nuovi dati stratigrafico–struttur-

ali per un modello geodinamico nell’ambito dell’orogenesi

pirenaica. Boll. Soc. Geol. Ital. 119, 497–515.

Beccaluva, L., Civetta, L., Maciotta, G., Ricci, C.A., 1985. Geo-

chronology in Sardinia: results and problems. Rend. Soc. Ital.

Mineral. Petrol. 40, 57–72.

Beccaluva, L., Brotzu, P., Macciotta, G., Morbidelli, L., Serri, G.,

Traversa, G., 1989. Cainozoic tectono-magmatic evolution and

inferred mantle sources in the Sardo-Tyrrhenian area. In: Bor-

iani, A., Bonafede, M., Piccardo, G.B., Vai, G.B. (Eds.), The

Lithosphere in Italy. Advances in Science Research. Accademia

Nazionale dei Lincei, Rome, pp. 229–248.

Bellon, H., Coulon, C., Edel, J.B., 1977. Le deplacement de la

Sardaigne. Synthese des donnees geochronologiques, magma-

tiques, et paleomagnetiques. Bull. Soc. Geol. Fr. 19, 825–831.

Carmignani, L., Kligfield, R., 1990. Crustal extension in the North-

ern Apennines: the transition from compression to extension in

the Alpi Apuane core complex. Tectonics 9, 1275–1303.

Carmignani, L., Barca, S., Disperati, L., Fantozzi, P., Funedda, A.,

Oggiano, G., Pasci, S., 1994. Tertiary compression and exten-

sion in the Sardinian basement. Boll. Geofis. Teor. Appl. 36,

141–144.

Carmignani, L., Decandia, F.A., Disperati, L., Fantozzi, P., Lazzar-

otto, A., Liotta, D., Oggiano, G., 1995. Relationships between

the tertiary structural evolution of the Sardinia –Corsica –

Provenc�al domain and the northern Apennines. Terra Nova 7,

128–137.

Carmignani, L., Funedda, A., Oggiano, G., Padsci, S., 1999. Una

nuova interpretazione strutturale dei bacini terziari del Cixerri e

di Narcao (Sardegna Occidentale). Abstract meeting GeoItalia,

2jForum FIST, vol. 1, pp. 415–417.

Cataldi, R., Mongelli, F., Squarci, P., Taffi, L., Zito, G., Calore, C.,

1995. Geothermal ranking of Italian territory. Geothermics 24

(1), 115–129.

Chamot-Rooke, N., Gaulier, J.-M., Jestin, F., 1999. Constraints on

Moho depth and crustal thickness in the Liguro–Provenc�albasin from a 3D gravity inversion: geodynamic implications.

In: Durand, B., Jolivet, L., Horvath, F., Seranne, M. (Eds.),

The Mediterranean Basins: Tertiary Extension Within the Al-

pine Orogen. Geol. Soc. London, Spec. Publ., vol. 156, pp.

37–61.


Cherchi, A., 1983. Presenza di Ilerdiano a Alveolinidae e Orbitoli-

nidae nel bacino paleogenico del Sulcis (Sardegna SW). Boll.

Soc. Sarda Sci. Nat. 22, 107–119.

Cherchi, A., Montadert, L., 1982. Oligo-Miocene rift of Sardinia

and the early history of the western Mediterranean basin. Nature

298, 736–739.

Cipollari, P., Cosentino, D., 1997. Caratteristiche stratigrafiche della

Formazione della Marmilla (Miocene inferiore) nell’area di Col-

linas-Villanova Forru (Sardegna centro-meridionale). Abstract

meeting ‘‘La Fossa Sarda’’ nell’ambito dell’evoluzione geodina-

mica cenozoica del Mediterraneo Occidentale, Villanovaforru,

1997, pp. 78–79.

Deino, A., Gattacceca, J., Rizzo, R., Montanari, A., 2001. 40Ar/39Ar

dating and paleomagnetism of the Miocene volcanic succession

of Monte Furru (western Sardinia): implications for the rotation

history of the Corsica–Sardinia microplate. Geophys. Res. Lett.

28 (17), 3373–3376.

Francolini, L., Mazzei, R., 1991. Inquadramento bio-crono-strati-

grafico delle tufiti marine del Miocene inferiore affioranti

nell’area di Castelsardo (Sardegna occidentale). Atti Soc. Tosca-

na Sci. Nat. Resid. Pisa, Mem., Serie A 98, 327–338.

Funedda, A., Oggiano, G., Pasci, S., 2000. The Logudoro basin: a

key area for the tertiary tectono-sedimentary evolution of North

Sardinia. Boll. Soc. Geol. Ital. 119, 31–38.

Graham, J.W., 1966. Significance of magnetic anisotropy in Appa-

lachian sedimentary rocks. Am. Geophys. Union Monogr. 10,

627–648.

Jarrard, R.D., 1986. Relations among subduction parameters. Rev.

Geophys. 24, 217–284.

Jelinek, V., 1978. Statistical processing of anisotropy of magnetic

susceptibility measured on a group of specimens and its appli-

cations. Stud. Geophys. Geod. 22, 50–62.

Jelinek, V., 1981. Characterization of the magnetic fabrics of rocks.

Tectonophysics 79, 63–67.

Jolivet, L., Faccenna, C., 2000. Mediterranean extension and the

Africa–Eurasia collision. Tectonics 19 (6), 1095–1106.

Jolivet, L., Faccenna, C., Goffe, B., et al., 1998. Midcrustal shear

zones in postorogenic extension: example from the northern

Tyrrhenian Sea. J. Geophys. Res. 103 (B6), 12123–12161.

Kligfield, R., Owens, W.H., Lowrie, W., 1981. Magnetic suscepti-

bility anisotropy, strain, and progressive deformation in Permian

sediments from the Maritime Alps (France). Earth Planet. Sci.

Lett. 55, 181–189.

Letouzey, J., Wanenesson, J., Cherchi, A., 1982. Apport de la mi-

crotectonique au problem de la rotation du bloc corso–sarde.

C.R. Acad. Sci., Paris 294, 595–602.

Lowrie, W., Hirt, A.M., 1987. Anisotropy of magnetic susceptibility

in the Scaglia Rossa pelagic limestone. Earth Planet. Sci. Lett.

82, 349–356.

Malinverno, A., Ryan, W.B.F., 1986. Extension in the Tyrrhenian

Sea and shortening in the Apennines as result of arc migration

driven by sinking of the lithosphere. Tectonics 5, 227–245.

Martini, P., Oggiano, G., Mazzi, R., 1992. Siliciclastic–carbonate

sequences of Miocene grabens in northern Sardinia, Western

Mediterranean Sea. Sedim. Geol. 76, 63–78.

Mattei, M., Sagnotti, L., Faccenna, C., Funiciello, R., 1997. Mag-

netic fabric of weakly deformed clayey sediments in the Italian

peninsula: relationships with compressional and extensional tec-

tonics. Tectonophysics 271, 107–122.

Mattei, M., Speranza, F., Argentieri, A., Rossetti, F., Sagnotti, L.,

Funiciello, R., 1999. Extensional tectonics in the Amantea basin

(Calabria, Italy): a comparison between structural and magnetic

anisotropy data. Tectonophysics 307, 33–49.

Nakamura, K., Uyeda, S., 1980. Stress gradient in back arc regions

and plate subduction. J. Geophys. Res. 85, 6419–6428.

Oggiano, G., Pasci, S., Funedda, A., 1995. Il Bacino di Chilivani-

Berchidda: un esempio di struttura transtensiva. Possibili rela-

zioni con la geodinamica Cenozoica del Mediterraneo Occiden-

tale. Boll. Soc. Geol. Ital. 114, 465–475.

Pares, J.M., van der Pluijm, B.A., Dinares-Turell, J., 1999. Evolu-

tion of magnetic fabric during incipient deformation of mu-

drocks (Pyrenees, northern Spain). Tectonophysics 307, 1–14.

Pasci, S., 1997. Tertiary transcurrent tectonics of north-central Sar-

dinia. Bull. Soc. Geol. France 168, 301–312.

Patacca, E., Sartori, R., Scandone, P., 1990. Tyrrhenian basin and

Apenninic arcs: kinematic relations since late Tortonian times.

Mem. Soc. Geol. Ital. 45, 425–451.

Rochette, P., Jackson, M., Aubourg, C., 1992. Rock magnetism and

the interpretation of anisotropy of magnetic susceptibility. Rev.

Geophys. 30 (3), 209–226.

Rossetti, F., Faccenna, C., Goffe, B., Monie, P., Argentieri, A.,

Funiciello, R., Mattei, M., 2001. Alpine structural and metamor-

phic signature of the Sila Piccola Massif nappe stack (Calabria,

Italy): insights for the tectonic evolution of the Calabrian Arc.

Tectonics 20, 112–133.

Sagnotti, L., Speranza, F., 1993. Magnetic fabric analysis of the

Plio-Pleistocene clay units of the Sant’Arcangelo basin, south-

ern Italy. Phys. Earth Planet. Inter. 77, 165–176.

Sagnotti, L., Faccenna, C., Funiciello, R., Mattei, M., 1994. Mag-

netic fabric and structural setting of Plio-Pleistocene clayey

units in an extensional regime: the Tyrrhenian margin of central

Italy. J. Struct. Geol. 16, 1243–1257.

Sagnotti, L., Speranza, F., Winkler, A., Mattei, M., Funiciello, R.,

1998. Magnetic fabric of clay sediments from the external north-

ern Apennines (Italy). Phys. Earth Planet. Inter. 105, 73–93.

Scheepers, P.J.J., Langereis, C.G., 1994. Magnetic fabric of Pleis-

tocene clays from the Tyrrhenian arc: a magnetic lineation in-

duced in the final stage of the middle Pleistocene compressive

event. Tectonics 13 (5), 1190–1200.

Selvaggi, G., Chiarabba, C., 1995. Seismicity and P-wave velocity

image of the southern Tyrrhenian subduction zone. Geophys. J.

Int. 121, 818–826.

Seranne, M., 1999. The Gulf of Lion continental margin (NW

Mediterranean) revisited by IBS: an overview. In: Durand, B.,

Mascle, A., Jolivet, L., Horvath, F., Seranne, M. (Eds.), The

Mediterranean basins: tertiary extension within the Alpine oro-

gen. Geol. Soc. London, Spec. Publ., vol. 156, pp. 21–53.

Sowerbutts, A.A., Underhill, J.R., 1998. Sedimentary response to

intra-arc extension: controls on Oligo-Miocene deposition, Sar-

cidano sub-basin, Sardinia. J. Geol. Soc. London 155, 491–508.

Speranza, F., 1999. Paleomagnetism and the Corsica–Sardinia ro-

tation: a short review. Boll. Soc. Geol. Ital. 118, 537–543.

Speranza, F., Maniscalco, R., Mattei, M., Di Stefano, A., Butler,

R.W.H., Funiciello, R., 1999. Timing and magnitude of rota-


tions in the frontal thrust system of southwestern Sicily. Tecton-

ics 18 (6), 1178–1197.

Thomas, B., Gennesseaux, M., 1986. A two stages rifting in the

basins of Corsica–Sardinia straits. Mar. Geol. 72, 225–239.

Uyeda, S., Kanamori, H., 1979. Backarc opening and the mode of

subduction. J. Geophys. Res. 84, 1049–1106.

Van der Voo, R., 1993. Paleomagnetism of the Atlantic, Thethys, and

Iapetus Oceans. Cambridge Univ. Press, Cambridge, 411 pp.

Vigliotti, L., Langenheim, V.E., 1995. When did Sardinia stop rotat-

ing? New paleomagnetic results. Terra Nova 7, 424–435.

Winkler, A., Florindo, F., Sagnotti, L., Sarti, G., 1996. Inverse to

normal magnetic fabric transition in an upper Miocene marly

sequence from Tuscany (Italy). Geophys. Res. Lett. 23 (9),

909–912.


Extensional tectonics on Sardinia (Italy): insights into the arc–back-arc transitional regime

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