Evidences of post‐rift compressional tectonics in the North‐Eastern Tyrrhenian Basin.Marco Pastore (1), Giovanni Pezzati (2), Filippo D’Oriano (1), Paola Vannucchi (2), Vincenzo Picotti (1) and Nevio Zitellini (3)

(1) Dipartimento di Scienze della Terra, Università di Bologna, Bologna, Italy., (2) Dipartimento di Scienze della Terra, Università di Firenze, Firenze, Italy., (3) ISMAR CNR, Bologna, Italy.

Session: TS6.1/G3.3/GD5.4/SM1.5 ‐ Poster: EGU2011‐8170

Corresp. e‐mail: marco.pastore71@email.it

Line drawing of lines AC38 and AC48,

collected in the Palmarola basin.

The whole sedimentary package is

splitted into two main sequences, A and

B, respectively above and below the “R”

unconformity. See section F for location

(Fig. 7 and 8) and explanation.

LINE AC38 (Fig. 2):

Palmarola basin (landwarth) and

Palmarola high are here showed.

We suggest that two transpressional

faults (fix 15 and 12) have here

reactivated old syn‐rift normal faults,

and that the main compressional event

is marked by the "R" unconformity. On

the high that border the basin (fix

12‐14), uplift appears still active.

LINE AC48 (Fig. 3):

Saddle between two sub‐basins in the

Palmarola basin, with an axis trending

SW‐NE.

The folding of the reflectors under "R"

suggests a reactivation of the previous

syn‐rift faults. This uplift seems not

active now, because sedimentation in

level A is just slightly bend and shows

progressives onlaps just near the

unconformity and not in more recents

reflectors.

Fig. 2: line drawing of the AC38 seismic

profile (Active compressional tectonic).

Fig. 3: line drawing of the AC48 seismic

profile (Inactive compressional tectonic).

AC38

AC48

EVIDENCES OF COMPRESSIONAL TECTONICSC

Legend:

Normal Fault Inverse Fault

Z

"Z" unconformity

(basement)

(Marani et al., 1986)

R

"R" unconformity

(syn ‐ compression)

(Marani and Zitellini, 1986)

Acoustic

sea floor

A

B

Mostly post‐compressional sediment thickness

and displacement (isochronopaches TWT).

Mostly pre‐syn‐compressional sediment thickness

and displacement (isochronopaches TWT).

Ponza isl.Palmarola isl.

Circeo

cape

Sabaudia (LT)

Ponza isl.Palmarola isl.

Sabaudia (LT)

Circeo

cape

Fig. 7: thickness (isochronopaches TWT), sediment distribution and pre‐compressional

tectonic in the Palmarola basin and ridge area.

Fig. 8: thickness (isochronopaches TWT), sediment distribution and syn‐post

compressional tectonic in the Palmarola basin and ridge area.

F INVERSION TECTONICS IN THE PALMAROLA BASIN

Palmarola Ridge Palmarola Ridge

A major unconformity "R" (after Marani and Zitellini, 1986) drawn in the Palmarola basin and ridge, give us the possibility to map the sediment thickness in that area before (Fig. 7) and after it (Fig. 8).

As shown in section C, this "R" marks the main compressional event occurred in this area.

Before "R" (FIg 7) Palmarola basin is not well formed, althoug Palmarola ridge is recognizeable (low sediment are here deposited). Depocenter is located landwarth and filled with sedimens mainly related

to progradation. A saddle between Palmarola ridge and the "H1" structural high shows high sediment thickness.

After "R" (Fig. 8), depocenters are migrated into the Palmarola basin, which is now well recognizeable, and low sediment thickness are present on the saddle previously described.

These changes suggest an uplift of the basement in the northern part of Palmarola ridge and in the saddle: faults bounding the basin are reactivated in compression.

H1 high

8 ms

125 ms

250 ms

375 ms

625 ms

750 ms

500 ms

875 ms

1000 ms

TWTTWT

12 ms

50 ms

100 ms

150 ms

200 ms

250 ms

300 ms

400 ms

450 ms

500 ms

350 ms

LINE AC10 (Fig. 4):

Intraslope basin with a semigraben

structure generated by a normal fault

acting during syn‐rift extensional

tectonic.

Sediments show a wedging feature to

the right, where is located the

depocenter (fix 12).

However, sediments close to the normal

fault are folded and displaced upwards

forming a large anticline.

A reactivation of the previous normal

fault by a compression with sigma‐1

almost parallel to the rifting structure is

here suggested.

Fig. 4: line drawing of the AC10 seismic profile (Syn‐Rif normal fault reactivated as inverse fault).

AC10

D REACTIVATION OF EXTENSIONAL TECTONIC

Fig. 5: isochrones TWT of the "Z" unconformity (beological basement) and location of AC10, AC38

and AC48 seismic lines described in section C. Red square: area analyzed in section F.

Fig. 6: thickness of the plio‐quaternary sedimentation (isochronopaches TWT), and

actual tectonics in the study area.

E BASEMENT MORPHOLOGY AND SEDIMENT THICKNESS IN THE STUDY AREA

Monte Argentari

Palmarola ridge and basin area

Fig. 5: the basement map shows an upper continental slope interrupted by intraslope basins, and followed (to the west) by structural hights that border these peri‐tyrrhenian basins. The axes of positive and

negative structures are mainly oriented NW‐SE, in agreement with the local direction of the Tirrhenian rift.

Fig. 6: in the northern part of the study area the sedimentation is mainly controlled by the basement morphology, whereas in the southern‐west part this relationship is less evident. Sediment thickness above

1000 ms TWT are detected near the coast betw. Anzio and Capo Circeo, west to the Tiber mouth and south to Monte Argentario.

From Monte Argentario to Tiber mouth the main tectonics is related to extensions.

Further south we found inverted structures, both active and inactive, the main of them

are recognized along the structural high that forms the Palmarola ridge.

An enlargement of this area (see red box in Fig. 5) shown in section F, higlights the relation

between the faults systems.

40 ms

250 ms

500 ms

750 ms

1000 ms

1250 ms

TWT200 ms

1000 ms

500 ms

1500 ms

2000 ms

2500 ms

3000 ms

3500 ms

4000 ms

TWT

Inactive normal fault

Active normal fault

Active anticlinal axis

Inactive anticlinal axis

Inactive sinclinal axis

Active sinclinal axis

Active reverse fault

Inactive reverse fault

Isochrones/Isochronopaches

Coastline

Legend:

Fig. 9: active and inactive tectonics found in the study area.

G CONCLUSIONS

A grid of seismic lines in the north‐eastern coast of the Tyrrhenian are analyzed here. As expected, the structural

grain is dominated by syn‐rift extensional faults (most of them appear inactive), tilted blocks and intraslope

basins oriented mainly NW‐SE.

We found evidences of tectonic inversion mainly in the southern part, around the Palmarola ridge and basin.

We recognized in this area a major unconformity "R" that marks the main phase of the compressional event

occurred here. Evidences of ridge uplift with evident migration of depocenter are also present (see section F).

Seismic reflectors, related to progradational sequences are here involved in the intraslope ridge uplift. This give

us a constrain for the age of the beginning of the compressional inversion, which should be younger than the

beginning of the progradation in this area, i.e. 1.5 Ma (Marani et al 1986).

We also found in some areas folded reflectors till the seabed, suggesting that compressions and uplift are still

active.

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The Tyrrhenian Sea lies in the Mediterranean Sea between Corsica, Sardinia, Sicily and the

Italian Peninsula. It is characterized by a triangular shape and in the area south of the Ponza

Island it is deeper than 3600m.

The Tyrrhenian basin can be subdivided in two main sectors: The Northern Tyrrhenian Sea and

The Southern Tyrrhenian Sea. The two parts of the basin are separated along the 41°N parallel,

where is present a strong magnetic lineation (e.g. Bolis et al., 1981; Finetti and Del Ben, 1986).

The widely accepted model consider the Tyrrhenian Sea as a small back arc basin, connected to

the African (Adria‐Ionian) subducting plate (e.g. Malinverno and Ryan, 1986; Faccenna et al.,

2001a, 2001b), which formation occurred in a compressional framework due to the convergence

between Africa and Eurasia plates.

The Tyrrhenian started to form in the Upper Miocene (10 Ma) (Kastens and Mascle, 1990;

Sartori et al., 2001). Afterwards, the extension migrated to the south‐east, with the formation of

the Vavilov and the Marsili Plain in the Plio‐Pleistocene (Kaestens et al, 1998). The Northern

Tyrrhenian stopped opening in the late Miocene (6‐5 Ma) and active deformation migrated

south‐eastward (Malinverno and Ryan, 1986; Kastens et al., 1988.).

The magmatic activity, ascribed to the extensional processes, points out the migration of the

extension. In the Northern Tyrrhenian Sea, the oldest (15‐13,5 Ma) magmatic event has been

recognized in the Sisco outcrop in the north‐eastern area of Corsica. Eastward, the magmatism is

progressively younger and the youngest events are registered in the Tuscan‐Latial area where

are present the Cimini and Vulsini mountains, the Amiata mount and Larderello (1,2‐0,1 Ma)

(e.g. Civetta et al., 1978; Rocchi et al., 2002).

In the Southern Tyrrhenian, the migration of the extension is associated to the formation of the

Vavilov and to the Marsili volcanoes in the Quaternary (Savelli, 1988; Savelli, 2002).

One of the main characteristic of the Thirrenian passive margin is the presence of “peri‐

tyrrhenian basins” (first described by Selli and Fabbri, 1971), located along the continental slope

of the whole Tyrrhenian basin, separating it in “upper” and “lower”, and where a large amount

of sediments are trapped into.

These basins, formed mainly by syn‐rift extensional tectonic, give us the possibility to recognize

in their sediments the record of deformations occurred after the rift.

In this work we analyzed about 1600 miles of

high‐resolution, near vertical incidence, seismic

profiles collected by ISMAR‐BO during the 80’s

between Monte Argentario (Tuscan Archipelago)

and Cape Circeo (Pontine Islands) in the North‐

Eastern Tyrrhenian basin, supplemented with

about 150 miles of multichannel seismic lines,

collected by AGIP in 1968 and available through

the Italian VIDEPI ministerial project.

We mapped the geological basement, the

sediment thickness and distribution, and their

deformations, in order to understand the syn‐

and post‐rift tectonics, with particular attention

to those deformation structures involving the

post‐rift sequences.

Evidences of “syn‐rift” faults associated to tilted

blocks and basin formation with prevailing

direction NW‐SE are present in the whole area,

but, particularly in the southern part, we found

also anticline and syncline systems trending

approximately parallel to the basement

extensional structures.

Fig. 1: shaded relief of the tyrrhenian sea (data from Marani et al., 2004 and GEBCO) and geological

sketch map of central Italy (modified after Carta Strutturale d’Italia, 1981 ).

Red box: study area; bathymetric and topographic contour interval: 1000m.

A INTRODUCTION B THE TYRRHENIAN SEA

Rome