Mud volcanoes along the inner deformation front of the Calabrian

Rend. Online Soc. Geol. It., Vol. 21 (2012), pp. 238-240, 3 figs.
© Società Geologica Italiana, Roma 2012
Mud volcanoes along the inner deformation front of the Calabrian
Arc accretionary wedge (Ionian Sea)
GIULIANA PANIERI (*), ALINA POLONIA (*), RENATA GIULIA LUCCHI (**) & LUIGI TORELLI (°)
Key words: Accretionary wedge, Calabrian Arc, mud
volcano, mud breccia, fluid emissions.
occurrence and nature of mud volcanism in the CA and
study the relationships between mud volcanism, fluid flow
and tectonics in the inner domains of the subduction
complex.
INTRODUCTION AND GEOLOGICAL SETTING
The Calabrian Arc (CA) is part of the eastward migrating
Apennine subduction system and represents the
Africa/Eurasia plate boundary in the Ionaina Sea. The
external part of the arc (Figure 1) is represented by a
subduction complex that reaches both the Ionian abyssal
plain and the Mediterranean Ridge and is bordered by two
major structural features, the Malta escarpment to the
southwest and the Apulia escarpment to the northeast.
The convergence between the Africa and Eurasia plates,
has generated a 10-km thick accretionary wedge in the
Calabrian Arc (CA) subduction complex due to offscraping
of the thick sedimentary section resting on the lower African
plate.
Compared with the Mediterranean Ridge, from which
wealth of data have been collected, the Calabria Arc in the
Ionian Sea has been less intensively investigated in the past.
Evidences of allochthonous material were reported by Rossi
and Sartori (1981) and Barbieri et al. (1982) who interpreted
the chaotic deposits as the result of mass flows
accompanying and/or following underthrusting of
unconsolidated sediments. The presence of mud volcanoes
were suspected few years later by Fusi and Kanyon (1996)
and Sartori (2003). Only recently, Praeg et al. (2009),
reported a province of mud volcanoes (“Madonna dello
Ionio” and “Pythagoras”) in the inner accretionary prism of
the Calabrian Arc while topographic mounds in the inner
plateau offshore the Squillace basin have been related to salt
diapirism and/or argilokinetic processes (Polonia et al.,
2011).
The aim of this study is to gain new insights on the
Fig. 1 – Tectonic map of the Calabrian Arc subduction complex (modified
form Polonia et al., 2011) with the study area.
METHODOLOGY
A multidisciplinary approach involving the analysis of
geophysical data at different resolutions and targeted ground
truthing has been used to unravel fluid flow processes and
the interplay between tectonics and mud volcanism in the
submerged portion of the Calabrian Arc.
The regional architecture of the accretionary complex
(Figure 1) was reconstructed from multichannel seismic data
(the CNR-ENI Deep Crust Seismic Profiles - CROP and
Mediterranean Sea - MS datasets). High-resolution Sparker
and sub-bottom CHIRP profiles, as well as multibeam data,
integrate deep data and constrain the fine structure of the
accretionary wedge as well as the geometry and seismic
facies of topographyc mounds in key areas.
_________________________
(*) ISMAR, Istituto di Scienze Marine, CNR, Bologna, Italy.
(**)Istituto Nazionale di Oceanografia e Geofisica Sperimentale (OGS),
Trieste, Italy.
(°) Dipartimento di Fisica e Scienze della Terra, Università di Parma,
Italy.
238
86° CONGRESSO SOCIETÀ GEOLOGICA ITALIANA
18-20 SETTEMBRE 2012, ARCAVACATA DI RENDE (CS)
Two gravity cores collected during 80’s (BARBIERI et
alii, 1982; MORLOTTI et alii, 1982) and core CALA 21
acquired ontop of a topographic swell imaged on Sparker
line J-22 (Fig. 2) were studied through micropaleontological,
sedimentological, mineralogical and stable isotope
geochemical analysis.
The sedimentological and geochemical analyses on a
newly acquired core (CALA 21) collected from the summit
of a topographic high of the inner accretionary wedge
suggest the presence of mud breccia patchy/cloudy facies
(Fig. 3) (sensu CITA et alii, 1996 and STAFFINI et alii, 1993)
where sediment disturbance is caused by fluid expulsion.
The mud breccia patchy/cloudy is characterized by silty-clay
bulk sediments containing irregularly clustered intervals of
differently coloured sediments (from dark grey to olive grey
clouds and light grey to grey matrix) with several
fragmented and vertically dislocated thin sandy/silty
turbidites and tephra layers.
RESULTS
The integration of sediment cores analysis with
geophysical data permitted to relate tectonic activity and
different fluid emissions dynamic in mud volcanoes.
Sediment facies description, micropaleontological and stable
isotope investigations allowed to distinguish the massive
mud breccia facies within two previously collected cores (5
BS81/II and 10 BS81/II; BARBIERI et alii, 1982; MORLOTTI
et alii, 1982). The massive facies is formed by a mixture of
differently aged rock fragments (from Cretaceus to Late
Miocene, Fig. 3) deriving from deeper stratigraphic intervals
that have been mechanically incorporated into a stiff mud
matrix by powerful fluid espulsion associated to dynimic of
the the accrectionary complex. Clasts include calcareous
mudstone (light gray, firm, massive, with sometimes
abundant mica, and rounded shape), fossiliferous micrite
(light gray, firm, massive, rounded or angular in shape) with
occasionally orange-colored altered surfaces.
Fig. 3 – Examples of mud volcanoes products in the Calabrian Arc.
Massive mud breccia, with clasts found cores 5 BS81/II and 10 BS81/II.
Patchu-cloudy mud breccia observed in CALA 21 at different stratigraphic
intervals. Dotted line indicate vertical migration structures. Disrupted
tephra/terrigenous sandy layers and micro-pipes filled with silt/fine sand
transported by fluid escape are evident.
The integration of the entire data set provide information
on the formation of mud volcanoes in the accretionary prism
where overpressure provided by the Pliocene and
Pleistocene sediment accumulation and the evolution of
normal fault systems, triggered the fluid circulation and mud
volcanoes formation that progressively developed toward
the upper slope.
The occurrence of mud volcanic processes appears to be
related to major structural features, such as the inner
deformation front of the CA subduction complex, a
transpressive fault accommodating strain partitioning at the
contact between the highly deformed wedge and the
continental basement. The lack of evaporitic impermeable
cap in the inner wedge, active faulting along the inner
deformation front and transverse structures segmenting the
subduction complex all favor rising of fluids from the wedge
interior and formation of diapiric features.
Fig. 2 – a: segment of Sparker seismic profile J-22 parallel to the Calabrian
continental margin across the transition between the inner plateau and the
inner accretionary wedge. The boundary between the two structural
domains corresponds to the splay-3 fault system. The three studied cores
are located at the footwall and hangingwall of this major tectonic feature. b:
zoom of the seismic line across the mud volcano. c: contour bathymetric
map of the study area superimposed on the slope map of the multibeam data
(isolines every 200m).
239
86° CONGRESSO SOCIETÀ GEOLOGICA ITALIANA
18-20 SETTEMBRE 2012, ARCAVACATA DI RENDE (CS)
REFERENCES
POLONIA A., TORELLI L., MUSSONI P., GASPERINI L.,
ARTONI A., & D. KLAESCHEN (2011) - The Calabrian
Arc subduction complex in the Ionian Sea: regional
architecture, active deformation and seismic hazard.
Tectonics 30, TC5018.
PRAEG D., CERAMICOLA S., BARBIERI R., UNNITHAN V., &
WARDELL N. (2009) - Tectonically-driven mud
volcanism since the late Pliocene on the Calabrian
accretionary prism, central Mediterranean Sea. Mar.
and Petr. Geol., 26, 1849-1865.
STAFFINI F., SPEZZAFERRI S., & AGHIB F. (1993) - Mud
diapirs of the Mediterranean Ridge: sedimentological
and micropaleontological study of the mud breccia. Riv.
It. Paleont. Strat. 99, 225–254.
BARBIERI F., MORLOTTI E., POERIO L., RAFFI I., &TORELLI
L. (1982) - Dati geologici preliminari sul bacino di
Crotone-Spartivento (Mar Ionio). Acta Nat. de l’At
Parm. 18, 141-155.
CITA M.B., ERBA E., LUCCHI R., POTT M., VAN DER MEEER
R., & NIETO L. (1996) - Stratigraphy and sedimentation
in the Mediterranean Ridge diapiric belt. Mar. Geol. 132,
131- 150.
MORLOTTI E., SARTORI R., TORELLI L., BARBIERI F., &
RAFFI I. (1982) - Chaotic deposits from the external
Calabrian Arc (Ionian Sea, eastern Mediterranean).
Mem. Soc. Geol. It. 24, 261–275.
240

Download Report