The Sicily Channel, located in the foreland area of the African plate, is a very interesting geol... more The Sicily Channel, located in the foreland area of the African plate, is a very interesting geological area in the Western-Central Mediterranean, as it has undergone different tectonic processes because of its proximity to the convergence zone with the European plate. Extension and opening of a rift zone (Sicily Channel Rift Zone, including the Pantelleria, Malta, and Linosa grabens) occurred in the lower plate of the subduction zone marked by the Gela Thrust System and the Calabrian Accretionary Wedge, respectively located south and south-east of Sicily, and the Maghrebian chain to the west. We analyzed geological and geophysical data, such as variable penetration seismic reflection profiles integrated with borehole data; these allowed us to investigate subsurface structures down to the crust-mantle boundary. The crustal profile shows a Moho deepening down to 11.8 s/(TWT) under the Gela Thrust System and going up to 8 s/(TWT) under the Linosa Graben. Moreover, the presence of several hyperbolae zones and signal anomalies have been linked to a rise of deep fluids associated with mantle uplift and, upward, to magmatic intrusions. The sub-surface also shows evidence of a N-S oriented zone, from the Gela Thrust System to the Malta and Linosa grabens, which has undergone contractional tectonic events superimposed on previous extensional structures. Throughout this area, from the Early-Middle Miocene to the Early Pliocene, an extensional event occurred in association with the slab roll-back of the African Plate. In this phase, several volcanic intrusions concentrated near the grabens’ rims suggest a relation between the extension, the Moho rising, and the magmatic manifestations. Afterward, a compressional event in the Madrepore and Malta Grabens was registered. This event has been correlated to the advance of the Gela Thrust Front, which, according to literature bio-chronostratigraphic analysis, had three stages of advancement in Zanclean, Piacenzian and Chibanian. Furthermore, a recent contractional event caused the folding of the seafloor in the central part of the Malta Graben. This latter phase has been related to a potential change in the subduction polarity. These results provide new insights into the regional kinematic setting of the Sicily Channel, suggesting that strain located within the African Plate can be explained through the overlapping of both intra-plate (localized asthenospheric rise) and inter-plate (compression transmitted from surrounding mountain belts) processes ongoing between Europa and Africa. Indeed, the Sicily Channel structural setting resulted from the interplay of the rollback of the African slab, the consequent changes in the asthenospheric flow that caused extension and local magmatic intrusions, and the active subduction front and its potential polarity reversal that caused local and polyphased compressional pulses.
It has long been recognized that the central Adria Plate, as well as the Dinaric-Hellenic sector,... more It has long been recognized that the central Adria Plate, as well as the Dinaric-Hellenic sector, contains a vast volume of Triassic salt associated with diapirism and it is well know that Triassic evaporites developed in the Mediterranean Sea region over epicratonic platforms. Nearby the Apennines and Dinaric-Hellenic front, several authors highlighted the presence of Triassic salt structures such as pillows, diapirs and salt walls, mostly triggered by Neogene tectonic shortening associated with the accretion of these opposite Chains. Nevertheless, in the Apulian foreland, representing the southernmost termination of the Adria plate the Northern Ionian Sea, Triassic evaporitic deposits have never been mapped due to the lack of explorative wells in this deepwater offshore sector. Based on seismic reflection profiles, we illustrate new evidences of Triassic evaporites in the Apulian foreland subsurface associated with two squeezed diapirs as evidence of regional shortening episodes, probably enucleated from inherited Mesozoic salt structures such as pillows and/or salt domes, thus implying new constrains on the paleogeographic reconstruction of the Northern Ionian Sea. The identification of halokinetic-related sequences up to the Plio-Quaternary foreland shallow sediments allows to constrain the evolution of the two diapirs. It results that they are reactivated till Plio-Pleistocene times in response to the compressive stress trasmitted by the Southern Apennines/Calabrian Arc and Hellenides to the Apulian foreland. Later, after Middle Pleistocene, they were dismembered by extensional tectonics related to Adria plate flexuring, as they represent areas of weakness. These observations make the regional geological contest one of the foundamental features controlling the Plio-Pleistocene Triassic evaporitic squeezing in the southern Adria Plate.
We here discuss the Early Oligocene-Middle Miocene evolution of the Epiligurian wedge-top basin s... more We here discuss the Early Oligocene-Middle Miocene evolution of the Epiligurian wedge-top basin system cropping out in the middle Enza Valley (Northern Apennines, Italy). Newly acquired stratigraphic and structural data, backed up by literature review, highlight that during the Rupelian to Serravallian time span, sedimentation was controlled by a left-lateral transpressive system. This system, here named as the Enza Valley Deformation Zone (EVDZ), is SW-NE directed and trends obliquely to the main regional NW-SE-directed structural axis characterizing this part of the Northern Apennines nowadays. The syn-sedimentary activity is testified by: (1) local to regional stratigraphic unconformities, (2) lateral variations of sedimentary facies associations, (3) thickness changes of the stratigraphic units and (4) the occurrence of mass transport deposits. This study suggests that structural lineaments like the EVDZ, transversal to the main regional tectonic trends, may have played a long-term control on the syn-orogenic sedimentation atop the evolving Apennine orogen.
Papers, data, figures, maps and any other material published are covered by the copyright own by ... more Papers, data, figures, maps and any other material published are covered by the copyright own by the Società Geologica Italiana. La Società Geologica Italiana, i curatori scientifici non sono responsabili delle opinioni espresse e delle affermazioni pubblicate negli articoli: l'autore/i è/sono il/i solo/i responsabile/i.
RENDICONTI ONLINE DELLA SOCIETÀ GEOLOGICA ITALIANA, Aug 1, 2012
We analyzed the structure and evolution of the external Calabrian Arc (CA) subduction complex thr... more We analyzed the structure and evolution of the external Calabrian Arc (CA) subduction complex through an integrated geophysical approach involving multichannel and single-channel seismic data at different scales. Pre-stack depth migrated crustal-scale seismic profiles have been used to reconstruct the overall geometry of the subduction complex, i.e., depth of the basal detachment, geometry and structural style of different tectonic domains, and location and geometry of major faults. High-resolution multichannel seismic (MCS) and sub-bottom CHIRP profiles acquired in key areas during a recent cruise, as well as multibeam data, integrate deep data and constrain the fine structure of the accretionary wedge as well as the activity of individual fault strands. We identified four main morpho-structural domains in the subduction complex: 1) the post-Messinian accretionary wedge; 2) a slope terrace; 3) the pre-Messinian accretionary wedge and 4) the inner plateau. Variation of structural style and seafloor morphology in these domains are related to different tectonic processes, such as frontal accretion, out-of-sequence thrusting, underplating and complex faulting. The CA subduction complex is segmented longitudinally into two different lobes characterized by different structural style, deformation rates and basal detachment depths. They are delimited by a NW/SE deformation zone that accommodates differential movements of the Calabrian and the Peloritan portions of CA and represent a recent phase of plate reorganization in the central Mediterranean. Although shallow thrust-type seismicity along the CA is lacking, we identified active deformation of the shallowest sedimentary units at the wedge front and in the inner portions of the subduction complex. This implies that subduction could be active but aseismic or with a locked fault plane. On the other hand, if underthrusting of the African plate has stopped recently, active shortening may be accommodated through more distributed deformation. Our findings have consequences on seismic hazard, since we identified tectonic structures likely to have caused large earthquakes in the past and to be the source regions for future events.
The northern Apennines of Italy are a classical site for studying fundamental issues in tectonic ... more The northern Apennines of Italy are a classical site for studying fundamental issues in tectonic studies, such as ophiolite formation and emplacement, kinematics of thrust wedges, role of in-and out-of-sequence thrusting, and of along strike segmentation, syn-orogenic versus post-orogenic extension, interplay between tectonics, erosion and sedimentation etc. Accordingly, the northern Apennines have been extensively studied since more than two centuries ago. Despite the huge amount of available data with different resolution, a 3D comprehensive regional view combining in a modern framework all available surface and subsurface information for contiguous sectors of the chain is still lacking. We performed such an attempt in the area framed between the Taro valley to the north and the northern termination of the Alpi Apuane to the south. The region includes the main morphostructural zones of the NorthWest Apennines from the Tyrrhenian coast (SSW of La Spezia), through the main topographic divide of the Apennines, up to the foothills range of the chain to the north. The area has been investigated through a multidisciplinary approach that integrated surface geological data, collected during the last two decades of structural and stratigraphic field works, and subsurface geological data. The construction of two regional NE-SW trending cross-sections (the Levanto-Pontremoli-Parma to the north and the La Spezia-Sarzana-North Apuane-Cerreto to the south), intersected by a NW-SE trending Taro-Lunigiana-Alpi Apuane composite section, allowed us to illustrate (i) the role of out-ofsequence blind thrusting in the basement, (ii) the presence of low-angle normal faulting and its relationships with recent to active high-angle normal faulting. Both extensional and contractional systems have relevant implications for the tectonics of the northern Apennines as well as the seismotectonics of the studied region.
Mantle-derived serpentinites have been detected at magma-poor rifted margins and above subduction... more Mantle-derived serpentinites have been detected at magma-poor rifted margins and above subduction zones, where they are usually produced by fluids released from the slab to the mantle wedge. Here we show evidence of a new class of serpentinite diapirs within the external subduction system of the Calabrian Arc, derived directly from the lower plate. Mantle serpentinites rise through lithospheric faults caused by incipient rifting and the collapse of the accretionary wedge. Mantle-derived diapirism is not linked directly to subduction processes. The serpentinites, formed probably during Mesozoic Tethyan rifting, were carried below the subduction system by plate convergence; lithospheric faults driving margin segmentation act as windows through which inherited serpentinites rise to the sub-seafloor. The discovery of deep-seated seismogenic features coupled with inherited lower plate serpentinite diapirs, provides constraints on mechanisms exposing altered products of mantle peridotite ...
Reconstructing the paleofluid evolution in mature fault zones, which typically have complex struc... more Reconstructing the paleofluid evolution in mature fault zones, which typically have complex structural architectures, is a challenging task because re-activation of pre-existing deformation structures and dissolution-reprecipitation processes are very abundant. Understanding why specific structural elements are preferentially mineralized and what are the factors leading to rapid fluid migration and accumulation, bears geological and economic implications, especially in seismically active fault zones. We studied the Compione Fault on the Tyrrhenian Sea side of the Northern Apennines orogenic wedge, Italy, which is a segment of the 30 km long Northern Lunigiana high-angle extensional fault system still active today. The Compione Fault propagated from the metamorphic basement and accumulated about 1.5 km of displacement. We used structural, petrographic, isotopic, microthermometric, compositional and organic matter analyses to constrain fluid and host rock properties during fault zone evolution. This approach allowed us to quantify the thermal anomaly in the fault zone and to infer the processes responsible for such a disequilibrium. Specifically, we show that in the fault process zone ahead of the upper fault tip, which is twice as wide as the damage zone, seismic pumping caused suprahydrostatic fluid pressures and that local dilation promoted the nucleation of a highly permeable mesh of conjugate extensional shear fractures hosting calc-silicate mineralization. The thermal difference between hydrothermal minerals in the conjugate fracture mesh and the host rock is 60-90 °C. The mineralizing fluids were deeply-sourced from metamorphic reactions. Propagation of the upper fault tip caused process zone folding and incorporation into the fault damage zones. As the upper fault tip breached through shallower structural levels, it favored mixing between deep and meteoric fluids.
The Calabrian Arc is a narrow subduction-rollback system resulting from Africa/Eurasia plate conv... more The Calabrian Arc is a narrow subduction-rollback system resulting from Africa/Eurasia plate convergence. While crustal shortening is taken up in the accretionary wedge, transtensive deformation accounts for margin segmentation along transverse lithospheric faults. One of these structures is the NNW-SSE transtensive fault system connecting the Alfeo seamount and the Etna volcano (Alfeo-Etna Fault, AEF). A second, NW-SE crustal discontinuity, the Ionian Fault (IF), separates two lobes of the CA subduction complex (Western and Eastern Lobes) and impinges on the Sicilian coasts south of the Messina Straits. Analysis of multichannel seismic reflection profiles shows that: 1) the IF and the AEF are transfer crustal tectonic features bounding a complex deformation zone, which produces the downthrown of the Western lobe along a set of transtensive fault strands; 2) during Pleistocene times, transtensive faulting reactivated structural boundaries inherited from the Mesozoic
The Sicily Channel, located in the foreland area of the African plate, is a very interesting geol... more The Sicily Channel, located in the foreland area of the African plate, is a very interesting geological area in the Western-Central Mediterranean, as it has undergone different tectonic processes because of its proximity to the convergence zone with the European plate. Extension and opening of a rift zone (Sicily Channel Rift Zone, including the Pantelleria, Malta, and Linosa grabens) occurred in the lower plate of the subduction zone marked by the Gela Thrust System and the Calabrian Accretionary Wedge, respectively located south and south-east of Sicily, and the Maghrebian chain to the west. We analyzed geological and geophysical data, such as variable penetration seismic reflection profiles integrated with borehole data; these allowed us to investigate subsurface structures down to the crust-mantle boundary. The crustal profile shows a Moho deepening down to 11.8 s/(TWT) under the Gela Thrust System and going up to 8 s/(TWT) under the Linosa Graben. Moreover, the presence of several hyperbolae zones and signal anomalies have been linked to a rise of deep fluids associated with mantle uplift and, upward, to magmatic intrusions. The sub-surface also shows evidence of a N-S oriented zone, from the Gela Thrust System to the Malta and Linosa grabens, which has undergone contractional tectonic events superimposed on previous extensional structures. Throughout this area, from the Early-Middle Miocene to the Early Pliocene, an extensional event occurred in association with the slab roll-back of the African Plate. In this phase, several volcanic intrusions concentrated near the grabens’ rims suggest a relation between the extension, the Moho rising, and the magmatic manifestations. Afterward, a compressional event in the Madrepore and Malta Grabens was registered. This event has been correlated to the advance of the Gela Thrust Front, which, according to literature bio-chronostratigraphic analysis, had three stages of advancement in Zanclean, Piacenzian and Chibanian. Furthermore, a recent contractional event caused the folding of the seafloor in the central part of the Malta Graben. This latter phase has been related to a potential change in the subduction polarity. These results provide new insights into the regional kinematic setting of the Sicily Channel, suggesting that strain located within the African Plate can be explained through the overlapping of both intra-plate (localized asthenospheric rise) and inter-plate (compression transmitted from surrounding mountain belts) processes ongoing between Europa and Africa. Indeed, the Sicily Channel structural setting resulted from the interplay of the rollback of the African slab, the consequent changes in the asthenospheric flow that caused extension and local magmatic intrusions, and the active subduction front and its potential polarity reversal that caused local and polyphased compressional pulses.
It has long been recognized that the central Adria Plate, as well as the Dinaric-Hellenic sector,... more It has long been recognized that the central Adria Plate, as well as the Dinaric-Hellenic sector, contains a vast volume of Triassic salt associated with diapirism and it is well know that Triassic evaporites developed in the Mediterranean Sea region over epicratonic platforms. Nearby the Apennines and Dinaric-Hellenic front, several authors highlighted the presence of Triassic salt structures such as pillows, diapirs and salt walls, mostly triggered by Neogene tectonic shortening associated with the accretion of these opposite Chains. Nevertheless, in the Apulian foreland, representing the southernmost termination of the Adria plate the Northern Ionian Sea, Triassic evaporitic deposits have never been mapped due to the lack of explorative wells in this deepwater offshore sector. Based on seismic reflection profiles, we illustrate new evidences of Triassic evaporites in the Apulian foreland subsurface associated with two squeezed diapirs as evidence of regional shortening episodes, probably enucleated from inherited Mesozoic salt structures such as pillows and/or salt domes, thus implying new constrains on the paleogeographic reconstruction of the Northern Ionian Sea. The identification of halokinetic-related sequences up to the Plio-Quaternary foreland shallow sediments allows to constrain the evolution of the two diapirs. It results that they are reactivated till Plio-Pleistocene times in response to the compressive stress trasmitted by the Southern Apennines/Calabrian Arc and Hellenides to the Apulian foreland. Later, after Middle Pleistocene, they were dismembered by extensional tectonics related to Adria plate flexuring, as they represent areas of weakness. These observations make the regional geological contest one of the foundamental features controlling the Plio-Pleistocene Triassic evaporitic squeezing in the southern Adria Plate.
We here discuss the Early Oligocene-Middle Miocene evolution of the Epiligurian wedge-top basin s... more We here discuss the Early Oligocene-Middle Miocene evolution of the Epiligurian wedge-top basin system cropping out in the middle Enza Valley (Northern Apennines, Italy). Newly acquired stratigraphic and structural data, backed up by literature review, highlight that during the Rupelian to Serravallian time span, sedimentation was controlled by a left-lateral transpressive system. This system, here named as the Enza Valley Deformation Zone (EVDZ), is SW-NE directed and trends obliquely to the main regional NW-SE-directed structural axis characterizing this part of the Northern Apennines nowadays. The syn-sedimentary activity is testified by: (1) local to regional stratigraphic unconformities, (2) lateral variations of sedimentary facies associations, (3) thickness changes of the stratigraphic units and (4) the occurrence of mass transport deposits. This study suggests that structural lineaments like the EVDZ, transversal to the main regional tectonic trends, may have played a long-term control on the syn-orogenic sedimentation atop the evolving Apennine orogen.
Papers, data, figures, maps and any other material published are covered by the copyright own by ... more Papers, data, figures, maps and any other material published are covered by the copyright own by the Società Geologica Italiana. La Società Geologica Italiana, i curatori scientifici non sono responsabili delle opinioni espresse e delle affermazioni pubblicate negli articoli: l'autore/i è/sono il/i solo/i responsabile/i.
RENDICONTI ONLINE DELLA SOCIETÀ GEOLOGICA ITALIANA, Aug 1, 2012
We analyzed the structure and evolution of the external Calabrian Arc (CA) subduction complex thr... more We analyzed the structure and evolution of the external Calabrian Arc (CA) subduction complex through an integrated geophysical approach involving multichannel and single-channel seismic data at different scales. Pre-stack depth migrated crustal-scale seismic profiles have been used to reconstruct the overall geometry of the subduction complex, i.e., depth of the basal detachment, geometry and structural style of different tectonic domains, and location and geometry of major faults. High-resolution multichannel seismic (MCS) and sub-bottom CHIRP profiles acquired in key areas during a recent cruise, as well as multibeam data, integrate deep data and constrain the fine structure of the accretionary wedge as well as the activity of individual fault strands. We identified four main morpho-structural domains in the subduction complex: 1) the post-Messinian accretionary wedge; 2) a slope terrace; 3) the pre-Messinian accretionary wedge and 4) the inner plateau. Variation of structural style and seafloor morphology in these domains are related to different tectonic processes, such as frontal accretion, out-of-sequence thrusting, underplating and complex faulting. The CA subduction complex is segmented longitudinally into two different lobes characterized by different structural style, deformation rates and basal detachment depths. They are delimited by a NW/SE deformation zone that accommodates differential movements of the Calabrian and the Peloritan portions of CA and represent a recent phase of plate reorganization in the central Mediterranean. Although shallow thrust-type seismicity along the CA is lacking, we identified active deformation of the shallowest sedimentary units at the wedge front and in the inner portions of the subduction complex. This implies that subduction could be active but aseismic or with a locked fault plane. On the other hand, if underthrusting of the African plate has stopped recently, active shortening may be accommodated through more distributed deformation. Our findings have consequences on seismic hazard, since we identified tectonic structures likely to have caused large earthquakes in the past and to be the source regions for future events.
The northern Apennines of Italy are a classical site for studying fundamental issues in tectonic ... more The northern Apennines of Italy are a classical site for studying fundamental issues in tectonic studies, such as ophiolite formation and emplacement, kinematics of thrust wedges, role of in-and out-of-sequence thrusting, and of along strike segmentation, syn-orogenic versus post-orogenic extension, interplay between tectonics, erosion and sedimentation etc. Accordingly, the northern Apennines have been extensively studied since more than two centuries ago. Despite the huge amount of available data with different resolution, a 3D comprehensive regional view combining in a modern framework all available surface and subsurface information for contiguous sectors of the chain is still lacking. We performed such an attempt in the area framed between the Taro valley to the north and the northern termination of the Alpi Apuane to the south. The region includes the main morphostructural zones of the NorthWest Apennines from the Tyrrhenian coast (SSW of La Spezia), through the main topographic divide of the Apennines, up to the foothills range of the chain to the north. The area has been investigated through a multidisciplinary approach that integrated surface geological data, collected during the last two decades of structural and stratigraphic field works, and subsurface geological data. The construction of two regional NE-SW trending cross-sections (the Levanto-Pontremoli-Parma to the north and the La Spezia-Sarzana-North Apuane-Cerreto to the south), intersected by a NW-SE trending Taro-Lunigiana-Alpi Apuane composite section, allowed us to illustrate (i) the role of out-ofsequence blind thrusting in the basement, (ii) the presence of low-angle normal faulting and its relationships with recent to active high-angle normal faulting. Both extensional and contractional systems have relevant implications for the tectonics of the northern Apennines as well as the seismotectonics of the studied region.
Mantle-derived serpentinites have been detected at magma-poor rifted margins and above subduction... more Mantle-derived serpentinites have been detected at magma-poor rifted margins and above subduction zones, where they are usually produced by fluids released from the slab to the mantle wedge. Here we show evidence of a new class of serpentinite diapirs within the external subduction system of the Calabrian Arc, derived directly from the lower plate. Mantle serpentinites rise through lithospheric faults caused by incipient rifting and the collapse of the accretionary wedge. Mantle-derived diapirism is not linked directly to subduction processes. The serpentinites, formed probably during Mesozoic Tethyan rifting, were carried below the subduction system by plate convergence; lithospheric faults driving margin segmentation act as windows through which inherited serpentinites rise to the sub-seafloor. The discovery of deep-seated seismogenic features coupled with inherited lower plate serpentinite diapirs, provides constraints on mechanisms exposing altered products of mantle peridotite ...
Reconstructing the paleofluid evolution in mature fault zones, which typically have complex struc... more Reconstructing the paleofluid evolution in mature fault zones, which typically have complex structural architectures, is a challenging task because re-activation of pre-existing deformation structures and dissolution-reprecipitation processes are very abundant. Understanding why specific structural elements are preferentially mineralized and what are the factors leading to rapid fluid migration and accumulation, bears geological and economic implications, especially in seismically active fault zones. We studied the Compione Fault on the Tyrrhenian Sea side of the Northern Apennines orogenic wedge, Italy, which is a segment of the 30 km long Northern Lunigiana high-angle extensional fault system still active today. The Compione Fault propagated from the metamorphic basement and accumulated about 1.5 km of displacement. We used structural, petrographic, isotopic, microthermometric, compositional and organic matter analyses to constrain fluid and host rock properties during fault zone evolution. This approach allowed us to quantify the thermal anomaly in the fault zone and to infer the processes responsible for such a disequilibrium. Specifically, we show that in the fault process zone ahead of the upper fault tip, which is twice as wide as the damage zone, seismic pumping caused suprahydrostatic fluid pressures and that local dilation promoted the nucleation of a highly permeable mesh of conjugate extensional shear fractures hosting calc-silicate mineralization. The thermal difference between hydrothermal minerals in the conjugate fracture mesh and the host rock is 60-90 °C. The mineralizing fluids were deeply-sourced from metamorphic reactions. Propagation of the upper fault tip caused process zone folding and incorporation into the fault damage zones. As the upper fault tip breached through shallower structural levels, it favored mixing between deep and meteoric fluids.
The Calabrian Arc is a narrow subduction-rollback system resulting from Africa/Eurasia plate conv... more The Calabrian Arc is a narrow subduction-rollback system resulting from Africa/Eurasia plate convergence. While crustal shortening is taken up in the accretionary wedge, transtensive deformation accounts for margin segmentation along transverse lithospheric faults. One of these structures is the NNW-SSE transtensive fault system connecting the Alfeo seamount and the Etna volcano (Alfeo-Etna Fault, AEF). A second, NW-SE crustal discontinuity, the Ionian Fault (IF), separates two lobes of the CA subduction complex (Western and Eastern Lobes) and impinges on the Sicilian coasts south of the Messina Straits. Analysis of multichannel seismic reflection profiles shows that: 1) the IF and the AEF are transfer crustal tectonic features bounding a complex deformation zone, which produces the downthrown of the Western lobe along a set of transtensive fault strands; 2) during Pleistocene times, transtensive faulting reactivated structural boundaries inherited from the Mesozoic
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