Andrea Billi - Academia.edu (original) (raw)
Papers by Andrea Billi
Journal of Structural Geology, 2016
Journal of the Geological Society, 2003
Bulletin De La Societe Geologique De France, 2011
Geophysical Research Letters, 2008
Journal of Structural Geology, 2003
We studied the nucleation and growth of cataclastic fault cores from fractured damage zones in ex... more We studied the nucleation and growth of cataclastic fault cores from fractured damage zones in extensional and strike-slip fault zones in carbonate rocks. Analysed fault zones have similar protolith lithology and sedimentary fabric, but different geometry, kinematics, size, tectonic environment and deformation history. Orthorhombic rock lithons, a few decimetres in size, characterise the structural fabric of damage zones. Lithons derive from the intersection of a dominant fracture/cleavage set with bedding and/or joints. At the damage zone-fault core transition, orthorhombic lithons reduce in size and approach an isometric shape. Their cross-sectional aspect ratio has an average value of 1.4. Analysed fault cores have similar rock textures, sorting and comminution degree. Particle-size distributions of fault core rocks show linear trends in log-log graphs and average fractal dimension of 2.5. Our results on rock fabrics suggest that fault core development initiates from rock masses in damage zones, where the shape anisotropy of orthorhombic lithons favours additional fracturing at high angle to their long axes. Eventually, smaller, nearly isometric lithons generate from repeated fracturing of orthorhombic lithons. When the aspect ratio of these lithons approaches the threshold value of about 1.4, particle rotation is favoured and cataclastic flow starts. Owing to the granular nature of the damage zone-fault core transitions in carbonate rocks, analogies with the nucleation of deformation bands in sandstones can be established. Our results may be of use to the industry for quantitative characterisation of fault zone permeability. According to the proposed model, radical changes on the permeability properties are expected during the growth of fault cores.
ABSTRACT Thrust fault-related folds in carbonate rocks are characterized by deformation accommoda... more ABSTRACT Thrust fault-related folds in carbonate rocks are characterized by deformation accommodated by different kinds of structures, such as joints, faults, pressure solution seams (PSSs), and deformation bands, which may form at various stages during the folding process. Defining the distribution, orientation, and the type of fold-related structures and understanding the relationships between folding and fracturing is significant both for theoretical and practical purposes. Furthermore, as the deformation related to the folding process influences fluid flow through rocks, identifying the types of structures formed during folding is as important as predicting their geometries. To unravel the relationship between mechanical stratigraphy and folding process, the well-exposed Cingoli anticline (Northern Apennines), has been studied in detail. The Upper Cretaceous-Middle Eocene stratigraphy of the Cingoli anticline is characterized by a pelagic multilayer made up of fine-grained pelagic limestones and, marly limestones, in places alternated with thin continuous chert layers. The presence of several outcrops located in different structural positions of the anticline makes the Cingoli anticline an excellent natural laboratory to investigate relationships between folding, fracturing, and mechanical stratigraphy relative to the structural setting of the fold. The field data collected show that high angle to bedding PSSs, which formed before tilting and during the first stage of folding, are not homogeneously distributed in the pelagic limestones. Generally, high angle to bedding PSSs form in the marly pelagic limestones and they have been observed in several outcrops and in different structural positions except where the marly limestones are inter-bedded with stiffer chert layers. In order to analyse theoretically what observed in the field, we compared the deformation of limestones and chert layers with the deformation acting on fiber composites. In the mechanics of materials, composites refer to a matrix reinforced with particles, fibers, or laminae. During the early stage of folding, when the compressive stress is almost bedding parallel, chert layers act as a stiff lamina embedded in a weak limestone matrix. As a result, the stress is partitioned and the chert layers bear the greatest stress. Considering the mechanical properties (Poisson and Young's modulus) of the two materials (chert and limestone), and the estimated tectonic stress acting at the onset of the folding process, the stress magnitude in the limestone beds does not reach the expected value for the onset of pressure solution. For this reason, pelagic limestones containing chert layers are mainly characterized by joints whereas PSSs form in pelagic limestones without the stiffer phase (chert). This study suggests that within the same fold, and even within the same formation, different mechanical units can be characterized by different fractures types and fluid flow behaviour as a result of mechanical stratigraphy distribution.
Tectonophysics, 2016
A giant carbonate vein (≥50 m thick; fissure ridge travertines) and nearby travertine plateaus in... more A giant carbonate vein (≥50 m thick; fissure ridge travertines) and nearby travertine plateaus in the Semproniano area (Mt. Amiata geothermal field, southern Tuscany, Italy) are investigated through a multidisciplinary approach, including field and laboratory geochemical analyses (U/Th geochronology, C, Nd, O and Sr isotope systematics, REE abundances, and fluid inclusion microthermometry). The main aim of this work is to understand: (1) modes and rates for the growth of the giant vein and nearby travertine deposits within a Quaternary volcano-tectonic domain; (2) implications in terms of the CO 2 leakage; and (3) possible relationships with Quaternary paleoclimate and hydrological oscillations. Results show that the giant vein was the inner portion of a large fissure ridge travertine and grew asymmetrically and ataxially through repeated shallow fluid injections between N650 and 85 ka, with growth rates in the 10 −2 –10 −3 mm/a order. The giant vein developed mainly during warm humid (interglacial) periods, partially overlapping with the growth of nearby travertine plateaus. Estimated values of CO 2 leakage connected with the vein precipitation are between about 5 × 10 6 and 3 × 10 7 mol a −1 km − 2 , approximately representing one millionth of the present global CO 2 leakage from volcanic areas. Temperature estimates obtained from O-isotopes and fluid inclusion microthermometry indicate epithermal conditions (90–50 °C) for the circulating fluid during the giant vein growth, with only slight evidence of cooling with time. Geochemical and isotope data document that the travertine deposits formed mainly during Pleistocene warm humid periods, within a tectonically-controlled convective fluid circuit fed by meteoric infiltration and maintained by the regional geothermal anomaly hosted by the carbonate reservoir of the Mt. Amiata field.
Asbestos-bearing rock sequences constitute a remarkable natural hazard that poses important threa... more Asbestos-bearing rock sequences constitute a remarkable natural hazard that poses important threat to human health and may be at the origin of diseases such as asbestosis, mesothelioma and lung cancer). Presently, asbestos is classified as Category 1 carcinogen by world health authorities. Although regulatory agencies in many countries prohibit or restrict the use of asbestos, and discipline the environmental asbestos exposure, the impact of asbestos on human life still constitutes a major problem. Naturally occurring asbestos includes serpentine and amphibole minerals characterised by fibrous morphology and it is a constituent of mineralogical associations typical of mafic and ultramafic rocks within the ophiolitic sequences. Release of fibres can occur both through natural processes (erosion) and through human activities requiring fragmentation of ophiolite rocks (quarrying, tunnelling, railways construction, etc.). As a consequence, vulnerability is increasing in sites where workers and living people are involved by dispersion of fibres during mining and milling of ophiolitic rocks. By analysing in the field different exposures of ophiolitic sequences from the Italian peninsula and after an extensive review of the existing literature, we remark the importance of the geological context (origin, tectonic and deformation history) of ophiolites as a first-order parameter in evaluating the asbestos hazard. Integrated structural, textural, mineralogical and petrological studies significantly improve our understanding of the mechanisms governing the nucleation/growth of fibrous minerals in deformation structures (both ductile and brittle) within the ophiolitic rocks. A primary role is recognised in the structural processes favouring the fibrous mineralization, with correlation existing between the fibrous parameters (such as mineralogical composition, texture, mechanics characteristics) and the particles released in the air (such as shape, size, and amount liberated during rock fragmentation). Accordingly, we are confident that definition of an analytical protocol based on the geological attributes of the asbestos-bearing rocks may constitute a propaedeutical tool to evaluate the asbestos hazard in natural environments. This approach may have important implications for mitigation effects of the asbestos hazard from the medical field to the engineering operations.
We describe the evolution of the deformation pattern at Etna in the July-August 2001 eruption. Se... more We describe the evolution of the deformation pattern at Etna in the July-August 2001 eruption. Seismicity started the 13th of July and ground deformations culminated the 16th, developing of a N-S graben ~500 m wide and ~1 m deep at Montagnola (~3 km south of the summit craters). Contemporaneously, the 16th, the eruption started from the summit crater, where it
Geomorphology, 2016
Sinkholes and other karst structures in settled carbonate lands can be a significant source of ha... more Sinkholes and other karst structures in settled carbonate lands can be a significant source of hazard for humans and human works. Acque Albule, the study area of this work, is a Plio-Pleistocene basin near Rome, central Italy, superficially filled by a large and thick deposit of late Pleistocene thermogene travertine. Human activities blanket large portions of the flat territory covering most evidence from geological surface processes and potentially inducing scientists and public officials to underestimate some natural hazards including those connected with sinkholes. To contribute to the proper assessment of these hazards, a geomorphologic study of the basin was performed using digital elevation models (DEMs), recent aerial photographs, and field surveys. Historical material such as old aerial photographs and past geomorphologic studies both pre-dating the most part of quarrying and village building was also used together with memories of the elderly population. This preliminary study pointed out the presence of numerous potentially active sinkholes that are at present largely masked by either quarrying or overbuilding. Where this first study pointed out the apparent absence of sinkholes in areas characterized by high density of buildings, a detailed subsurface study was performed using properly-calibrated electrical resistivity tomography (ERT) and dynamic penetration measurements (DPSH), together with some borehole logs made available from the local municipality. This second study highlighted the presence of sinkholes and caves that are, this time, substantially hidden to the resolution of standard methods and materials such as aerial photographs, DEMs, and field surveys. Active sinkhole subsidence in the Acque Albule Basin may explain, at least in part, the frequent damages that affect numerous buildings in the area. The main conclusion from this study is that the mitigation of sinkhole hazard in highly populated areas has to pass through a thorough search of (hidden) sinkholes that can be masked by the Anthropocenic molding and blanketing of the territory. For these purposes, data from historical (pre-Anthropocene) documents as well as, where possible, subsurface investigations are fundamental.
Bollettino Societa Geologica Italiana, 2000
... il criterio dei rolax trattato in Salvini & Vittori (1982) ed è slato realizzalo auto... more ... il criterio dei rolax trattato in Salvini & Vittori (1982) ed è slato realizzalo automaticamente con l'ausilio del software DAISY 2.6 (Salvini ... dissoluzione (Pantano S. Egidio, Faglia di Mattinata), b) Faglia inversa con superfici di clivaggio al letto (S. Marco in Lamis, ramo transpressivo ...
The evolution of fracturing and cataclasis influences the mechanical and permeability properties ... more The evolution of fracturing and cataclasis influences the mechanical and permeability properties of fault zones. Fault zones can behave as strong or weak mechanical discontinuities and as conduits or barriers to fluid flow mainly depending on the nature and amount of cataclastic rocks that developed in their cores. Our structural investigations in fault zones affecting carbonate platform rocks in the Apennines, Italy, allow us to propose an evolutionary model for the progressive development of cataclastic fault core rocks from damage zones, and for the progression of cataclasis in fault cores. Analyses of particle size in the cataclastic rocks show power law distributions with fractal dimensions spanning over a broad range. This suggests that the idea of a persistent fragmentation mechanism (self-similar cataclasis) for describing the entire evolution of natural cataclastic fault cores in carbonate rocks is inadequate. Self-similar evolution for the cataclastic process is a concept mainly derived from laboratory experiments and micromechanical modelling. Conversely, we propose that the fragmentation mechanism progressively changes with the intensity of comminution. Slip localisation within narrow shear bands is favoured when a favourable cataclastic fabric with fractal dimensions D ˜ 2.6-2.7 is achieved in the fault zone. Intense comminution in the narrow shear zones produces the preferential formation of small diameter particles resulting in particle size distributions characterised by D-values approaching or exceeding 3. The progression pathway of fracturing in damage zones and the non self-similar evolution of cataclasis in fault rocks have an important impact on the frictional and permeability properties of fault zones.
The Central Apennine are one of the most seismically active regions in the Mediterranean area and... more The Central Apennine are one of the most seismically active regions in the Mediterranean area and is affected by moderate to large shallow earthquakes that enucleate in and propagate through carbonate rocks. In this work we present a detailed fieldwork and microstructural analysis to define the architecture and deformation mechanisms of an exhumed fault zone in carbonates, the Tre Monti fault, at the northern boundary of the Fucino Basin. Fault rocks assemblages show differences in deformation mechanisms between the main and external fault planes, and subsidiary fault planes developed within the damage zone. We infer that this variety of fault rocks represents different deformation processes acting during different stages of fault development and fluid circulation. The multidisciplinary but field-based study of fault surfaces and fault rocks is fundamental to reveal the geological record of past earthquakes and seismic cycles and is strongly complementary to the seismological-based ...
ABSTRACT Thrust fault-related folds in carbonate rocks are characterized by deformation accommoda... more ABSTRACT Thrust fault-related folds in carbonate rocks are characterized by deformation accommodated by different kinds of structures, such as joints, faults, pressure solution seams (PSSs), and deformation bands, which may form at various stages during the folding process. Defining the distribution, orientation, and the type of fold-related structures and understanding the relationships between folding and fracturing is significant both for theoretical and practical purposes. Furthermore, as the deformation related to the folding process influences fluid flow through rocks, identifying the types of structures formed during folding is as important as predicting their geometries. To unravel the relationship between mechanical stratigraphy and folding process, the well-exposed Cingoli anticline (Northern Apennines), has been studied in detail. The Upper Cretaceous-Middle Eocene stratigraphy of the Cingoli anticline is characterized by a pelagic multilayer made up of fine-grained pelagic limestones and, marly limestones, in places alternated with thin continuous chert layers. The presence of several outcrops located in different structural positions of the anticline makes the Cingoli anticline an excellent natural laboratory to investigate relationships between folding, fracturing, and mechanical stratigraphy relative to the structural setting of the fold. The field data collected show that high angle to bedding PSSs, which formed before tilting and during the first stage of folding, are not homogeneously distributed in the pelagic limestones. Generally, high angle to bedding PSSs form in the marly pelagic limestones and they have been observed in several outcrops and in different structural positions except where the marly limestones are inter-bedded with stiffer chert layers. In order to analyse theoretically what observed in the field, we compared the deformation of limestones and chert layers with the deformation acting on fiber composites. In the mechanics of materials, composites refer to a matrix reinforced with particles, fibers, or laminae. During the early stage of folding, when the compressive stress is almost bedding parallel, chert layers act as a stiff lamina embedded in a weak limestone matrix. As a result, the stress is partitioned and the chert layers bear the greatest stress. Considering the mechanical properties (Poisson and Young's modulus) of the two materials (chert and limestone), and the estimated tectonic stress acting at the onset of the folding process, the stress magnitude in the limestone beds does not reach the expected value for the onset of pressure solution. For this reason, pelagic limestones containing chert layers are mainly characterized by joints whereas PSSs form in pelagic limestones without the stiffer phase (chert). This study suggests that within the same fold, and even within the same formation, different mechanical units can be characterized by different fractures types and fluid flow behaviour as a result of mechanical stratigraphy distribution.
Journal of Structural Geology, 2016
Journal of the Geological Society, 2003
Bulletin De La Societe Geologique De France, 2011
Geophysical Research Letters, 2008
Journal of Structural Geology, 2003
We studied the nucleation and growth of cataclastic fault cores from fractured damage zones in ex... more We studied the nucleation and growth of cataclastic fault cores from fractured damage zones in extensional and strike-slip fault zones in carbonate rocks. Analysed fault zones have similar protolith lithology and sedimentary fabric, but different geometry, kinematics, size, tectonic environment and deformation history. Orthorhombic rock lithons, a few decimetres in size, characterise the structural fabric of damage zones. Lithons derive from the intersection of a dominant fracture/cleavage set with bedding and/or joints. At the damage zone-fault core transition, orthorhombic lithons reduce in size and approach an isometric shape. Their cross-sectional aspect ratio has an average value of 1.4. Analysed fault cores have similar rock textures, sorting and comminution degree. Particle-size distributions of fault core rocks show linear trends in log-log graphs and average fractal dimension of 2.5. Our results on rock fabrics suggest that fault core development initiates from rock masses in damage zones, where the shape anisotropy of orthorhombic lithons favours additional fracturing at high angle to their long axes. Eventually, smaller, nearly isometric lithons generate from repeated fracturing of orthorhombic lithons. When the aspect ratio of these lithons approaches the threshold value of about 1.4, particle rotation is favoured and cataclastic flow starts. Owing to the granular nature of the damage zone-fault core transitions in carbonate rocks, analogies with the nucleation of deformation bands in sandstones can be established. Our results may be of use to the industry for quantitative characterisation of fault zone permeability. According to the proposed model, radical changes on the permeability properties are expected during the growth of fault cores.
ABSTRACT Thrust fault-related folds in carbonate rocks are characterized by deformation accommoda... more ABSTRACT Thrust fault-related folds in carbonate rocks are characterized by deformation accommodated by different kinds of structures, such as joints, faults, pressure solution seams (PSSs), and deformation bands, which may form at various stages during the folding process. Defining the distribution, orientation, and the type of fold-related structures and understanding the relationships between folding and fracturing is significant both for theoretical and practical purposes. Furthermore, as the deformation related to the folding process influences fluid flow through rocks, identifying the types of structures formed during folding is as important as predicting their geometries. To unravel the relationship between mechanical stratigraphy and folding process, the well-exposed Cingoli anticline (Northern Apennines), has been studied in detail. The Upper Cretaceous-Middle Eocene stratigraphy of the Cingoli anticline is characterized by a pelagic multilayer made up of fine-grained pelagic limestones and, marly limestones, in places alternated with thin continuous chert layers. The presence of several outcrops located in different structural positions of the anticline makes the Cingoli anticline an excellent natural laboratory to investigate relationships between folding, fracturing, and mechanical stratigraphy relative to the structural setting of the fold. The field data collected show that high angle to bedding PSSs, which formed before tilting and during the first stage of folding, are not homogeneously distributed in the pelagic limestones. Generally, high angle to bedding PSSs form in the marly pelagic limestones and they have been observed in several outcrops and in different structural positions except where the marly limestones are inter-bedded with stiffer chert layers. In order to analyse theoretically what observed in the field, we compared the deformation of limestones and chert layers with the deformation acting on fiber composites. In the mechanics of materials, composites refer to a matrix reinforced with particles, fibers, or laminae. During the early stage of folding, when the compressive stress is almost bedding parallel, chert layers act as a stiff lamina embedded in a weak limestone matrix. As a result, the stress is partitioned and the chert layers bear the greatest stress. Considering the mechanical properties (Poisson and Young's modulus) of the two materials (chert and limestone), and the estimated tectonic stress acting at the onset of the folding process, the stress magnitude in the limestone beds does not reach the expected value for the onset of pressure solution. For this reason, pelagic limestones containing chert layers are mainly characterized by joints whereas PSSs form in pelagic limestones without the stiffer phase (chert). This study suggests that within the same fold, and even within the same formation, different mechanical units can be characterized by different fractures types and fluid flow behaviour as a result of mechanical stratigraphy distribution.
Tectonophysics, 2016
A giant carbonate vein (≥50 m thick; fissure ridge travertines) and nearby travertine plateaus in... more A giant carbonate vein (≥50 m thick; fissure ridge travertines) and nearby travertine plateaus in the Semproniano area (Mt. Amiata geothermal field, southern Tuscany, Italy) are investigated through a multidisciplinary approach, including field and laboratory geochemical analyses (U/Th geochronology, C, Nd, O and Sr isotope systematics, REE abundances, and fluid inclusion microthermometry). The main aim of this work is to understand: (1) modes and rates for the growth of the giant vein and nearby travertine deposits within a Quaternary volcano-tectonic domain; (2) implications in terms of the CO 2 leakage; and (3) possible relationships with Quaternary paleoclimate and hydrological oscillations. Results show that the giant vein was the inner portion of a large fissure ridge travertine and grew asymmetrically and ataxially through repeated shallow fluid injections between N650 and 85 ka, with growth rates in the 10 −2 –10 −3 mm/a order. The giant vein developed mainly during warm humid (interglacial) periods, partially overlapping with the growth of nearby travertine plateaus. Estimated values of CO 2 leakage connected with the vein precipitation are between about 5 × 10 6 and 3 × 10 7 mol a −1 km − 2 , approximately representing one millionth of the present global CO 2 leakage from volcanic areas. Temperature estimates obtained from O-isotopes and fluid inclusion microthermometry indicate epithermal conditions (90–50 °C) for the circulating fluid during the giant vein growth, with only slight evidence of cooling with time. Geochemical and isotope data document that the travertine deposits formed mainly during Pleistocene warm humid periods, within a tectonically-controlled convective fluid circuit fed by meteoric infiltration and maintained by the regional geothermal anomaly hosted by the carbonate reservoir of the Mt. Amiata field.
Asbestos-bearing rock sequences constitute a remarkable natural hazard that poses important threa... more Asbestos-bearing rock sequences constitute a remarkable natural hazard that poses important threat to human health and may be at the origin of diseases such as asbestosis, mesothelioma and lung cancer). Presently, asbestos is classified as Category 1 carcinogen by world health authorities. Although regulatory agencies in many countries prohibit or restrict the use of asbestos, and discipline the environmental asbestos exposure, the impact of asbestos on human life still constitutes a major problem. Naturally occurring asbestos includes serpentine and amphibole minerals characterised by fibrous morphology and it is a constituent of mineralogical associations typical of mafic and ultramafic rocks within the ophiolitic sequences. Release of fibres can occur both through natural processes (erosion) and through human activities requiring fragmentation of ophiolite rocks (quarrying, tunnelling, railways construction, etc.). As a consequence, vulnerability is increasing in sites where workers and living people are involved by dispersion of fibres during mining and milling of ophiolitic rocks. By analysing in the field different exposures of ophiolitic sequences from the Italian peninsula and after an extensive review of the existing literature, we remark the importance of the geological context (origin, tectonic and deformation history) of ophiolites as a first-order parameter in evaluating the asbestos hazard. Integrated structural, textural, mineralogical and petrological studies significantly improve our understanding of the mechanisms governing the nucleation/growth of fibrous minerals in deformation structures (both ductile and brittle) within the ophiolitic rocks. A primary role is recognised in the structural processes favouring the fibrous mineralization, with correlation existing between the fibrous parameters (such as mineralogical composition, texture, mechanics characteristics) and the particles released in the air (such as shape, size, and amount liberated during rock fragmentation). Accordingly, we are confident that definition of an analytical protocol based on the geological attributes of the asbestos-bearing rocks may constitute a propaedeutical tool to evaluate the asbestos hazard in natural environments. This approach may have important implications for mitigation effects of the asbestos hazard from the medical field to the engineering operations.
We describe the evolution of the deformation pattern at Etna in the July-August 2001 eruption. Se... more We describe the evolution of the deformation pattern at Etna in the July-August 2001 eruption. Seismicity started the 13th of July and ground deformations culminated the 16th, developing of a N-S graben ~500 m wide and ~1 m deep at Montagnola (~3 km south of the summit craters). Contemporaneously, the 16th, the eruption started from the summit crater, where it
Geomorphology, 2016
Sinkholes and other karst structures in settled carbonate lands can be a significant source of ha... more Sinkholes and other karst structures in settled carbonate lands can be a significant source of hazard for humans and human works. Acque Albule, the study area of this work, is a Plio-Pleistocene basin near Rome, central Italy, superficially filled by a large and thick deposit of late Pleistocene thermogene travertine. Human activities blanket large portions of the flat territory covering most evidence from geological surface processes and potentially inducing scientists and public officials to underestimate some natural hazards including those connected with sinkholes. To contribute to the proper assessment of these hazards, a geomorphologic study of the basin was performed using digital elevation models (DEMs), recent aerial photographs, and field surveys. Historical material such as old aerial photographs and past geomorphologic studies both pre-dating the most part of quarrying and village building was also used together with memories of the elderly population. This preliminary study pointed out the presence of numerous potentially active sinkholes that are at present largely masked by either quarrying or overbuilding. Where this first study pointed out the apparent absence of sinkholes in areas characterized by high density of buildings, a detailed subsurface study was performed using properly-calibrated electrical resistivity tomography (ERT) and dynamic penetration measurements (DPSH), together with some borehole logs made available from the local municipality. This second study highlighted the presence of sinkholes and caves that are, this time, substantially hidden to the resolution of standard methods and materials such as aerial photographs, DEMs, and field surveys. Active sinkhole subsidence in the Acque Albule Basin may explain, at least in part, the frequent damages that affect numerous buildings in the area. The main conclusion from this study is that the mitigation of sinkhole hazard in highly populated areas has to pass through a thorough search of (hidden) sinkholes that can be masked by the Anthropocenic molding and blanketing of the territory. For these purposes, data from historical (pre-Anthropocene) documents as well as, where possible, subsurface investigations are fundamental.
Bollettino Societa Geologica Italiana, 2000
... il criterio dei rolax trattato in Salvini & Vittori (1982) ed è slato realizzalo auto... more ... il criterio dei rolax trattato in Salvini & Vittori (1982) ed è slato realizzalo automaticamente con l'ausilio del software DAISY 2.6 (Salvini ... dissoluzione (Pantano S. Egidio, Faglia di Mattinata), b) Faglia inversa con superfici di clivaggio al letto (S. Marco in Lamis, ramo transpressivo ...
The evolution of fracturing and cataclasis influences the mechanical and permeability properties ... more The evolution of fracturing and cataclasis influences the mechanical and permeability properties of fault zones. Fault zones can behave as strong or weak mechanical discontinuities and as conduits or barriers to fluid flow mainly depending on the nature and amount of cataclastic rocks that developed in their cores. Our structural investigations in fault zones affecting carbonate platform rocks in the Apennines, Italy, allow us to propose an evolutionary model for the progressive development of cataclastic fault core rocks from damage zones, and for the progression of cataclasis in fault cores. Analyses of particle size in the cataclastic rocks show power law distributions with fractal dimensions spanning over a broad range. This suggests that the idea of a persistent fragmentation mechanism (self-similar cataclasis) for describing the entire evolution of natural cataclastic fault cores in carbonate rocks is inadequate. Self-similar evolution for the cataclastic process is a concept mainly derived from laboratory experiments and micromechanical modelling. Conversely, we propose that the fragmentation mechanism progressively changes with the intensity of comminution. Slip localisation within narrow shear bands is favoured when a favourable cataclastic fabric with fractal dimensions D ˜ 2.6-2.7 is achieved in the fault zone. Intense comminution in the narrow shear zones produces the preferential formation of small diameter particles resulting in particle size distributions characterised by D-values approaching or exceeding 3. The progression pathway of fracturing in damage zones and the non self-similar evolution of cataclasis in fault rocks have an important impact on the frictional and permeability properties of fault zones.
The Central Apennine are one of the most seismically active regions in the Mediterranean area and... more The Central Apennine are one of the most seismically active regions in the Mediterranean area and is affected by moderate to large shallow earthquakes that enucleate in and propagate through carbonate rocks. In this work we present a detailed fieldwork and microstructural analysis to define the architecture and deformation mechanisms of an exhumed fault zone in carbonates, the Tre Monti fault, at the northern boundary of the Fucino Basin. Fault rocks assemblages show differences in deformation mechanisms between the main and external fault planes, and subsidiary fault planes developed within the damage zone. We infer that this variety of fault rocks represents different deformation processes acting during different stages of fault development and fluid circulation. The multidisciplinary but field-based study of fault surfaces and fault rocks is fundamental to reveal the geological record of past earthquakes and seismic cycles and is strongly complementary to the seismological-based ...
ABSTRACT Thrust fault-related folds in carbonate rocks are characterized by deformation accommoda... more ABSTRACT Thrust fault-related folds in carbonate rocks are characterized by deformation accommodated by different kinds of structures, such as joints, faults, pressure solution seams (PSSs), and deformation bands, which may form at various stages during the folding process. Defining the distribution, orientation, and the type of fold-related structures and understanding the relationships between folding and fracturing is significant both for theoretical and practical purposes. Furthermore, as the deformation related to the folding process influences fluid flow through rocks, identifying the types of structures formed during folding is as important as predicting their geometries. To unravel the relationship between mechanical stratigraphy and folding process, the well-exposed Cingoli anticline (Northern Apennines), has been studied in detail. The Upper Cretaceous-Middle Eocene stratigraphy of the Cingoli anticline is characterized by a pelagic multilayer made up of fine-grained pelagic limestones and, marly limestones, in places alternated with thin continuous chert layers. The presence of several outcrops located in different structural positions of the anticline makes the Cingoli anticline an excellent natural laboratory to investigate relationships between folding, fracturing, and mechanical stratigraphy relative to the structural setting of the fold. The field data collected show that high angle to bedding PSSs, which formed before tilting and during the first stage of folding, are not homogeneously distributed in the pelagic limestones. Generally, high angle to bedding PSSs form in the marly pelagic limestones and they have been observed in several outcrops and in different structural positions except where the marly limestones are inter-bedded with stiffer chert layers. In order to analyse theoretically what observed in the field, we compared the deformation of limestones and chert layers with the deformation acting on fiber composites. In the mechanics of materials, composites refer to a matrix reinforced with particles, fibers, or laminae. During the early stage of folding, when the compressive stress is almost bedding parallel, chert layers act as a stiff lamina embedded in a weak limestone matrix. As a result, the stress is partitioned and the chert layers bear the greatest stress. Considering the mechanical properties (Poisson and Young's modulus) of the two materials (chert and limestone), and the estimated tectonic stress acting at the onset of the folding process, the stress magnitude in the limestone beds does not reach the expected value for the onset of pressure solution. For this reason, pelagic limestones containing chert layers are mainly characterized by joints whereas PSSs form in pelagic limestones without the stiffer phase (chert). This study suggests that within the same fold, and even within the same formation, different mechanical units can be characterized by different fractures types and fluid flow behaviour as a result of mechanical stratigraphy distribution.