Mt. Etna (Sicily, Italy) is one of the most active on Earth. Instability of the eastern and south... more Mt. Etna (Sicily, Italy) is one of the most active on Earth. Instability of the eastern and southern flanks, in terms of slow spreading and seismic activity of the volcano, is a dominant dynamic processes and is considered as a triggering mechanism of the eruptive activity. Extrusive lava flows were the subject of a number of laboratory studies aimed to investigate the evolution of physical parameters under cyclic loading. However, no temperature effects were investigated and more importantly only the shallow layers (~ 1.5km of depth) is made up of volcanites; the volcanic pile rests upon thick Mesozoic to Middle Pleistocene sedimentary sequences imbricated at the front of the Apennian-Maghrebian thrust belt. A variety of lithologies spanning from poorly consolidated terrigenous sediments to overconsolidated clays makes this sedimentary sequence and enhances the slow spreading detected. The tickest sequences are given from Triassic to Cretaceous carbonatic rocks (limestones and dolo...
We present a K-feldspar–liquid hygrometer specific to alkaline differentiated magmas that is cali... more We present a K-feldspar–liquid hygrometer specific to alkaline differentiated magmas that is calibrated through the regression analysis of sanidine and anorthoclase crystals coexisting with trachyte and phonolite melts. Partial-regression leverage plots were used to determine the minimum number of regression parameters that closely describe the variance of the dataset. The derived model was tested using K-feldspar–liquid pairs not included into the calibration dataset in order to address issues of systematic errors. When K-feldspar and plagioclase crystals coprecipitate from the same alkaline liquid under identical P-T-X-fO2-H2O conditions, the ability prediction of the new hygrometer is comparable to that of previous plagioclase–liquid models. To minimize the error of H2O estimate caused by the inadvertent use of disequilibrium data in natural samples, we have also calibrated a new test for equilibrium based on Or–Ab exchange between K-feldspar and coexisting melt. As an immediate ...
We present new thermometers and barometers based on clinopyroxene–liquid equilibria specific to a... more We present new thermometers and barometers based on clinopyroxene–liquid equilibria specific to alkaline differentiated magmas. The new models were calibrated through the regression analyses of experimental datasets obtained by merging phase equilibria experiments from the literature with new experiments performed by using trachytic and phonolitic starting compositions. The regression strategy was twofold: (1) we have tested previous thermometric and barometric equations and recalibrated these models using the new datasets; (2) we have calibrated a new thermometer and a new barometer including only regression parameters that closely describe the compositional variability of the datasets. The new models yield more precise estimates than previous thermometers and barometers when used to predict temperatures and pressures of alkaline differentiated magmas. We have tested the reliability of the new equations by using clinopyroxene–liquid pairs from trachytes and phonolites erupted durin...
The compositional variation of plagioclase and the partitioning of major elements between plagioc... more The compositional variation of plagioclase and the partitioning of major elements between plagioclase and melt have been experimentally measured as a function of the cooling rate. Crystals were grown from a basaltic melt at a pressure of 500 MPa under (i) variable cooling rates of 0.5, 2.1, 3, 9.4, and 15 °C/min from 1250 °C down to 1000 °C, (ii) quenching temperatures of 1025, 1050, 1075, 1090, and 1100 °C at the fixed cooling rate of 0.5 °C/min, and (iii) isothermal temperatures of 1000, 1025, 1050, 1075, 1090, and 1100 °C. Our results show that euhedral, faceted plagioclases form during isothermal and slower cooling experiments exhibiting idiomorphic tabular shapes. In contrast, dendritic shapes are observed from faster cooled charges. As the cooling rate is increased, concentrations of Al + Ca + Fe + Mg increase and Si + Na + K decrease in plagioclase favoring higher An and lower Ab + Or contents. Significant variations of pl–liqKd are also observed by the comparison between iso...
A number of measurements on physical properties of volcanic tuff from different volcanic Italian ... more A number of measurements on physical properties of volcanic tuff from different volcanic Italian districts (Campi Flegrei, Colli Albani, Lago di Vico) has been performed in the recent years. Petrophysical investigations carried out at increasing/decreasing effective pressure (Vinciguerra et al., 2005; 2008) revealed how, within the same lithology, the different degree of lithification and presence of clasts can affect significantly physical property values. Microstructural analyses revealed that the pressurization and depressurization cycles generate inelastic crack damage/pore collapse and permanent reduction of voids space. When cores from boreholes were investigated, significant variations of physical properties have been found even within the same tuff lithologies (Vinciguerra et al., 2008), which significantly influence the modelling of the overall physics and mechanics, as well as the input parameters for ground deformation and seismicity modelling. In this study we analysed t...
The compositional variation of clinopyroxene and the partitioning of major elements between clino... more The compositional variation of clinopyroxene and the partitioning of major elements between clinopyroxene and melt are estimated as a function of the cooling rate. Clinopyroxenes were crystallized under variable cooling regimes (15, 9.4, 3, 2.1, and 0.5°C/min from 1250 down to 1000°C) and at isothermal conditions of 1000°C from a basaltic composition at a pressure of 500MPa under anhydrous and hydrous (H2O=1.3wt.%) conditions. The clinopyroxene chemistry shows that, as the cooling rate increases, crystals are progressively depleted in Ca, Mg, Fe2+ and Si and enriched in Na, Fe3+, Al (mainly AlIV), and Ti. Di and Hd versus CaTs and CaFeTs form a continuous binary solid solution characterized by higher amounts of tschermakitic components with increasing cooling rate. Two parameters (DH=Di+Hd and TE=CaTs+CaFeTs+En) are calculated to describe the effect of cooling rate on the clinopyroxene composition. The variation of DH/TE with increasing cooling rate evidences the kinetic process ind...
Two sets of cooling experiments were run at 500 MPa conditions for one anhydrous and one hydrous ... more Two sets of cooling experiments were run at 500 MPa conditions for one anhydrous and one hydrous (H2O = 1.3 wt.%) starting basaltic melts: a) five cooling rates (15, 9.4, 3, 2.1, and 0.5 °C/min) between 1250 and 1000 °C, and b) a 0.5 °C/min cooling rate from 1250 to 1191, 1167, 1100, 1090, 1075, 1050, 1025 and 1000 °C final temperatures. Cooling rate plays a major role in the differentiation of run products. At the lower cooling rate, glasses of tephri-phonolitic and trachy-andesitic composition have been detected. At comparable cooling rate, the dry glasses show a larger compositional variability and degree of differentiation than the hydrous products. The amount of crystallizing solid phases is always larger in the dry products. It is strongly controlled by both cooling rate and water content and massive crystallization occurs only at lower cooling rates. At a constant cooling rate, massive crystallization is observed at lower temperatures. Clinopyroxene, plagioclase and oxide occ...
Calcite crystals are relatively common in alkalic hypoabyssalite and kimberlite rocks, but rarely... more Calcite crystals are relatively common in alkalic hypoabyssalite and kimberlite rocks, but rarely documented in effusive rocks (e.g. alkaline lava flows). Magmatic calcite in effusive rocks has been usually related to mantle-origine carbonate; only in very few cases, it has been explained throughout magma-sediments interaction. The ultrapotassic Colli Albani Volcanic District (Central Italy) represents one of the most peculiar volcanic districts on the Earth because of its liquid line of descent characterized by differentiated, low silica (SiO2≤45wt%), K-foiditic magmas. Field, geochemical, and experimental studies have demonstrated that such a differentiation trend, starting from trachybasaltic parental magma, is mainly due to magma-carbonate sediments interaction. One of the most intriguing question concerning Colli Albani petrology is the occurrence of calcite crystals in the groundmass of some lava flows. In general, Colli Albani lava flows are made up of leucite and clinopyroxe...
Vulcano Island (Aelioan Archipelago, Italy) is a composite structure consisting of four eruptive ... more Vulcano Island (Aelioan Archipelago, Italy) is a composite structure consisting of four eruptive systems (Vulcano Primordiale, Complesso della Lentia, Cono di La Fossa and Vulcanello) and two polyphasic calderas, Caldera del Piano and Caldera di La Fossa. On the north-eastern side of Vulcano Island, a minor eruptive center, Monte Luccia, is located. The sequence consists of a shoshonitec lava at
A number of measurements on physical properties of volcanic tuff from different volcanic Italian ... more A number of measurements on physical properties of volcanic tuff from different volcanic Italian districts (Campi Flegrei, Colli Albani, Lago di Vico) has been performed in the recent years. Petrophysical investigations carried out at increasing/decreasing effective pressure (Vinciguerra et al., 2005; 2008) revealed how, within the same lithology, the different degree of lithification and presence of clasts can affect significantly
ABSTRACT The importance and economic interest on rocksalt deposits and salt bodies are well known... more ABSTRACT The importance and economic interest on rocksalt deposits and salt bodies are well known and extensively studied. The physical and mechanical properties of salt have a profound influence on the tectonics as well as they are considered to be vital for applicative purposes such as mining, petroleum and nuclear waste storage. However, previous scientific works have mainly focused on synthetic rocksalt or commercial salt, whereas natural salt facies have been scarcely investigated. In this view, we present new data on the role of natural heterogeneities (i.e., relative abundance of primary salt crystals and impurities) on the rheological parameters of a rocksalt. This rock belongs to the Saline di Volterra formation (Volterra basin, Tuscany, central Italy) that was deposited during the Messinian Salinity Crisis. The 49-metre-thick salt sequence (intersected by the S1113 borehole of the Solvay company) is characterized by a high salt facies variability. In particular, three end-members have been recognized: the first contains abundant primary salt crystals, with minor or no recrystallizazion; the second member is extensively recrystallized, with scarce primary crystal remnants; the third shows a great abundance of clay impurities. Rheological parameters, such as static and dynamic Young's Modulus and coefficient of linear expansion, were measured for the three rocksalt end-members throughout P and S seismic velocities, uniaxial compressive strength and thermal expansion measurements. Seismic velocity has been measured on cubic samples with a side ranging from 4 to 7 cm. A clear effect of the salt facies was found: the average velocity is faster in mostly recrystallized salt samples (4500 m/s), slower in primary salt-rich samples (4300 m/s), and intermediate (4350 m/s) in presence of clay impurities. Dynamic Young's Modulus calculated on velocities (average value ≈ 38 GPa) mirrors this behavior, with lowest values related to primary salt. The anisotropic effect induced by the deformation is evident considering the wave velocities measured for each axis of the cubes, with lower velocities along the Z (vertical) axis. Uniaxial compressive tests (carried out at ambient temperature) revealed the effect of the salt facies in the mechanical properties and, particularly, in the elastic properties and in the absolute peak stress value. Static Young's Moduli (average value ≈ 5,3 GPa) result much lower than the dynamic ones. In this case lowest values are related to recrystallized salt. Notably, the peak stress is inversely proportional to the static Young's Moduli. Moreover, data from thermal expansion curves (from 20 to 700 °C) show a greater amount of volume expansion of primary salt and allowed to identify an “instability zone”, between 300 and 500 °C, where fluid emission, samples cracking and a sudden increase in volume expansivity occur. Results from our experiments indicate that the different characteristics of salt facies determine the bulk rheological parameters and, consequently, the rocksalt deformation behavior. Although further analyses are necessary, we suggest that studies on salt bodies cannot be approached without detailed petrophysical and rheological analyses of rocksalt facies.
It is well established that discontinuities, including porosity, within rock masses and laborator... more It is well established that discontinuities, including porosity, within rock masses and laboratory specimens influence the engineering properties of rock. Discontinuities are often assumed to be evenly distributed throughout a rock mass or laboratory specimen. Numerous ...
ABSTRACT We present results from magma-carbonate interaction experiments designed to shed light o... more ABSTRACT We present results from magma-carbonate interaction experiments designed to shed light on the geochemical evolution of clinopyroxene in the Roman Province (central Italy). Atmospheric pressure experiments were performed at 1140, 1160 and 1180 °C under NNO, MH and air oxygen buffering conditions. The starting materials were a shoshonite and a phonotephrite doped with different amounts of CaO and CaO + MgO whose stoichiometric proportions reproduced the assimilation by magmas of calcite and dolomite, respectively. The results show that clinopyroxenes, spinels and residual glasses are ubiquitous phases in all run-products. Calcite-doped runs crystallize more clinopyroxene than dolomite-doped runs at the same conditions. This leads to the formation of strong desilicated CaO-rich melts showing compositions comparable to those of magmatic skarns. During magma-carbonate interaction, the content of Fe3 + in clinopyroxene increases with increasing fO2 promoting the substitution of Al for Si in tetrahedral site. Local charge imbalances are also compensated by the incorporation of highly charged cations, such as Ti, into the crystal lattice. According to this cation substitution, Al-Ca-Fe3 +-Ti-rich clinopyroxenes of the skarn environment testify to continuous CO2 fluxes produced by the thermal decomposition of carbonate wall-rocks. Nevertheless, the oxidative capacity of CO2 progressively decreases from the skarn shells towards the interior of the magma chamber driving the crystallization of Si-Fe2 +-Mg-rich clinopyroxenes.
ABSTRACT Carbonate-bearing normal faults are important structures for controlling fluid flow and ... more ABSTRACT Carbonate-bearing normal faults are important structures for controlling fluid flow and seismogenesis within the brittle upper crust. Numerous studies have tried to characterize fault zone structure and earthquake slip processes along carbonate-bearing faults. However, due to the different scales of investigation, these studies are not often integrated to provide a comprehensive fault image. Here we present a multi-scale investigation of a normal fault exhumed from seismogenic depths. The fault extends for a length of 10 km with a maximum width of about 1.5 km and consists of 5 sub-parallel and interacting segments. The maximum displacement (370-650 m) of each fault segment is partitioned along sub-parallel slipping zones extending for a total width of about 50 m. Each slipping zone is characterized by slipping surfaces exhibiting different slip plane phenomena. Fault rock development is controlled by the protolith lithology. In massive limestone, moving away from the slip surface, we observe a thin layer (<2 cm) of ultracataclasite, cataclasite (2-10 cm) and fault breccia. In marly limestone, the fault rock consists of a cataclasite with hydrofractures and smectite-rich pressure solution seams. At the micro-nano scale, the slip surface consists of a continuous and thin (<300 μm) layer composed of coarse calcite grains (∼5–20 μm in size) associated with sub-micrometer grains showing fading grain boundaries, voids and/or vesicles, and suggesting thermal decomposition processes. Micrometer-sized calcite crystals show nanoscale polysynthetic twinning affected by the occurrence of subgrain boundaries and polygonalized nanostructures. Investigations at the kilometres-tens of meter scale provide fault images that can be directly compared with high-resolution seismological data and when combined can be used to develop a comprehensive characterization of seismically active fault structures in carbonate lithologies. Micro and nanoscale investigations along the principal slipping zone suggest that different deformation processes, including plastic deformation and thermal decomposition, were active during seismic slip.
Mt. Etna (Sicily, Italy) is one of the most active on Earth. Instability of the eastern and south... more Mt. Etna (Sicily, Italy) is one of the most active on Earth. Instability of the eastern and southern flanks, in terms of slow spreading and seismic activity of the volcano, is a dominant dynamic processes and is considered as a triggering mechanism of the eruptive activity. Extrusive lava flows were the subject of a number of laboratory studies aimed to investigate the evolution of physical parameters under cyclic loading. However, no temperature effects were investigated and more importantly only the shallow layers (~ 1.5km of depth) is made up of volcanites; the volcanic pile rests upon thick Mesozoic to Middle Pleistocene sedimentary sequences imbricated at the front of the Apennian-Maghrebian thrust belt. A variety of lithologies spanning from poorly consolidated terrigenous sediments to overconsolidated clays makes this sedimentary sequence and enhances the slow spreading detected. The tickest sequences are given from Triassic to Cretaceous carbonatic rocks (limestones and dolo...
We present a K-feldspar–liquid hygrometer specific to alkaline differentiated magmas that is cali... more We present a K-feldspar–liquid hygrometer specific to alkaline differentiated magmas that is calibrated through the regression analysis of sanidine and anorthoclase crystals coexisting with trachyte and phonolite melts. Partial-regression leverage plots were used to determine the minimum number of regression parameters that closely describe the variance of the dataset. The derived model was tested using K-feldspar–liquid pairs not included into the calibration dataset in order to address issues of systematic errors. When K-feldspar and plagioclase crystals coprecipitate from the same alkaline liquid under identical P-T-X-fO2-H2O conditions, the ability prediction of the new hygrometer is comparable to that of previous plagioclase–liquid models. To minimize the error of H2O estimate caused by the inadvertent use of disequilibrium data in natural samples, we have also calibrated a new test for equilibrium based on Or–Ab exchange between K-feldspar and coexisting melt. As an immediate ...
We present new thermometers and barometers based on clinopyroxene–liquid equilibria specific to a... more We present new thermometers and barometers based on clinopyroxene–liquid equilibria specific to alkaline differentiated magmas. The new models were calibrated through the regression analyses of experimental datasets obtained by merging phase equilibria experiments from the literature with new experiments performed by using trachytic and phonolitic starting compositions. The regression strategy was twofold: (1) we have tested previous thermometric and barometric equations and recalibrated these models using the new datasets; (2) we have calibrated a new thermometer and a new barometer including only regression parameters that closely describe the compositional variability of the datasets. The new models yield more precise estimates than previous thermometers and barometers when used to predict temperatures and pressures of alkaline differentiated magmas. We have tested the reliability of the new equations by using clinopyroxene–liquid pairs from trachytes and phonolites erupted durin...
The compositional variation of plagioclase and the partitioning of major elements between plagioc... more The compositional variation of plagioclase and the partitioning of major elements between plagioclase and melt have been experimentally measured as a function of the cooling rate. Crystals were grown from a basaltic melt at a pressure of 500 MPa under (i) variable cooling rates of 0.5, 2.1, 3, 9.4, and 15 °C/min from 1250 °C down to 1000 °C, (ii) quenching temperatures of 1025, 1050, 1075, 1090, and 1100 °C at the fixed cooling rate of 0.5 °C/min, and (iii) isothermal temperatures of 1000, 1025, 1050, 1075, 1090, and 1100 °C. Our results show that euhedral, faceted plagioclases form during isothermal and slower cooling experiments exhibiting idiomorphic tabular shapes. In contrast, dendritic shapes are observed from faster cooled charges. As the cooling rate is increased, concentrations of Al + Ca + Fe + Mg increase and Si + Na + K decrease in plagioclase favoring higher An and lower Ab + Or contents. Significant variations of pl–liqKd are also observed by the comparison between iso...
A number of measurements on physical properties of volcanic tuff from different volcanic Italian ... more A number of measurements on physical properties of volcanic tuff from different volcanic Italian districts (Campi Flegrei, Colli Albani, Lago di Vico) has been performed in the recent years. Petrophysical investigations carried out at increasing/decreasing effective pressure (Vinciguerra et al., 2005; 2008) revealed how, within the same lithology, the different degree of lithification and presence of clasts can affect significantly physical property values. Microstructural analyses revealed that the pressurization and depressurization cycles generate inelastic crack damage/pore collapse and permanent reduction of voids space. When cores from boreholes were investigated, significant variations of physical properties have been found even within the same tuff lithologies (Vinciguerra et al., 2008), which significantly influence the modelling of the overall physics and mechanics, as well as the input parameters for ground deformation and seismicity modelling. In this study we analysed t...
The compositional variation of clinopyroxene and the partitioning of major elements between clino... more The compositional variation of clinopyroxene and the partitioning of major elements between clinopyroxene and melt are estimated as a function of the cooling rate. Clinopyroxenes were crystallized under variable cooling regimes (15, 9.4, 3, 2.1, and 0.5°C/min from 1250 down to 1000°C) and at isothermal conditions of 1000°C from a basaltic composition at a pressure of 500MPa under anhydrous and hydrous (H2O=1.3wt.%) conditions. The clinopyroxene chemistry shows that, as the cooling rate increases, crystals are progressively depleted in Ca, Mg, Fe2+ and Si and enriched in Na, Fe3+, Al (mainly AlIV), and Ti. Di and Hd versus CaTs and CaFeTs form a continuous binary solid solution characterized by higher amounts of tschermakitic components with increasing cooling rate. Two parameters (DH=Di+Hd and TE=CaTs+CaFeTs+En) are calculated to describe the effect of cooling rate on the clinopyroxene composition. The variation of DH/TE with increasing cooling rate evidences the kinetic process ind...
Two sets of cooling experiments were run at 500 MPa conditions for one anhydrous and one hydrous ... more Two sets of cooling experiments were run at 500 MPa conditions for one anhydrous and one hydrous (H2O = 1.3 wt.%) starting basaltic melts: a) five cooling rates (15, 9.4, 3, 2.1, and 0.5 °C/min) between 1250 and 1000 °C, and b) a 0.5 °C/min cooling rate from 1250 to 1191, 1167, 1100, 1090, 1075, 1050, 1025 and 1000 °C final temperatures. Cooling rate plays a major role in the differentiation of run products. At the lower cooling rate, glasses of tephri-phonolitic and trachy-andesitic composition have been detected. At comparable cooling rate, the dry glasses show a larger compositional variability and degree of differentiation than the hydrous products. The amount of crystallizing solid phases is always larger in the dry products. It is strongly controlled by both cooling rate and water content and massive crystallization occurs only at lower cooling rates. At a constant cooling rate, massive crystallization is observed at lower temperatures. Clinopyroxene, plagioclase and oxide occ...
Calcite crystals are relatively common in alkalic hypoabyssalite and kimberlite rocks, but rarely... more Calcite crystals are relatively common in alkalic hypoabyssalite and kimberlite rocks, but rarely documented in effusive rocks (e.g. alkaline lava flows). Magmatic calcite in effusive rocks has been usually related to mantle-origine carbonate; only in very few cases, it has been explained throughout magma-sediments interaction. The ultrapotassic Colli Albani Volcanic District (Central Italy) represents one of the most peculiar volcanic districts on the Earth because of its liquid line of descent characterized by differentiated, low silica (SiO2≤45wt%), K-foiditic magmas. Field, geochemical, and experimental studies have demonstrated that such a differentiation trend, starting from trachybasaltic parental magma, is mainly due to magma-carbonate sediments interaction. One of the most intriguing question concerning Colli Albani petrology is the occurrence of calcite crystals in the groundmass of some lava flows. In general, Colli Albani lava flows are made up of leucite and clinopyroxe...
Vulcano Island (Aelioan Archipelago, Italy) is a composite structure consisting of four eruptive ... more Vulcano Island (Aelioan Archipelago, Italy) is a composite structure consisting of four eruptive systems (Vulcano Primordiale, Complesso della Lentia, Cono di La Fossa and Vulcanello) and two polyphasic calderas, Caldera del Piano and Caldera di La Fossa. On the north-eastern side of Vulcano Island, a minor eruptive center, Monte Luccia, is located. The sequence consists of a shoshonitec lava at
A number of measurements on physical properties of volcanic tuff from different volcanic Italian ... more A number of measurements on physical properties of volcanic tuff from different volcanic Italian districts (Campi Flegrei, Colli Albani, Lago di Vico) has been performed in the recent years. Petrophysical investigations carried out at increasing/decreasing effective pressure (Vinciguerra et al., 2005; 2008) revealed how, within the same lithology, the different degree of lithification and presence of clasts can affect significantly
ABSTRACT The importance and economic interest on rocksalt deposits and salt bodies are well known... more ABSTRACT The importance and economic interest on rocksalt deposits and salt bodies are well known and extensively studied. The physical and mechanical properties of salt have a profound influence on the tectonics as well as they are considered to be vital for applicative purposes such as mining, petroleum and nuclear waste storage. However, previous scientific works have mainly focused on synthetic rocksalt or commercial salt, whereas natural salt facies have been scarcely investigated. In this view, we present new data on the role of natural heterogeneities (i.e., relative abundance of primary salt crystals and impurities) on the rheological parameters of a rocksalt. This rock belongs to the Saline di Volterra formation (Volterra basin, Tuscany, central Italy) that was deposited during the Messinian Salinity Crisis. The 49-metre-thick salt sequence (intersected by the S1113 borehole of the Solvay company) is characterized by a high salt facies variability. In particular, three end-members have been recognized: the first contains abundant primary salt crystals, with minor or no recrystallizazion; the second member is extensively recrystallized, with scarce primary crystal remnants; the third shows a great abundance of clay impurities. Rheological parameters, such as static and dynamic Young's Modulus and coefficient of linear expansion, were measured for the three rocksalt end-members throughout P and S seismic velocities, uniaxial compressive strength and thermal expansion measurements. Seismic velocity has been measured on cubic samples with a side ranging from 4 to 7 cm. A clear effect of the salt facies was found: the average velocity is faster in mostly recrystallized salt samples (4500 m/s), slower in primary salt-rich samples (4300 m/s), and intermediate (4350 m/s) in presence of clay impurities. Dynamic Young's Modulus calculated on velocities (average value ≈ 38 GPa) mirrors this behavior, with lowest values related to primary salt. The anisotropic effect induced by the deformation is evident considering the wave velocities measured for each axis of the cubes, with lower velocities along the Z (vertical) axis. Uniaxial compressive tests (carried out at ambient temperature) revealed the effect of the salt facies in the mechanical properties and, particularly, in the elastic properties and in the absolute peak stress value. Static Young's Moduli (average value ≈ 5,3 GPa) result much lower than the dynamic ones. In this case lowest values are related to recrystallized salt. Notably, the peak stress is inversely proportional to the static Young's Moduli. Moreover, data from thermal expansion curves (from 20 to 700 °C) show a greater amount of volume expansion of primary salt and allowed to identify an “instability zone”, between 300 and 500 °C, where fluid emission, samples cracking and a sudden increase in volume expansivity occur. Results from our experiments indicate that the different characteristics of salt facies determine the bulk rheological parameters and, consequently, the rocksalt deformation behavior. Although further analyses are necessary, we suggest that studies on salt bodies cannot be approached without detailed petrophysical and rheological analyses of rocksalt facies.
It is well established that discontinuities, including porosity, within rock masses and laborator... more It is well established that discontinuities, including porosity, within rock masses and laboratory specimens influence the engineering properties of rock. Discontinuities are often assumed to be evenly distributed throughout a rock mass or laboratory specimen. Numerous ...
ABSTRACT We present results from magma-carbonate interaction experiments designed to shed light o... more ABSTRACT We present results from magma-carbonate interaction experiments designed to shed light on the geochemical evolution of clinopyroxene in the Roman Province (central Italy). Atmospheric pressure experiments were performed at 1140, 1160 and 1180 °C under NNO, MH and air oxygen buffering conditions. The starting materials were a shoshonite and a phonotephrite doped with different amounts of CaO and CaO + MgO whose stoichiometric proportions reproduced the assimilation by magmas of calcite and dolomite, respectively. The results show that clinopyroxenes, spinels and residual glasses are ubiquitous phases in all run-products. Calcite-doped runs crystallize more clinopyroxene than dolomite-doped runs at the same conditions. This leads to the formation of strong desilicated CaO-rich melts showing compositions comparable to those of magmatic skarns. During magma-carbonate interaction, the content of Fe3 + in clinopyroxene increases with increasing fO2 promoting the substitution of Al for Si in tetrahedral site. Local charge imbalances are also compensated by the incorporation of highly charged cations, such as Ti, into the crystal lattice. According to this cation substitution, Al-Ca-Fe3 +-Ti-rich clinopyroxenes of the skarn environment testify to continuous CO2 fluxes produced by the thermal decomposition of carbonate wall-rocks. Nevertheless, the oxidative capacity of CO2 progressively decreases from the skarn shells towards the interior of the magma chamber driving the crystallization of Si-Fe2 +-Mg-rich clinopyroxenes.
ABSTRACT Carbonate-bearing normal faults are important structures for controlling fluid flow and ... more ABSTRACT Carbonate-bearing normal faults are important structures for controlling fluid flow and seismogenesis within the brittle upper crust. Numerous studies have tried to characterize fault zone structure and earthquake slip processes along carbonate-bearing faults. However, due to the different scales of investigation, these studies are not often integrated to provide a comprehensive fault image. Here we present a multi-scale investigation of a normal fault exhumed from seismogenic depths. The fault extends for a length of 10 km with a maximum width of about 1.5 km and consists of 5 sub-parallel and interacting segments. The maximum displacement (370-650 m) of each fault segment is partitioned along sub-parallel slipping zones extending for a total width of about 50 m. Each slipping zone is characterized by slipping surfaces exhibiting different slip plane phenomena. Fault rock development is controlled by the protolith lithology. In massive limestone, moving away from the slip surface, we observe a thin layer (<2 cm) of ultracataclasite, cataclasite (2-10 cm) and fault breccia. In marly limestone, the fault rock consists of a cataclasite with hydrofractures and smectite-rich pressure solution seams. At the micro-nano scale, the slip surface consists of a continuous and thin (<300 μm) layer composed of coarse calcite grains (∼5–20 μm in size) associated with sub-micrometer grains showing fading grain boundaries, voids and/or vesicles, and suggesting thermal decomposition processes. Micrometer-sized calcite crystals show nanoscale polysynthetic twinning affected by the occurrence of subgrain boundaries and polygonalized nanostructures. Investigations at the kilometres-tens of meter scale provide fault images that can be directly compared with high-resolution seismological data and when combined can be used to develop a comprehensive characterization of seismically active fault structures in carbonate lithologies. Micro and nanoscale investigations along the principal slipping zone suggest that different deformation processes, including plastic deformation and thermal decomposition, were active during seismic slip.
Uploads
Papers by Silvio Mollo