1,720,975 research outputs found
Transtensive faulting in carbonates at different crustal levels: Examples from SW Helvetics and Central Apennines
No full textTranstensive faulting in carbonates at different crustal levels: Examples from SW Helvetics and Central Apennines
No full textFault rocks at different crustal depths generate different fault structures and tectonites mostly depending on lithology, fluid flow and temperature. In this note we address the fault zone development and deformation mechanisms that occur in carbonate lithologies at different crustal levels. We compare faults exhumed near the brittleductile transition in the Helvetic Nappes in theAlps and similar faults from the upper crust in the Gran Sasso area in the Central Appenines. We observe the different role of deformation processes at different depth and lithology and assess the tendency for localization at the Brittle Ductile Transition
Fault-controlled volcanic vents between the Volsci Range and the magma-rich Tyrrhenian passive margin (Italy)
No full textTectonically controlled carbonate-seated maar-diatreme volcanoes. The case of the Volsci Volcanic Field, central Italy
No full textQuaternary carbonate-seated maar-diatremes in the Volsci Range are one of the most intriguing products of the west-directed subduction of the Adriatic slab that drove the development of the Apennine mountain belt in Central Italy. The Volsci Volcanic Field is characterized by phreatomagmatic surge deposits, rich in accidental carbonate lithics, and subordinate Strombolian scoria fall deposits and lava flows, locally sourced from some tens of monogenetic eruptive centers (at least fifty tuff rings and scoria cones). We investigate the subsurface maar-diatreme processes in terms of relationships between faulting and explosive magma-water interaction, as well as the distribution pattern of the eruptive centers. With this aim, we present the following new data: i) description of the fold-and-thrust belt structure and associated eruptive centers, ii) componentry of volcanic rock-types, iii) determination of grain-size, degrees of whiteness and roundness of carbonate lithic inclusions, iv) micropaleontological analysis of carbonate lithics. We show that the clustering of eruptive centers is controlled by tectonic features. A first order control is tentatively related to crustal laceration and deep magma injection along a ENE-trending Quaternary lateral tear in the slab and to Mesozoic rift-related normal faults. A second-order control is provided by orogenic structures (mainly thrust and extensional faults). In particular, magma-water explosive interaction occurred at multiple levels (< 2.3 km depth), depending on the structural and hydrogeologic setting of the Albian-Cenomanian carbonates, which are intersected by high-angle faults. The progressive comminution, rounding and whitening of entrained carbonate lithics allow us to trace multistage diatreme processes. Finally, our study bears implications on volcanic hazard assessment in the region
Initiation and development of the Pennine Basal Thrust (Swiss Alps): a structural and geochronological study of an exhumed megathrust
No full textThe Pennine Basal Thrust (PBT) is an exhumed megathrust developed during continental collision from late Eocene to Miocene. To trace its evolution, five samples, with indications for up to three microstructurally diachronous white-mica generations, were investigated by laser in-situ and step-heating Ar-40-Ar-39 dating. Three deformation-related crystallization ages can be distinguished: (1) D-1, characterized in the PBT hanging wall by an S-1 foliation defined by white mica + chloritoid, began at or before similar to 38.0 Ma; (2) D-2 formed a pervasive S-2 cleavage and synchronous white-mica rich veins dated at similar to 27 Ma; (3) D(3)produced an S-3 crenulation cleavage and chlorite + white-mica veins dated at similar to 23 Ma. Older ages of similar to 96 Ma (footwall) and similar to 115 Ma (hanging wall) are interpreted as minimum ages for the detrital component. Finally, discrete faulting produced fault gouge, with an illite K-Ar age of similar to 19 Ma. A simplified back-restored reconstruction provides a tectonic context for the dated structures. In this framework, D-1 occurred during middle to late Eocene tectonic accretion. After late Eocene initiation of continental collision, D-2 reflects Oligocene top-to-NW shearing, with both in- and out-of-sequence thrusting. D-3 then developed from 23 to 19 Ma during the progressive deactivation of the PBT
Understanding the origin and mixing of deep fluids in shallow aquifers and possible implications for crustal deformation studies. San Vittorino plain, Central Apennines
Full text linkExpanding knowledge about the origin and mixing of deep fluids and the water–rock–gas interactions in aquifer systems can represent an improvement in the comprehension of crustal deformation processes. An analysis of the deep and meteoric fluid contributions to a regional groundwater circulation model in an active seismic area has been carried out. We performed two hydrogeochemical screenings of 15 springs in the San Vittorino Plain (central Italy). Furthermore, we updated the San Vittorino Plain structural setting with a new geological map and cross-sections, highlighting how and where the aquifers are intersected by faults. The application of Na-Li geothermometers, coupled with trace element and gas analyses, agrees in attributing the highest temperatures (>150◦C), the greatest enrichments in Li (124.3 ppb) and Cs (>5 ppb), and traces of mantle-derived He (1–2%) to springs located in correspondence with high-angle faults (i.e., S5, S11, S13, and S15). This evidence points out the role of faults acting as vehicles for deep fluids into regional carbonate aquifers. These results highlight the criteria for identifying the most suitable sites for monitoring variations in groundwater geochemistry due to the uprising of deep fluids modulated by fault activity to be further correlated with crustal deformation and possibly with seismicity
Groundwater–rock interactions and mixing in fault–controlled karstic aquifers. A structural, hydrogeochemical and multi-isotopic review of the Pontina Plain (Central Italy)
Full text linkKarstic aquifers represent crucial water resources and are categorized as either stratigraphically or fault–controlled. This study investigates groundwater–rock interactions and mixing processes within one of the largest fault–controlled karstic aquifers in Central Italy, adjacent to the Pontina plain, which is a highly populated area where agricultural activities and climate change challenge the groundwater assessment of a complex aquifer. We conducted structural, hydrogeochemical, and multi-isotopic screening of ten selected springs with different degrees of mineralization (ranging from Ca–HCO3 to Na–Cl hydrofacies), incorporating new analyses and modeling of δ34S(SO4), δ18O(SO4), 87Sr/86Sr, and δ11B. Additionally, the reinterpretation of a seismic section provides a more detailed framework extending to depths of approximately 5–7 km that allows the identification of the geometry of normal faults, which act as pathways for upwelling fluids. Our findings reveal that hydrogeochemical compositions result from multiple interactions between karstic water and deeper fluids that have interacted with different rocks. Concentration (Na/Li) and isotope (SO4–H2O) geothermometers, coupled with geochemical modeling and trace element analysis, enabled the estimation of a water temperature equilibrium of approximately 95.5 °C, with Triassic evaporites generally corresponding to a depth of approximately 3 km and a temperature of 40 °C with magmatic rocks at approximately 1 km depth, which is likely associated with ongoing tectonics and the Quaternary tectonically controlled Volsci Volcanic Field. To obtain the latter estimate, we used a new geothermometer activity based on the equilibrium between analcime and pollucite. Furthermore, this multidisciplinary approach enhances the understanding of groundwater behavior in fault–controlled karstic aquifers, where mantle-derived CO2 dissolved in groundwater is the driving force behind water–rock interactions. Given the potential for further variations in mixing, which may worsen water quality and increase aquifer vulnerability, periodic monitoring of these processes is essential in a human-impacted environment amidst ongoing climate change
The anchimetamorphic tectonic mélange of Tempa Roccarossa (southern Apennines, Italy): insights on the kinematic and thermobaric evolution of the Upper Miocene-Pliocene orogenic wedge
No full textStudies of tectonic mélanges provide constraints on the evolution of active plate margins. However, resolving the pressure-temperature trajectories of these deformed rocks, which are exhumed from low-temperature conditions, can be challenging. We analyzed a Late Miocene-Early Pliocene tectonic mélange formed in a shear zone in the southern Apennines (Basilicata, Italy), located in the hanging wall of a regional thrust, to provide estimates of temperature, pressure and strain. The mélange comprises slates with a fine-grained phyllosilicate matrix embedding larger porphyroclasts with relict S0 bedding. Electronic microscope analysis revealed a disjunctive cleavage (S1), partially to fully transposed by a top-to-the-E/SE crenulation cleavage (S2) marked by white mica and chlorite. A late weak cleavage (S3) is not accompanied by newly formed minerals. Kinematic vorticity analysis indicates a range of 20%–35% coaxial strain, whereas 3D strain analysis of deformed clasts suggests oblate strain. X-Ray Powder Diffraction analysis of grains 2 μm are likely detrital and record higher pressure-temperature conditions. Assuming a regional paleogeothermal gradient of 20°C/km, we estimate a maximum burial depth of about 12 km and a pressure of 0.32 GPa. This approach can be applied to similar contexts worldwide, providing a tool for regional tectonic reconstruction and process-oriented studies
Segmentation of the Apenninic margin of the Tyrrhenian back-arc basin forced by the subduction of an inherited transform system
Full text linkThe Tyrrhenian back-arc basin developed at the rear of the E-ward migrating Apennine fold-and-thrust belt, with northward decreasing rollback of the subducting Adria slab leading to northward fading of back-arc extension. The northern portion of the Tyrrhenian basin is made of thinned continental crust, whereas in the central/southern portion extension eventually evolved to oceanic crust production. In this framework, a long-lasting debate concerns the existence of a >200 km long transform zone along the 41st parallel, which should separate the two portions of the Tyrrhenian basin. At its eastern termination, a branch of the presumed transform zone enters the Tyrrhenian margin of the Apennine belt and occurs as an accommodation zone made of a ribbon of extensional faults and related basins. This accommodation zone, which separates areas of mutually perpendicular extension directions, is here introduced, described, and named the Ponza-Alife accommodation zone. Interpretation of seismic lines and new structural and stratigraphic data from this accommodation zone have been used to constrain the pre-orogenic and syn-orogenic architecture of the subducting plate and the Plio-Quaternary back-arc extensional stage. Our data indicate that the studied zone retraces a deep-seated transform fault system located in the subducting plate and inherited from an Early Jurassic rifting episode, which caused the lateral juxtaposition of different rift domains in the subducting plate. We propose that during collision and trench retreat, this lateral juxtaposition has controlled differential retreat of the subducting plate across the studied zone, forcing the development of the Ponza-Alife accommodation zone in the overlying back-arc basin's margin
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