Stable isotope geochemistry and structural elements of the Sabina region (Central Apennines, Italy)

Abstract

Various tectonic features are present in the Meso‐Cenozoic basin units of the Sabina region (Central Apennines, Italy): Mio‐Pliocene northeasterly verging thrusts are followed by Plio‐Pleistocene, N‐S oriented right‐lateral strike‐slip faults. Stable isotope geochemistry and examination of meso‐ and microstructures show that strain conditions differed through the course of tectonic history. Carbon and oxygen isotope analyses of the calate‐filled extensional fractures, the sigmoidal veins present between stylolitic cleavage surfaces, and fault plane surfaces with differing motion, demonstrate those different geneses. The “C/'” C of the older calcite‐filling fractures (present both in the thrust and the strike‐slip systems) suggests a deposition from shallow, fresh water circulation. Furthermore, the calcite fill of en echelon systems, that occur in the southernmost Plio‐Pleistocene units, is clearly the result of a more recent, right‐lateral strike‐slip movement, connected with shallow water circulation within Mesozoic limestones. The sigmoidal vein fills are derived from solid‐state pressure solution processes which were the result of strike‐slip movement. The deformation pattern related to the older thrust system is similar, but less intense; this also demonstrates general recrystallization processes in a closed system. This suggests that the total shortening of the deformed sections is lower than that obtained on the basis of solution on stylolitic planes, because a sigruficant volume of dissolved carbonates remained in the system. Stable isotope analysis also confirms that the deformational history of strongly cleaved rocks in the Sabina region took place in two phases and that extensional fractures formed before stylolithic planes, as suggested by structural and field observations.

Spatial-Temporal Evolution of Extensional Faulting and Fluid Circulation in the Amatrice Basin (Central Apennines, Italy) During the Pleistocene

“…Meteoric waters infiltrated downward into the tectonic cracks and were channelized through structural conduits within the rock volume, compatible with a scenario of tectonically maintained vertical permeability (e.g., Sibson, 2000;Cox et al, 2001;Rowland and Sibson, 2004). Similar scenarios of fluidassisted tectonic deformation in the central Apennines have been documented in faulted carbonate rocks (e.g., Maiorani et al, 1992;Conti et al, 2001;Ghisetti et al, 2001;Agosta et al, 2008;Smeraglia et al, , 2018, suggesting the interplay between transient permeability at the fault damage zones and mixing of fluids from different reservoirs (meteoric, groundwater, subcrustal). Noteworthy, the AFS provide a case history of fluid-rock interaction in siliciclastic units affecting by extensional faulting.…”

Late Pleistocene depositional cycles of the Lapis Tiburtinus travertine (Tivoli, Central Italy): Possible influence of climate and fault activity

“…The location of earthquake foci defines a NNW-striking fault zone seismically active between about 1.5 and 0.5 km of depth beneath the Lapis Tiburtinus travertine (Gasparini et al, 2002). Previous structural studies (Mattei et al, 1986;Maiorani et al, 1992;Faccenna et al, 1994a,b,c;Sagnotti et al, 1994;Billi et al, 2006b) showed that this fault and the associated brittle deformation are well exposed toward the north in the Jurassic-Miocene marine carbonate strata of the Cornicolani Mountains (Fig. 1).…”

“…The thermal waters eventually rise along active faults and emerge in the Acque Albule basin (Figs. 1 and 2) with an average temperature of 23°C and pH values between 6.0 and 6.2 (Manfra et al, 1976;Capelli et al, 1987;Pentecost and Tortora, 1989;Maiorani et al, 1992;Pentecost, 1995;Billi et al, 2006b). The complete chemical composition of these waters is provided by Giggenbach et al (1988) and Minissale et al (2002).…”

“…Calcite and sulfate precipitates are frequent over the fault surfaces and within the joints, where evidence of multiple cycles of precipitation have been observed. Isotope analyses on these precipitates showed that the originating fluids were of mixed nature, including meteoric waters combined with some deeper fluids that originated from or interacted with thermally-active volcanic bodies (Maiorani et al, 1992;Billi et al, 2006b).…”

Groundwater flow and geochemical modeling of the Acque Albule thermal basin (Central Italy): a conceptual model for evaluating influences of human exploitation on flowpath and thermal resource availability

“…In the Acque Albule area, tectonics led to the formation of a pull-apart subsiding basin characterized by a north-striking, right-lateral, seismically-active fault system and N40°E-N60°E extensional structures. The fault system is partially overburdened by travertine deposits and crops out in the carbonate Cornicolani Mountains (Maiorani et al 1992;Faccenna et al 1994;Sagnotti et al 1994;Gasparini et al 2002;Florindo et al 2004;Billi et al 2006;Faccenna et al 2008;Petitta et al 2011;Carucci et al 2012).…”