Barbara Belelli Marchesini

Sapienza University of Rome

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Co-Authors

Luca Menegon

University of Oslo

Jussi Mattila

Finnish Consulting Group (Finland)

Giulio Viola

University of Bologna

Eugenio Carminati

Sapienza University of Rome

Paolo Garofalo

University of Bologna

Francesca Prando

University of Plymouth

Stefano Tavani

University of Naples Federico II

Antonio Caracausi

Istituto Nazionale di Geofisica e Vulcanologia

Nicola Mondillo

University of Naples Federico II

Luca Aldega

Sapienza University of Rome

Cooperative Institutions

Istituto Nazionale di Geofisica e Vulcanologia

Sapienza University of Rome

University of Padua

ETH Zurich

University of Perugia

University of Naples Federico II

Terra

University of Palermo

National Research Council

University of Plymouth

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A natural example of fluid-mediated brittle-ductile cyclicity in quartz veins from Olkiluoto Island, SW Finland

EGU General Assembly Conference Abstracts (2017)

Barbara Belelli Marchesini Paolo Garofalo Giulio Viola Jussi Mattila Luca Menegon

Brittleness

Source

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Fluid-mediated, brittle-ductile deformation at seismogenic depth: Part I – Fluid record and deformation history of fault-veins in a nuclear waste repository (Olkiluoto Island, Finland)

Barbara Belelli Marchesini Paolo Garofalo Luca Menegon Jussi Mattila Giulio Viola

Abstract. The dynamic evolution of fault zones at the seismogenic brittle-ductile transition zone (BDTZ) expresses the delicate interplay of numerous physical and chemical processes that occur at the time of strain localization. Deformation and flow of aqueous fluids in these zones, in particular, are closely related and mutually dependent during cycles of repeating, transient frictional and viscous deformation. Despite numerous studies documenting in detail seismogenic faults exhumed from the BDTZ, uncertainties remain as to the role of fluids in facilitating deformation in this zone, particularly with regard to the mechanics of broadly coeval brittle and ductile deformation. We combine here structural analysis, fluid inclusion data and mineral chemistry data from synkinematic and authigenic minerals to reconstruct the temporal variations in P, T and bulk composition of the fluids that mediated deformation and steered strain localization in a strike-slip fault from the BDTZ. This is a fault formed within the Paleoproterozoic migmatitic basement of southwestern Finland, hosting in its core two laterally continuous quartz veins formed by two texturally distinct quartz types – Qtz I and Qtz II, where Qtz I is demonstrably older than Qtz II. Veins within the diffuse damage zone of the fault are infilled by Qtz I. Multi-scalar structural analysis indicates recurrent cycles of mutually overprinting brittle and ductile deformation. Fluid inclusion microthermometry and mineral pair geothermometry indicate that both quartz types precipitated from a fluid that was in a homogeneous state during the recurrent cycles of faulting, and whose bulk salinity was in the 0–5 wt % NaCleq range. The temperature of the fluid phase involved with the various episodes of initial strain localization and later reactivation changed with time, from c. 240 °C in the damage zone to c. 350 °C in the core during Qtz I precipitation to < 200 °C at the time of Qtz II crystallization. Fluid pressure estimates show an oscillation in pore pressure comprised between 160 and 10 MPa during the fault activity stages. Our results suggest significant variability in the overall physical conditions during the fault deformation history, possibly reflecting the interaction of several batches of compositionally similar fluids ingressing the dilatant fault zone at different stages of its evolution, each with specific T and P conditions. Initial, fluid-mediated embrittlement of the faulted rock volume generated a diffuse network of joint and/or hybrid/shear fractures in the damage zone, whereas progressive strain localization led to more localized deformation within the fault core. Localization was guided by cyclically increasing fluid pressure and transient embrittlement of a system that was otherwise at overall ductile conditions. Our analysis implies that fluid overpressure at the brittle-ductile transition can play a key role in the initial embrittlment of the metamorphic basement and strain localization mechanisms.

Brittleness

Authigenic

Deformation mechanism

Overprinting

10.5194/se-2019-5

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Structural control on the alteration and fluid flow in the lithocap of the Allumiere-Tolfa epithermal system

Journal of Structural Geology (2023)

Barbara Belelli Marchesini Stefano Tavani Marco Mercuri Nicola Mondillo Mattia Pizzati

Zones of advanced argillic alteration with general low permeability (i.e., lithocaps) are common place in the shallow parts of porphyry and epithermal ore deposits and active geothermal systems. The study of structural control on alteration distributions is of paramount importance for exploitation purposes as it really influences the caprock efficiency. We present the results of a structural-mineralogical study carried out in the lithocap of the Allumiere-Tolfa epithermal system (Northern Apennines). We characterized the composition, textures and physical properties (i.e., in-situ permeability; relative rock strength) of alteration facies. We then integrated field structural analysis with analysis of a virtual outcrop model to reconstruct the geometry of principal fluid-corridors. It resulted that advanced argillic alteration was promoted by circulation of highly reactive fluid(s) along a complex network of NE- and NW-striking faults and fractures dissecting the acidic volcanic dome. Such structures likely developed in response to a local disturbance of the regional stress field due to the extrusion of the Tolfa dome, which controlled the syn-extensional mineralization of the Allumiere-Tolfa area.

Caprock

Outcrop

10.1016/j.jsg.2023.105035

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The role of fluids on strain localization at seismogenic depth: a case study from brittle-ductile faults from Olkiluoto Island, SW Finland

Barbara Belelli Marchesini Giulio Viola Luca Menegon Jussi Mattila Gunnar Schwarz

Fluids play a key role in weakening rocks, controlling crustal deformation from early fracture development to mature strain localization, fault nucleation and propagation through cumulative slip. In particular, at the brittle-ductile transition zone crustal deformation and fluid flow are mutually interconnected by repeating cycles of transient frictional and viscous deformation. Uncertainties remain, however, on the details of the micromechanical and chemical influence of fluids in facilitating strain localization processes.N-S to NW-SE sub-vertical brittle-ductile faults cut across the Paleoproterozoic migmatitic basement of southwestern Finland on the island of Olkiluoto, where the Finnish authorities plan the construction of a deep repository for high-grade nuclear waste. The faults are characterized by a brittle&#8211;ductile to fully brittle deformation style resulting from transient fluid pressurization. We investigated a representative fault by combining field and microstructural observations with fluid inclusion and mineral chemistry analysis on synkinematic and authigenic minerals in order to reconstruct the temporal variations of pressure, temperature, composition and salinity of the synkinematic fluids that controlled strain localization. Combined laser ablation inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-TOFMS) and electron back-scattered diffraction analysis (EBSD) were also applied on authigenic sulphides to gain insights into their role upon strain accommodation and deformation-induced elemental transport and distribution at the microscopic scale.Initial embrittlement of the Olkiluoto basement occurred under a first event of fluid overpressure conditions (> 210 MPa) with formation of a diffuse network of joints and/or hybrid&#8211;shear fractures in a volume that corresponds to the fault damage zone. Subsequent deformation was caused by repeated hydrofracturing induced by fluid pressure up to 210 MPa. Brittle ruptures affected a system that was otherwise under overall ductile conditions, as demonstrated by mutually overprinting veining, cataclasis and plastic deformation.Later exhumation and cooling of the fault system to fully brittle conditions was aided by reactivation triggered by a distinct fluid ingress at lower pressure (140-180 MPa) and temperature (&#8804; 300&#176; C). Deformation was accommodated at that stage by the interplay of brittle fracturing and low-temperature crystal-plastic in sulphides. Strain and fluid flow created high diffusivity pathways within the pyrite crystal lattices contributing to- and enhancing the net transport of a significant range of heavy elements (e.g. Co, Ni, Cu, Sn, Ag, As, Sb, Pb). These data indicate that the studied fault zone acted as a chemically open system and fault valve.

Brittleness

Authigenic

Cataclastic rock

10.5194/egusphere-egu2020-1134

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Caprock Genesis in Hydrothermal Systems via Alteration‐Controlled Fault Weakening and Impermeabilization

Journal of Geophysical Research Solid Earth (2025)

Barbara Belelli Marchesini Giacomo Pozzi Cristiano Collettini Eugenio Carminati Telemaco Tesei

Abstract The mechanical and hydraulic behavior of faults in geothermal systems is strongly impacted by fluid‐induced alteration. However, the effect of this alteration on fault properties in geothermal reservoirs is under documented. This affects our ability to model the properties of subsurface structures, both in reservoirs and caprocks, and potential hazards during geothermal exploitation. We investigated fault rocks from the caprock of a fossil hydrothermal system in the Apennines of Italy. We combined field structural observations with mineralogical and microstructural analyses of faults that guided the circulation of hydrothermal fluids and steered the caprock formation. We also performed friction experiments and permeability tests on representative fault rocks. We document fault weakening induced by the effect of hydrolytic alteration leading to the enrichment of clay minerals along the slip surfaces of major faults. Alunite‐clay‐rich rocks are much weaker (friction coefficient 0.26 < μ < 0.45) than the unaltered protolith (trachyte, μ = 0.55), favoring strain localization. The late‐stage enrichment of clays along faults induces a local decrease in permeability of three orders of magnitude (1.62 × 10 −19 m 2 ) with respect to the surrounding rocks (1.96 × 10 −16 m 2 ) transforming faults from fluid conduits into barriers. The efficiency of this process is demonstrated by the cyclic development of fluid overpressure in the altered volcanic rocks, highlighted by chaotic breccias and hydrofracture networks. Permeability barriers also enhance the lateral flow of hydrothermal fluids, promoting the lateral growth of the caprock. Velocity‐strengthening frictional behavior of alunite‐clay‐rich rocks suggests that hydrolytic alteration favors stable slip of faults at low temperature.

Caprock

10.1029/2024jb030565

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Strain-induced trace element mobility in a quartz-sulphide vein system: An example from the ONKALO™ spent nuclear fuel repository (Olkiluoto, SW Finland)

Journal of Structural Geology (2021)

Barbara Belelli Marchesini Luca Menegon Gunnar Schwarz Christoph Neff Peter Keresztes Schmidt

Trace element

Strain partitioning

10.1016/j.jsg.2021.104473

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Citations (3)

Tracing a mantle component in both paleo and modern fluids along seismogenic faults of southern Italy

Authorea (Authorea) (2024)

Filippo Zummo Fabrizio Agosta Antonio M. Álvarez‐Valero Andrea Billi Dario Buttitta

Aiming at understanding the source of the fluids that mineralizing within seismically active fault zones, we study the noble gas isotopes (i.e. helium (He), neon (Ne) and argon (Ar)) in the fluid inclusions (FIs) within the calcite veins sampled along high-angle fault zones of the Contursi hydrothermal basin, southern Italy. The latter basin lies in close vicinity of the MW = 6.9, 1980 Irpinia earthquake and exposes numerous fault scarps dissecting Mesozoic shallow-water carbonates. The isotopic analyses are conducted to identify the origin of the volatiles circulating along the faults at the time of calcite precipitation. Then, outcomes of this discussions are compared with currently outgassing of deep-sourced CO2 coupled to mantle-derived He is in that area, whose output is larger than those from some volcanic areas worldwide. The results indicate that He in FIs is dominated by a crustal radiogenic component (4He), and by an up to 20% of a mantle-derived component (3He), with a highest isotopic signature of 1.38 Ra. This value is consistent with the highest percentage of mantle He associated to CO2 high-flux emission in the investigated area (1.41 Ra). The variability of the He isotopic signature in FIs can result from either pre-or-post trapping processes and seismic activity that modify the pristine He isotopic signature (i.e. derived from the crust and/or mantle) in groundwater along the faults during periods of background seismicity. Such investigations are fundamental to understand fluid migration in fault systems and the role of fluids in processes of earthquake nucleation.

Radiogenic nuclide

Isotopic signature

10.22541/au.172495365.51392389/v1

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The role of fluids on strain localization at the base of the seismogenic crust: a case study from the Olkiluoto deep nuclear waste repository, southwestern Finland

Barbara Belelli Marchesini

This study focuses on the detailed investigation of the role played by fluids in triggering and controlling transient and repeated fluctuations between the frictional and viscous deformation end-members at the brittle-ductile transition zone (BDTZ) of the continental crust. Faults exhumed from the BDTZ and exposed in the Olkiluoto high-grade nuclear waste repository were studied combining field and microstructural observations with fluid inclusions and mineral pair geothermometry on fault minerals to reconstruct the temporal variations in fluid pressure, temperature and composition of the synkinematic fluids. Combined LA-ICP-TOFMS and EBSD analysis were also applied on authigenic sulphides to gain insights into their role upon strain accommodation and deformation-induced elemental transport at the microscopic scale. Faulting initiated as a consequence of a first event of fluid overpressure (Pf > 210 MPa) with the formation of a diffuse network of joints and hybrid–shear fractures. Cyclical brittle and ductile shearing followed, triggered by repeated hydrofracturing induced by a fluid pressure up to 210 MPa under overall ductile environmental conditions, demonstrated by mutually overprinting veining, crystal-plastic deformation and cataclasis. Later exhumation and cooling of the fault system to fully brittle conditions was aided by reactivation triggered by a distinct fluid ingress at lower pressure (140-180 MPa) and temperature (≤ 300° C). Deformation was accommodated at that stage by the interplay of brittle fracturing and low-temperature crystal-plasticity in sulphides. Strain and fluid flow created high diffusivity pathways within the pyrite crystal lattices contributing to- and enhancing the net transport of a significant range of heavy elements (e.g. Co, Ni, Cu, Sn, Ag, As, Sb, Pb). These data indicate that the studied fault acted as a chemically open system and fault valve. Hydrofracturing and their association with pseudotachylite-bearing faults suggest that fluid-mediated deformation may represent the record of the seismic cycle in the studied fault system.

Cataclastic rock

Brittleness

Shearing (physics)

Overpressure

Source

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Tracing a Mantle Component in Both Paleo and Modern Fluids Along Seismogenic Faults of Southern Italy

Geochemistry Geophysics Geosystems (2024)

Filippo Zummo Fabrizio Agosta Antonio M. Álvarez‐Valero Andrea Billi Dario Buttitta

Abstract Aiming at understanding the source of the fluids that mineralizing within seismically active fault zones, we investigate the noble gas isotopes (i.e., helium (He), neon (Ne), and argon (Ar)) in the fluid inclusions (FIs) trapped in the calcite veins sampled along high‐angle fault zones of the Contursi hydrothermal basin, southern Italy. The latter basin lies in close vicinity of the M W = 6.9, 1980 Irpinia earthquake and exposes numerous fault scarps dissecting Mesozoic shallow‐water carbonates. The analyses of noble gases (He, Ne, Ar) are conducted to identify the origin of the volatiles circulating along the faults at the time of calcite precipitation. Then, outcomes of this discussions are compared with currently outgassing of deep‐sourced CO 2 coupled to mantle‐derived He in that area, whose output is larger than those from some volcanic areas worldwide. The results indicate that He in FIs is dominated by a crustal radiogenic component ( 4 He), and by an up to 20% of a mantle‐derived component ( 3 He), with a highest isotopic signature of 1.38 Ra. This value is consistent with the highest percentage of mantle‐derived He associated to high‐flux CO 2 gas emission in the investigated area (1.41 Ra). We propose that the variability of the He isotopic signature measured in primary FIs can result from early trapping of fluid inclusions or post trapping processes and seismic activity that modify the pristine He isotopic signature (i.e., derived from the crust and/or mantle) in groundwater along the faults during periods of background seismicity. Such investigations are fundamental to understand fluid migration in fault systems and the role of fluids in processes of earthquake nucleation.

Tracing

Component (thermodynamics)

10.1029/2024gc011816

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Citations (1)

Structurally controlled kaolinite-alunite mineralization in the lithocap of a fossil geothermal system

Barbara Belelli Marchesini Stefano Tavani Marco Mercuri Luca Aldega Nicola Mondillo

Geothermal heat is a crucial source of renewable energy. Its present and future exploitation can be enhanced by the understanding of the in–situ structural and mineralogical processes and of how these processes may change the reservoir productivity.  Fossil hydrothermal system may thus be used as analogues to study in-situ fluid-rock interaction processes in active geothermal systems.We present the results of a structural-mineralogical study carried out in the lithocap of the Allumiere high-sulphidation epithermal system (Tolfa Mountains district, northern Latium, Italy). We integrated measurements of attitude of faults and fractures from field analysis with a virtual outcrop model constructed from drone imagery to model the distribution of major faults at the scale of the entire quarry. We then characterized the textures and mineralogical compositions of the alteration facies using optical petrography, Scanning Electron Microscope (SEM), X-ray diffraction analysis and field-based short-wave infrared (SWIR) spectrometer and we mapped their distribution in relation to major faults orientation.We interpreted that initial argillization was promoted by circulation of highly reactive fluid(s) along a major fluid conduit, probably in the form of a network of fault and fractures. Fluid circulation promotes hydrolytic alteration of the Plio-Quaternary pyroclastic rocks, forming a highly silicified carapace at the immediate vicinity of conduits. Enrichment in alunite and kaolinite increases towards distal areas, which in turn fades out into illite-smectite-bearing zone, where the country rock appears less altered.  Latest fracturing and fluid circulation occurs along two major sets of faults, oriented NE-SW and NW-SE that sharply put in contact different mineralogical facies.We propose that initial alteration induces a mineralogical-mechanical zonation that control latest reactivations of the system. Strain localization promotes a massive mineralization of alunite and kaolinite by continuous dissolution and precipitation along major faults.

Alunite

Illite

10.5194/egusphere-egu23-15099

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