1,721,001 research outputs found
Pop-up structure in massive carbonate-hosted fold-and-thrust belt. Insight from field mapping and 2D kinematic model in the central Apennines
No full textFold-and-thrust belts are characterized by the occurrence of foreland-verging thrusts and antithetic backthrust, which develop in the hangingwall of thrust sheets. Both thrust and backthrust bound the so-called pop-up structure, which is a deformed zone characterized by thrust- and backthrust-related anticlines. Pop-up structures mainly develop in fold-and-thrust belts characterized by a multilayered sedimentary sequence, consisting of limestones, marls, and shales, deformed above a weak décollement, such as evaporites. However, in this work,
we combine field mapping, stratigraphic constrains, and structural analysis with 2D kinematic forward modeling to document a pop-up structure developed within limestones/dolostones, deformed above a strong décollement consisting of dolostones, in the central Apennines, Italy. In particular, we describe a SW-verging anticline and a NE-verging anticline in the SW and NE margin of the Serra Lunga ridge, respectively. Such folds were generated by a NE-dipping backthrust and by SW-dipping forethrust, respectively. Therefore, we suggest that the Serra
Lunga ridge represents a pop-up structure, showing geometries similar to other pop-up structures observed within fold-and-thrust belts characterized by a multilayered sedimentary sequence. In addition, backlimb tilting of backthrust-related anticlines generates the forelandward-dipping monoclines, observed within thrust sheets in the Central Apennines and in several fold-and-thrust belts worldwide
Structure, fluid flow and mechanical, properties of carbonate/clay-hosted seismogenetic faults: case studies from the Central Apennines, Italy
Full text linkIn many seismically active countries (e.g., Italy, Greece, Turkey, China, USA) moderate to large earthquakes nucleate in and propagate through heterogeneous (i.e., consisting of carbonate, marly, and clayey deposits) sedimentary successions within the brittle upper crust (< 5 km depth), often causing surface displacement with associated damages and casualities. In particular, in the central Apennines of Italy, moderate earthquakes (< Mw 7.0) propagate through the heterogeneous carbonatic-clayey sedimentary cover up to the Earth’s surface, possibly causing surface faulting (e.g., 1915, Mw 7.0, Avezzano Earthquake; 2009, Mw 6.3, L’Aquila Earthquake. For instance, the mainshock of the recent Mw 6.0 Amatrice earthquake of August 24th, 2016, nucleated at ~7-8 km depth and the seismic slip propagated upward through carbonate rocks causing a ~6 km long surface rupture and deformation. Indirect studies (i.e., through seismological, geophysical, and geodetic techniques) lack of sufficient spatio-temporal resolution to constrain the detailed three-dimensional fault-zone architecture, the deformation mechanisms, and the seismic-related fluid circulation within seismogenic faults at depth. The study of exposed fault zones exhumed from shallow depth (i.e., depths < 3 km) can narrow this knowledge gap and can help in understanding how the shallow fault zone structure can promote or inhibit seismic slip propagation up to the Earth’s surface. For these reasons, in this thesis, I used a multidisciplinary approach to study exposed carbonate/clay-hosted active faults, which can be reliable analogues of buried seismogenic faults at depth, in the seismogenic domain of the central Apennines, Italy. In particular, I combined fieldwork (geological mapping and structural analysis) with laboratory studies. I used optical microscopy and FESEM (Field Emission Scanning Electron Microscopy) to study fault rock microstructures from micro- to nanoscale. I used stable isotope analyses on calcite veins/cement, whole rock geochemistry, cathodoluminescence, and X-ray powder diffraction to study the origin and paleotemperatures of geofluids, which circulated in the fault zones, and fault rock mineralogy. I used low to high velocity friction experiments (using the Slow to High Velocity Apparatus, SHIVA, at INGV in Rome) to understand fault rock frictional properties during earthquake propagation and in situ mechanical analyses using Atomic Force Microscopy to understand fault rocks elastic properties (Young’s modulus and viscoelasticity) down to nanoscale. In particular, the main focus of this thesis is to understand the roles both of fluids and phyllosilicates during the seismic cycle within carbonate-hosted faults in the shallow carbonate-dominated brittle crust
Architecture and deformation mechanisms within a carbonate-hosted fault zone (Fucino basin)
No full textThe 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 one
A new methodology for paleostress reconstruction using theory, field observations and petrophysical data
No full textThe measurement of crustal stress magnitude is always challenging and generally poorly constrained. This is particularly significant in active fault zones where the knowledge of stress magnitude is crucial for understanding fault mechanics during earthquakes nucleation. In this work we propose a workflow using laboratory and field data as a proxy for quantitative paleostress reconstruction along active fault zone. We studied the exhumed Olevano-Antrodoco Thrust Fault (OATF) in Central Italy consisting of a SW-dipping thrust fault that juxtapose middle Miocene carbonates in the hangingwall above upper Miocene foredeep sandstones, W-SW-dipping, in the footwall. We collected 26 samples of footwall sandstones approaching progressively the OATF, from the undeformed deposits (1 km away to the E) to the tectonically deformed sandstones close (50 m far) to the OATF. Field data highlighted that the footwall sandstones dips towards W-SW, thus moving towards the OATF, shallower strata progressively crop out, hence from the stratigraphical point of view, porosity should increase due to the decreasing in burial depth. On the other hand laboratory measurements revealed the opposite. Using a permeameter we measured porosity, permeability, and P wave velocity both at ambient pressure and at increasing confining pressure up to 100 MPa, simulating an increase in burial depth up to 4 km. Porosity measured at ambient pressure decreases moving towards the OATF as well as permeability, whilst P wave velocity increased. P wave velocities obtained during depressurization from 100 MPa to ambient pressure were always higher than those recorded during pressurization suggesting inelastic compaction. In order to reconstruct the paleostresses we started from the Athy's exponential porosity-depth relationship. We calculate the initial porosity at the time of deposition for undeformed sandstones 1 km away from OATF (11.1%) Using stratigraphic and geometrical relationships we calculated that the maximum burial depth of sandstones close to the OATF was about 1500 m. We then calculated that the porosity of sandstones close to the OATF related only to sedimentary load was about 7.4 %. This value is higher than the present-day porosity that is 3.7%. The difference (Δφ = 3.7%, equal to inferred porosity minus measured porosity) is thought to be caused by the tectonic load and inelastic compaction associated with the activity of the OATF that changed permanently the petrophysical properties inherited from sedimentation and diagenesis as confirmed by laboratory measurements. The stress needed to reduce porosity from the theoretical value of 7.4% to the measured value of 3.7% at 1500 m depth, is 64.8 MPa. This value represents the maximum differential stress (Δσ) that acted close to the fault plane (tectonic load). Since field data indicated a compressional regime; this implies that the horizontal stress is σ1 and the vertical stress is σ3. By using the density-depth relationship, it resulted that, close to the OATF at a depth of 1500 m, σ3=37.7 MPa. Consequently, σ1, calculated as σ1=(σ3+Δσ), is 102.5 MPa. Assuming a coefficient of friction for sandstones of 0.71 and overburden-related inelastic compaction in the proximity of the fault plane, it results that the so calculated stresses are exactly the stress needed to reach critical conditions for slip. Since the OATF has more than 500 m of displacement, critical conditions for slip should have been maintained for long time; this strengthens our methodology that can thus be potentially applied for other tectonically deformed zones
Carbonate-clay mixing in cataclasite during fault activity
No full textNatural faults produce granular wear material, known as gouge or cataclasite, as a function of shear and grinding along the slipping surfaces. The characteristics of fault gouge have been studied extensively in the field, laboratory, and numerical simulations in order to gain a better understanding of fault mechanics (e.g., Marone and Scholz, 1989). However, observations of natural fault gouges in active fault zones can still provide precious information about fault activity and mechanical processes acting during fault evolution. Here, we report detailed microstructural observations (optical and electronic microscopy) on natural fault rocks from the scarp of an active fault in carbonate rocks: the Tre Monti fault, in the Lazio-Abruzzi Apennines. This area is one of the most seismic regions in the Mediterranean area (e.g., L’Aquila Earthquake, Mw 6.3, 2009). We revealed, for the first time in this area, the occurrence of very comminute localization zones enriched with exotic material mostly composed of clays of the smectite group, minor biotite/muscovite, quartz, feldspar and other minerals. Clay minerals completely enwrap carbonate particles (<10 μm) and thick clay rich zones show fluid-like structures, carrying small carbonate particles in them. Previous studies in this area considered fault cataclasites to be composed only of carbonate wear material, smeared from pure limestones exposed in the footwall of the faults (Agosta and Kirschner, 2003). Chemical analysis confirmed that allogenic material derives from smearing and infiltration from clay-rich sedimentary sequences (Orbulina Marls Fm. and Flysch deposits.), within the fault zone. Moreover geophysical and geological studies revealed that Orbulina Marls and Flysch deposits occur in the hangingwall of the Tre Monti fault, buried beneath Plio-Pleistocene continental deposits (Cavinato et al., 2002), this evidence confirms our observations. Using field and microstructural data is possible to reconstruct the long-term evolution of a fault. Lithological juxtaposition during time, along a fault plane, can change the mechanical properties and fault strength by mixing of different lithologies progressively involved during fault activity. This mixing could control different deformation mechanism and earthquake potential, both in terms of nucleation and propagation. Further experimental studies will be performed to characterized frictional properties of natural mixture of clay rich fault gouges
GEOMETRY AND KINEMATICS FROM A WSW–TRENDING DEXTRAL TRANSFER ZONE: THE TRE MONTI FAULT (CENTRAL APENNINES)
No full textThe Central Apennines are characterized by a direction of maximum stretching oriented NE-SW. Despite this extension is mostly accommodated by normal slip on NW-trending fault segments, several faults have different orientation. In this study we present a detailed structural and geological survey to define the kinematics and architecture of an exhumed fault zone in Mesozoic carbonates, the WSW–trending and 8 km long Tre Monti–Celano fault zone, both by field and remote sensed methods (e.g. satellite pictures, aerial images, digital earth model). The Tre Monti–Celano fault zone is the northern boundary of the Fucino Basin, an intramontane half-graben filled by Plio–Quaternary alluvial and lacustrine deposits located in the central part of the Apennines chain, which was formed in Upper Pliocene and in Quaternary time by the extensional tectonic activity. The main fault plane consists of SSE-dipping normal fault cutting lower to middle Cretaceous limestone in the footwall and upper Pliocene to middle Pleistocene lacustrine deposits and subaerial slope debris in the hangingwall. Kinematics indicators, fracture orientation, and geometry of fault splays along the fault zone recorded mainly dextral transtension movement. The main fault is splitted into smaller segments (from 700 m up to 2 km in length) arranged with dextral en-echelon geometry. Inversion of kinematics indicators on fault segments oriented respectively ENE-WSW, NE-SW and NNE-SSW indicate a direction of maximum extension oriented NE-SW, accordingly to the direction of the maximum regional extension. These data suggest that the Tre Monti fault zone acted as a dextral transfer zone between two left-stepping major normal faults, oriented NW–SE and characterized by normal or slightly dextral oblique slip: the Venere-Serrone Fault in the south-east and the Velino fault in the north-west. Detailed mapping along the fault zone allowed to recognize different types of fault rocks generated by different lithologies involved in deformation and different amount of fault displacements. Further work will focus on a microstructural-mineralogical and geochemical characterization of natural fault rock samples to understand the mechanism of deformation and the role of fluid within these processes
Fault zone evolution and fluid circulation within active extensional faults in carbonate rocks
No full textStructural and geochemical methods applied to the seismically-active extensional Tre Monti Fault (central Apennines, Italy) were used to develop a conceptual evolutionary model of seismic faulting with fluid involvement for shallow (≤ 3 km depth) extensional faults in carbonate rocks. The relative chronology of these structures was reconstructed through cross-cutting relationships and cathodoluminescence analyses. C- and O-isotope data from different generations of fault-related mineralizations show a shift from marine- to meteoric-derived fluid circulation during exhumation from 3 to ≤1 km depths and concurrent fluid cooling from ~68 to <35 °C. Between ~3 km and ~1 km depths, impermeable barriers within the sedimentary sequence created a semi-closed hydrological system, where marine-derived fluids circulated within the fault zone at temperatures between 60° and 75°C without any mixing with meteoric-derived fluids. During fault zone exhumation at depths ≤ 1 km and temperatures <35 °C, the hydrological circulation became open and meteoric-derived fluids progressively infiltrated and circulated within the fault zone. The presence of low-permeability clayey layers in the sedimentary sequence contributed to control the type of fluids infiltrating into the fault zone. These results can foster the comprehension of fault-related fluid circulation within seismogenic faults at shallow depths in carbonate rocks of other fold-thrust belts involved in post-collisional seismogenic extensional tectonics
Phyllosilicate injection along extensional carbonate-hosted faults and implications for co-seismic slip propagation. Case studies from the central Apennines, Italy
No full textWe document phyllosilicates occurrence along five shallow (exhumed from depths < 3 km) carbonate hosted
extensional faults from the seismically-active domain of the central Apennines, Italy. The shallow
portion of this domain is characterized by a sedimentary succession consisting of ~5-6 km thick massive
carbonate deposits overlain by ~2 km thick phyllosilicate-rich deposits (marls and siliciclastic sandstones).
We show that the phyllosilicates observed within the studied carbonate-hosted faults derived
from the overlying phyllosilicate-rich sedimentary deposits and were involved in the faulting processes.
We infer that, during fault zone evolution, the phyllosilicates downward injected into pull-aparts (i.e.,
dilational jogs) that were generated along staircase extensional faults. With further displacement
accumulation, the clayey material was smeared and concentrated into localized layers along the
carbonate-hosted fault surfaces. These layers are usually thin (a few centimeters to decimeters thick), but
can reach also a few meters in thickness. We suggest that, even in tectonic settings dominated by high
frictional strength rocks (e.g., carbonates), localized layers enriched in weak phyllosilicates can occur
along shallow fault surfaces thus reducing the expected fault strength during earthquakes, possibly
promoting co-seismic slip propagation up to the Earth's surface
Fault-controlled upwelling of low-T hydrothermal fluids tracked by travertines in a fold-and-thrust belt, Monte Alpi, southern apennines, Italy
No full text3D Discrete Fracture Network (DFN) models of damage zone fluid corridors within a reservoir-scale normal fault in carbonates. Multiscale approach using field data and UAV imagery
No full textWe combined structural data collected in the field and those obtained from a virtual outcrop model constructed from drone imagery, to perform Discrete Fracture Network (DFN) modelling and to characterize the fracture distribution within the damage zone of the low-displacement (∼50 m) carbonate-hosted Pietrasecca Fault (PF) (central Apennines, Italy). Both in the hanging wall and in the footwall damage zones, fractures are vertical and parallel to slightly oblique to the fault strike. Fracture length distributions in the footwall damage zone indicate a high degree of fracture maturity, while in the hanging wall damage zone they indicate a low degree of fracture maturity. Pervasive stylolitization in the hanging wall must have hindered the development of through-going fractures, favoring diffuse fracturing characterized by stylolite-bounded fractures. DFN models suggest that permeabilities are 1-2 orders of magnitude greater in the footwall damage zone than in the hanging wall damage zone. As permeability (10-12 to 10-15 m2) is comparable with those measured in large-displacement (up to 600 m) faults in carbonates, our results show that also damage zones accompanying carbonate faults with ∼50 m of displacement could be fracture corridors for efficient fluid flow within subsurface reservoirs. Therefore, we propose that jumps in subsurface permeabilities occurring in many carbonate fractured reservoirs could be associated with to the occurrence of high permeability fracture zones developed within damage zones of low-displacement faults. As the recent advancement in seismic imaging allow the recognition of faults with displacement in the order of a few tens of meters, reservoir geologists and engineers can apply results of this study to better model the subsurface flow pathways near low displacement faults in carbonate reservoirs
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