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  • 2020-2023  (3)
  • 1
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    Frictional controls on the seismogenic zone: Insights from the Apenninic basement, Central Italy (2022)
    Elsevier
    Details
    Publication Date: 2022-03-22
    Description: Crustal seismicity is in general confined within the seismogenic layer, which is bounded at depth by processes related to the brittle-ductile transition (BDT) and in the shallow region by fault zone consolidation state and mineralogy. In the past 10-15 years, high resolution seismological and geodetic data have shown that faulting within and around the traditional seismogenic zone occurs in a large variety of slip modes. Frictional and structural heterogeneities have been invoked to explain such differences in fault slip mode and behaviour. However, an integrated and comprehensive picture remains extremely challenging because of difficulties to properly characterize fault rocks at seismogenic depths. Thus, the central-northern Apennines provide a unique opportunity because of the integration of deep-borehole stratigraphy and seismic reflection profiles with high resolution seismological data and outcrop studies. These works show that seismic sequences are limited within the sedimentary cover (depth 〈 9-10 km), suggesting that the underlaying basement plays a key-role in dictating the lower boundary of the seismogenic zone. Here we integrate structural data on exhumed outcrops of basement rocks with laboratory friction data to shed light on the mechanics of the Apenninic basement. Structural data highlight heterogeneous and pervasive deformation where foliated and phyllosilicate-rich rocks surround more competent quartz-rich lenses up to hundreds of meters in thickness. Phyllosilicate horizons deform predominantly by folding and foliation-parallel frictional sliding whereas quartz-rich lenses are characterized by brittle signatures represented by extensive fracturing and minor faulting. Laboratory experiments revealed that quartz-rich lithologies have relatively high friction, μ ≈ 0.51, velocity-strengthening to neutral behaviour, and elevated healing rates. On the contrary, phyllosilicate-rich (muscovite and chlorite) lithologies show low friction, 0.23 〈 μ 〈 0.31, a marked velocity strengthening behaviour that increases with increasing sliding velocity and negligible rates of frictional healing. Our integrated approach suggests that in the Apenninic basement deformation occurs along shear zones distributed on thickness up-to several kilometres, where the frictionally stable, foliated, and phyllosilicate-rich horizons favour aseismic deformation and therefore confine the depth of major earthquake ruptures and the seismogenic zone.
    Description: Published
    Description: 117444
    Description: 2T. Deformazione crostale attiva
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    From Fossil to Active Hydrothermal Outflow in the Back‐Arc of the Central Apennines (Zannone Island, Italy) (2022)
    Wiley-AGU
    Details
    Publication Date: 2022-10-24
    Description: Post-orogenic back-arc magmatism is accompanied by hydrothermal ore deposits and mineralizations derived from mantle and crustal sources. We investigate Zannone Island (ZI), back-arc Tyrrhenian basin, Italy, to define the source(s) of mineralizing hydrothermal fluids and their relationships with the regional petrological-tectonic setting. On ZI, early Miocene thrusting was overprinted by late Miocene post-orogenic extension and related hydrothermal alteration. Since active submarine hydrothermal outflow is reported close to the island, Zannone provides an ideal site to determine the P-T-X evolution of the long-lived hydrothermal system. We combined field work with microstructural analyses on syn-tectonic quartz veins and carbonate mineralizations, X-ray diffraction analysis, microthermometry and element mapping of fluid inclusions (FIs), C, O, and clumped isotopes, and analyses of noble gases (He-Ne-Ar) and CO2 content in FIs. Our results document the evolution of a fluid system of magmatic origin with increasing mixing of meteoric fluids. Magmatic fluids were responsible for quartz veins precipitation at ∼125 to 150 MPa and ∼300°C–350°C. With the onset of extensional faulting, magmatic fluids progressively interacted with carbonate rocks and mixed with meteoric fluids, leading to (a) host rock alteration with associated carbonate and minor ore mineral precipitation, (b) progressive fluid neutralization, (c) cooling of the hydrothermal system (from ∼320°C to ∼86°C), and (d) embrittlement and fracturing of the host rocks. Both quartz and carbonate mineralizations show noble gases values lower than those from the adjacent active volcanic areas and submarine hydrothermal systems, indicating that the fossil-to-active hydrothermal history is associated with the emplacement of multiple magmatic intrusions.
    Description: Published
    Description: e2022GC010474
    Description: 1T. Struttura della Terra
    Description: 2T. Deformazione crostale attiva
    Description: 7T. Variazioni delle caratteristiche crostali e "precursori"
    Description: 9T. Geochimica dei fluidi applicata allo studio e al monitoraggio di aree sismiche
    Description: 2TR. Ricostruzione e modellazione della struttura crostale
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
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    Structural characterization and K–Ar illite dating of reactivated, complex and heterogeneous fault zones: lessons from the Zuccale Fault, Northern Apennines (2022)
    Egu-Copernicus
    Details
    Publication Date: 2022-09-01
    Description: We studied the Zuccale Fault (ZF) on Elba, part of the Northern Apennines, to unravel the complex deformation history that is responsible for the remarkable architectural complexity of the fault. The ZF is characterized by a patchwork of at least six distinct, now tightly juxtaposed brittle structural facies (BSF), i.e. volumes of deformed rock characterized by a given fault rock type, texture, colour, composition, and age of formation. ZF fault rocks vary from massive cataclasite to foliated ultracataclasite, from clay-rich gouge to highly sheared talc phyllonite. Understanding the current spatial juxtaposition of these BSFs requires tight constraints on their age of formation during the ZF lifespan to integrate current fault geometries and characteristics over the time dimension of faulting. We present new K–Ar gouge dates obtained from three samples from two different BSFs. Two top-to-the-east foliated gouge and talc phyllonite samples document faulting in the Aquitanian (ca. 22 Ma), constraining east-vergent shearing along the ZF already in the earliest Miocene. A third sample constrains later faulting along the exclusively brittle, flat-lying principal slip surface to 〈 ca. 5 Ma. The new structural and geochronological results reveal an unexpectedly long faulting history spanning a ca. 20 Myr time interval in the framework of the evolution of the Northern Apennines. The current fault architecture is highly heterogeneous as it formed at very different times under different conditions during this prolonged history. We propose that the ZF started as an Aquitanian thrust that then became selectively reactivated by early Pliocene out-of-sequence thrusting during the progressive structuring of the Northern Apennine wedge. These results require the critical analysis of existing geodynamic models and call for alternative scenarios of continuous convergence between the late Oligocene and the early Pliocene with a major intervening phase of extension in the middle Miocene allowing for the isostatic re-equilibration of the Northern Apennine wedge. Extension started again in the Pliocene and is still active in the innermost portion of the Northern Apennines. In general terms, long-lived, mature faults can be very architecturally complex. Their unravelling, including understanding the dynamic evolution of their mechanical properties, requires a multidisciplinary approach combining detailed structural analyses with dating the deformation events recorded by the complex internal architecture, which is a phenomenal archive of faulting and faulting conditions through time and space.
    Description: Published
    Description: 1327–1351
    Description: 1T. Struttura della Terra
    Description: JCR Journal
    Keywords: Fault Zone Architecture ; Brittle Fabrics ; Fault Evolution ; K-Ar ages ; Elba Island ; Northern Apennines ; 04.04. Geology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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