Mazzarini, Francesco

Monogenetic volcanic fields are present in different geo-tectonic settings (subduction, divergence and intraplate settings) consisting of tens to hundreds of volcanic constructs (cones, maars, fissures, small shields) that are the physical expression of distributed volcanism. Notably, the spatial distribution of the volcanic constructs in volcanic fields often shows a spatial clustering that is thought to be linked to shallow (i.e., crustal strain, structural inheritance) and deep processes (i.e., magma input, composition and rheology). Noteworthy, the spatial distribution of vents (cones, maars, fissures, small shields) is the final frame of the history of the volcanic field and does not provide information about its timeevolution. Consequently, when a vent spatial clustering is assessed for a particular volcanic field two questions remain unanswered: i) have the vents always been clustered during the life of the volcanic field? ii) If not, when did the clustering of vents begin? To answer these questions, the spatial distributions of vents along with their morphologic classification have been applied to volcanic fields located in an active tectonic and volcanic area. The northern Main Ethiopian Rift, being its geo-tectonic setting and its geologic evolution well known, is the locale where the time evolution of vent spatial clustering can be investigated. Spatial distribution and morphometric analysis of vents have been applied to three well known monogenetic volcanic fields (Debre Zeyt, Wonji and Kone) in the northern Main Ethiopian Rift. Vent clustering initiated when about 60% of the vents formed within each of the above mentioned fields. The Kone volcanic field show vent clustering since the beginning suggesting that, within a specific tectonic setting, vent clustering is favoured by crustal strain partitioning and associated volcanic activity.

The late Miocene Monte Capanne and Porto Azzurro plutons are investigated by means of coupled U-Pb zircon and 40Ar/39Ar white mica dating to test the occurrence of long-lived magmatic systems in the upper crust. Zircon crystallized for > 1 Myr in both plutonic systems, with supersolidus conditions overlapping for ~220 kyr indicating previously unrecognized co-existence of the two reservoirs. The development of the Porto Azzurro high T-aureole is post-dated by continuous igneous zircon crystallization until ~ 6.0 Ma. By linking crystallization to post-emplacement cooling of late-stage pulses in both western and eastern Elba we constrain long-lived sizeable reservoirs (possibly the same reservoir) in the Tyrrhenian upper crust between ~8 and 6 Ma.

between Elba Island and Monte Argentario promontory, was performed to reappraise the Tuscan shelf tectonic evolution. Despite the almost flat geometry of the seafloor, seismic profiles show a corrugated morphology of the pre-neogenic deformed acoustic basement, organized in structural highs and narrow, mostly N-S and NNW-SSE basins. We identified an intimate relationship between the thrust-related structural highs and the position of the basins, principally located at the forelimb and backlimb of major antiforms, a legacy of a primarily Miocene compressional stage. During the middle Miocene, the Tyrrhenian Sea opening set up, and the extensional front migrated from west to east, progressively activating and deactivating the observed high-angle faults, blandly controlling the sedimentation within the basins. After the late Messinian, a regional collapse stage led to the deepening and widening of the basins. A progressive deactivation of all the normal faults is recorded from the lower Pliocene. After the Late Pliocene/early Pleistocene, the area turned into a passive and widespread sinking stage without any frank tectonic activity. Results show that regional thrusts shaped the main architecture of the Tuscan Shelf shallow crust, while the neogenic depocenters started to develop as thrust-top basins along the flanks of the inherited antiforms. Intriguingly and partially in contrast with previous works, no evidence of lowangle normal fault was observed. We propose an innovative model that poses new questions on the crustal-scale mechanisms responsible for Tyrrhenian extensional process-related features, also establishing a new and unique starting point for fully unraveling the tectonic evolution of this portion of central Italy's offshore domain.

volcanic provinces with the largest shield volcanoes of the Solar System. However, volcanism on Mars is characterized also by the occurrence of broad volcanic fields, either in the form of small lava shields or monogenic volcanic cones. The region of Syria Planum (SP) is located east of the Tharsis province and between Noctis Labyrinthus to the North and Claritas Fossae to the southwest. It is an example of diffuse volcanism, presenting hundreds of small edifices (namely Syria Colles) which occur on top of a large bulge roughly 300 km × 200 km in size. SP exhibits a complex magmatic and volcano-tectonic evolution spanning from the early-Noachian to the more recent Amazonian. In this work, we investigate the geometry of the plumbing system of the SP volcanic field as well as the geometries of the volcanic constructs (i.e., vent elongation and vent alignment) that may be linked to the structures that fed the magma presenting a possible tectonic and volcanic evolution of the distributed volcanism phase in this area. The spatial distribution of vents and the overall map view shape of the volcanic field were studied in terms of vent clustering and spatial distribution. We show that the widespread and diffuse volcanism in SP presents clear vent clusters that are related to a deep source magma reservoir located at ~100 km depth. We also show that Syria Colles vent elongations and azimuth distributions suggest that the magma exploited the inherited regional structural framework, coherent with the Syria Colles late-stage Amazonian magmatic event, and highlighting the role of a shallow crustal tectonic framework in shaping the Martian volcanism.

Reply to the comment by Luca Bolognesi

The natural park of Le Biancane is located in the southern sector of the Larderello-Travale geothermal field (LTGF). It extends over an approximately 100,000 m2 area where the impermeable caprock is locally absent and deep fluids may directly reach the surface. Through a multidisciplinary approach including measurements of soil CO2 flux (total output of 11.5 t day􀀀 1), soil temperature (average 34.4 ◦C), stable isotope and chemical data on fluids from fumaroles (dominated by a mixture of geothermal gases and air or gases from air-saturated meteoric water), and structural analysis of the formation outcropping, we found that anomalous CO2 emissions are positively correlated with shallow temperature anomalies. These are in restricted locations adjacent to vents and fumaroles, where a network of well-connected fractures (preferentially NW-SE and NE-SW orientated and with steep dips) drains efficiently allowing upward migration of the deep fluids and the energy toward the surface.

The magmatic-tectonic evolution of the EARS has been accompanied, since the initial stages of crustal deformation, by the formation of volcanic structures that formed outside of the main rift depression and are described with the general term of flank or off-rift volcanism. In this contribution, six Quaternary off-rift volcanic fields, from southern Ethiopia to southern Kenya are studied in terms of their map view shape, vent distribution and volcanic structures and constructions. They are, from the North one: Mega, Hurry Hills, Marsabit, Nyambeni Hills, Mount Kenya and Chyulu Hills. These six Quaternary off-rift volcanic fields formed far (> 80 km) from the rift's main border faults and all have an elongated shape having their axis at a high angle to the nearly N-S southern Ethiopian and the nearly N-S trending Kenya rifts and to the transversal, roughly NW-SE-trending, preexisting Mesozoic Anza Graben. The shape, the spatial distribution of vents as well as the volcanic structures of the fields indicate that each volcanic field records the interaction between the magma dynamics, the crustal structural architecture and the local stress field. The volcanic fields are located at the border of a very cold and stiff lithosphere as inferred by geophysical data. In summary, the location and the evolution of the analysed off-rift volcanic fields are controlled by the inner structures of the EARS whereas their vent spatial distribution and shape are controlled by the local shallow structure of the crust and local stress field.

In recent decades, geological modeling has significantly evolved, relying on the growing potential of hardware and software to manage and integrate vast datasets of 2D-3D geophysical underground data. Therefore, digitization and integration with other forms of data can often improve understanding of geological systems, even when using so-called vintage or historical data. Seismic reflection data have been extensively acquired mainly for hydrocarbon exploration since the 60s generating large volumes of data. Typically, these data have been for private commercial use and are relatively unavailable for research. However, with time, large volumes of vintage seismic reflection data in many countries worldwide are now becoming publicly available through time-based de-classification schemes. Such data have a great potential for modern-day geo-research, unleashing opportunities to improve geological understanding through re-interpretation with modern methods. However, a downside of these vintage data is that they are often only available in analog (paper, raster) format. The vectorization of these data then constitutes an essential step for unlocking their research potential. In 2018 INGV established the SISMOLAB-3D infrastructure, which is mainly devoted to analyzing digital subsurface data, such as seismic reflection profiles and well-logs, to build 2D-3D geological models, principally for seismotectonics, seismic hazard assessment, and geo-resources applications. In this contribution, we discuss the robustness of the WIGGLE2SEGY code, firstly published by Sopher in 2018, focusing on examples from different tectonic and geodynamic contexts within Italian territory. We applied the SEG-Y conversion method to onshore and offshore raster seismic profiles related to ceased exploration permits, comparing the results with other published archives of SEG-Y data obtained from the conversion of vintage data. Such an approach results in digital SEG-Y files with unprecedented quality and detail. The systematic application of this method will allow the construction of a comprehensive dataset of digital SEG-Y seismic profiles across Italy, thereby expanding and sharing the INGV SISMOLAB-3D portfolio with the scientific community to foster innovative and advanced scientific analysis.

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.

Magmatic and sub-solidus fabrics in intrusive rocks are frequently used to infer the relative timing of deformation with respect to magma emplacement and cooling. Here, we describe the relationships between strain and fabric development in leucogranite sheets (pegmatite, aplite) emplaced into shear zones that localized post-thermal peak deformation in the contact aureole of an upper crustal pluton (<0.2 GPa) on the Island of Elba, Italy. The leucogranite sheets present igneous, mylonitic, and cataclastic fabrics. Detailed meso- and microscopic structural analysis suggests that the dykes emplaced in the shear zones behaved as competent, rigid bodies during mylonitic deformation of the host rocks. Thermal modelling indicates that emplacement and cooling of the sheets occurred very rapidly (a few days to years) compared to typical tectonic strain rates and strain accumulation timescales in the host rocks. Such a fast cooling does not allow melt or magma-induced thermal softening in the host rocks during deformation. The development of mylonitic and cataclastic fabrics in the dykes was controlled by the localized activation of fluid-controlled reaction softening mechanisms (mylonitic fabric) and embrittlement during cooling in sites of high-strain (cataclastic fabric). We show that a broad spectrum of fabrics can form in igneous sheet intrusions emplaced at the same time and crustal level. The coexistence of isotropic (non-foliated igneous) versus anisotropic (mylonitic and cataclastic) fabrics in igneous sheet intrusions should therefore be evaluated in terms of tectonic strain rates, cooling rates, thermal state of the host, distribution of heterogeneous strain, and activation of strain softening mechanisms. Our observations highlight that the concepts of pre-, syn-, late- and post-tectonic fabrics in intrusive igneous rocks should be used with caution when interpreting relative timing relationships between deformation and magmatism.