Marco Bonini - Academia.edu (original) (raw)

Papers by Marco Bonini

1] We present a comparison between numerical and analogue models focusing on the role of inherite... more 1] We present a comparison between numerical and analogue models focusing on the role of inherited lithospheric structures in influencing the process of continental break-up. Our results highlight that the presence of pre-existing anisotropies localizes strain and favors continental break-up and formation of a new ocean. For a fixed strain rate, the pre-rift lithosphere configuration influences rift duration, melt production and width and symmetry of the continental margin pair. Model results show a mainly two-phase tectonic history from continental extension to oceanization. In the first phase extension affects contemporaneously the whole rift structure, while in the second phase asthenosphere upwelling occurs into punctiform regularly-spaced spots sequentially propagating in an extension-orthogonal direction.

We examine the tectonic evolution and structural characteristics of the Quaternary intermontane M... more We examine the tectonic evolution and structural characteristics of the Quaternary intermontane Mugello, Casentino, and Sansepolcro basins, in the Northern Apennines fold-and-thrust belt. These basins have been classically interpreted to have developed under an extensional regime, and to mark the extensioncompression transition. The results of our study have instead allowed framing the formation of these basins into a compressive setting tied to the activity of backthrust faults at their northeastern margin. Syndepositional activity of these structures is manifested by consistent architecture of sediments and outcrop-scale deformation. After this phase, the Mugello and Sansepolcro basins experienced a phase of normal faulting extending from the middle Pleistocene until Present. Basin evolution can be thus basically framed into a two-phase history, with extensional tectonics superposed onto compressional structures. Analysis of morphologic features has revealed the occurrence of fresh fault scarps and interaction of faulting with drainage systems, which have been interpreted as evidence for potential ongoing activity of normal faults. Extensional tectonics is also manifested by recent seismicity, and likely caused the strong historical earthquakes affecting the Mugello and Sansepolcro basins. Qualitative comparison of surface information with depth-converted seismic data suggests the basins to represent discrete subsiding areas within the seismic belt extending along the axial zone of the Apennines. The inferred chronology of deformation and the timing of activity of normal faults have an obvious impact on the elaboration of seismic hazard models.

Analogue models were employed to investigate continental collision addressing the roles of (1) a ... more Analogue models were employed to investigate continental collision addressing the roles of (1) a suture zone separating different crustal blocks, (2) mid-crustal weak layers and (3) mantle strengths. These models confirmed that low-amplitude lithospheric and crustal buckling is the primary response to shortening with a wavelength mainly controlled by the strong upper crust and/or lithospheric mantle. With increasing shortening, bivergent thrusts formed across the brittle layers (equivalent to upper crust) at inflection points of the buckles while ductile layers (lower crust and mantle) continued being folded. The resulting geometries displayed pop-ups and pop-downs above the boundaries (sutures) between blocks. Further shortening led to wider, thrust-bounded deformation zones (A-belts) in front of the stronger blocks identified as beffective indentersQ. During shortening upward extrusion into A-belts allowed exhumation of deep material. Weak layers enhanced strain localisation. These modelling results have similarity in large-scale structures of modern orogens and are relevant to the understanding of natural collisional processes. D

REvISIon of SEISMIC hAzARd In EMILIA-RoMAGnA bASEd on A nEW SEISMoGEnIC zonAtIon of thE noRthERn APEnnInES

The high pCO 2 Caprese Reservoir (Northern Apennines, Italy): Relationships between present-and paleo-fluid geochemistry and structural setting

It has been noted since the mid 1800s that the Michelangelo's David, the standing marble male nud... more It has been noted since the mid 1800s that the Michelangelo's David, the standing marble male nude representing a masterpiece of the Italian Renaissance, is affected by small cracks on both legs that threaten its stability. Understanding the characteristics and the conditions under which these lesions developed is thus critical for the preservation of this universal masterpiece. In this study, we use an analogue modelling approach to test the conditions that led to the development of fractures in the David's legs and to get insights into its stability. Small-scale (10 cm-high) gypsum replicas of the statue were deformed in a centrifuge, where the models were affected by a body force stronger than gravity but otherwise playing the same role. Analysis of the model results suggests that both the stability and the resulting deformation of the statue are highly sensitive to its attitude. A forward inclination promotes destabilization: the higher the angle of inclination (˛), the more unstable the statue becomes under its own weight, confirming existing FEM modelling. In a vertical position, rupture of the statue typically occurs in the lower portions of the legs, but ruptures tend to develop progressively higher along the legs as ˛ increases. Comparison of these results with the lesions detected on the actual David suggests that a long-lasting, small forward inclination (likely close to ∼ 5 • ) of the statue may have represented a critical driving factor for the development of the observed damages.

Pre-eruptive ground deformation of Azerbaijan mud volcanoes detected through satellite radar interferometry (DInSAR)

ABSTRACT Mud volcanism is a process that leads to the extrusion of subsurface mud, fragments of c... more ABSTRACT Mud volcanism is a process that leads to the extrusion of subsurface mud, fragments of country rocks, saline waters and gases. This mechanism is typically linked to hydrocarbon traps, and the extrusion of this material builds up a variety of conical edifices with a similar morphology to those of magmatic volcanoes, though smaller in size. The Differential Interferometry Synthetic Aperture Radar (DInSAR) technique has been used to investigate the ground deformation related to the activity of the mud volcanoes of Azerbaijan. The analysis of a set of wrapped and unwrapped interferograms, selected according to their coherence, allowed the detection of significant superficial deformation related to the activity of four mud volcanoes. The ground displacement patterns observed during the period spanning from October 2003 to November 2005 are dominated by uplift, which reach a cumulative value of up to 20 and 10 cm at the Ayaz-Akhtarma and Khara Zira Island mud volcanoes, respectively. However, some sectors of the mud volcano edifices are affected by subsidence, which might correspond to deflation zones that coexist with the inflation zones characterized by the dominant uplift. Important deformation events, caused by fluid pressure and volume variations, have been observed both (1) in connection with main eruptive events in the form of pre-eruptive uplift, and (2) in the form of short-lived deformation pulses that interrupt a period of quiescence. Both deformation patterns show important similarities to those identified in some magmatic systems. The pre-eruptive uplift has been observed in many magmatic volcanoes as a consequence of magma intrusion or hydrothermal fluid injection. Moreover, discrete short-duration pulses of deformation are also experienced by magmatic volcanoes and are repeated over time as multiple inflation and deflation events.

Indizi di episodi compressivi Pleistocenici nell'Apennino settentrionale. Dati preliminari

The Vicano-Cimino Volcanic District (VCVD) is related to the post-orogenic magmatic activity of t... more The Vicano-Cimino Volcanic District (VCVD) is related to the post-orogenic magmatic activity of the peri-Tyrrhenian sector of Central Italy. The chemical and isotopic compositions of 333 water discharges and 25 gas emissions indicate the occurrence of two main sources: 1) cold Ca-HCO 3 to Ca(Na, K)-HCO 3 type waters from relatively shallow aquifers hosted in volcanic and sedimentary formations; and 2) thermal Ca-SO 4 (HCO 3 ) type waters located in a deep CO 2 -pressurized reservoir, hosted in carbonate-evaporite rocks and separated from the shallow aquifers by thick sequences of low-permeability formations. Carbon dioxide is mainly produced by thermal metamorphic decarbonation within the deepest and hottest parts of the carbonate-evaporite reservoir (δ 13 C-CO 2 from −3.1 to +2.2‰ vs. VPDB), likely affected by a mantle-rooted CO 2 . Release of CO 2 -rich gases from the deep aquifer into the overlying shallow aquifers produces high-CO 2 springs and bubbling pools. The spatial distribution of thermal waters and CO 2 -rich cold discharges is strongly controlled by fractures and faults located in correspondence with buried structural highs. Stable isotopes (δD and δ 18 O) suggest that meteoric water feeds both the shallow and deep reservoirs. The relatively low R/R a values (0.27-1.19) indicate that He is mainly deriving from a crustal source, with minor component from the mantle affected by crustal contamination related to the subduction of the Adriatic plate. Consistently, relatively high N 2 /Ar and N 2 / 3 He ratios and positive δ 15 N-N 2 values (from 0.91 to 5.7‰ vs. air) characterize the VCVD gas discharges, suggesting the occurrence of a significant "excess" nitrogen. Isotopic compositions of CH 4 (δ 13 C-CH 4 and δD-CH 4 values from −28.9 to −22.1‰ vs. VPDB and from −176 to −138‰ vs. VSMOW, respectively), and composition of light alkanes are indicative of prevalent thermogenic CH 4 , although the occurrence of abiogenic CH 4 production cannot be excluded. The δ 34 S-H 2 S values (from +9.3 to +11.4‰ vs. VCDT) are consistent with the hypothesis of H 2 S production from thermogenic reduction of Triassic anhydrites. Gas geothermometry in the H 2 O-H 2 -Ar-H 2 S system suggests that the VCVD gases equilibrated in a liquid phase at redox conditions controlled by interactions of fluids with the local mineral assemblage at temperatures lower (b200°C) than that and measured in deep (N2000 m) geothermal wells. This confirms that secondary processes, i.e. steam condensation, gas dissolution in shallow aquifers, re-equilibration at lower temperature, and microbial activity, significantly affect the chemistry of the uprising fluids. Thermal water chemistry supports the occurrence in this area of an anomalous heat flow that, coupled with the recent demographic growth, makes this site suitable for direct and indirect exploitation of the geothermal resource, in agreement with the preliminary surveys carried out in the 1970's-1990's for geothermal exploration purposes.

The inner Northern Apennines (western Tuscany and Tyrrhenian basin) is characterized by a relativ... more The inner Northern Apennines (western Tuscany and Tyrrhenian basin) is characterized by a relatively thin continental crust (∼20-25 km), high heat flow (>100 mW m −2 ), and the presence of relevant tectonic elision of stratigraphic sequences, a setting known as Serie Ridotta. These features are normally ascribed to an extensional deformation that affected the back-arc area above the subducting Adria plate since the Early-Middle Miocene (∼16 Ma). However, various geophysical studies image the continental crust to be currently affected by W-dipping thrust faults (and associated basement uplifts) that have not been obliterated by this claimed long-lasting extensional process. These observations raise the question whether the thrusts are older or younger than the continental extension. To address this question we have reprocessed and interpreted the deep seismic reflection profile CROP03/c that crosses the onshore hinterland sector, and investigated the structural setting of some of the Late Miocene-Pliocene hinterland basins (Cinigiano-Baccinello, Siena-Radicofani, Tafone, Albegna and Radicondoli basins) that are situated at the front or in-between the basement uplifts. The analysis of field structures and commercial seismic profiles has allowed the recognition that both substratum and basins' infill have been intensely shortened. These findings and the architecture of the basins suggest that the latter developed under a contractional regime, which would have started around 8.5 Ma with the onset of the continental sedimentation. This compressive stress state followed an earlier phase of continental extension that presumably started at ∼16 Ma (with the blocking of the Corsica-Sardinia rotation), and thinned both the continental crust and sedimentary cover producing most of the Serie Ridotta. The main phases of basin shortening are bracketed between 7.5 and 3.5 Ma, and thus overlap with the increase in the exhumation rate of the metamorphic cores at ∼6-4 Ma determined through thermochronological data. We therefore propose a correlation between the basin deformation and the activity of the nearby basement thrusts, which would have thus shortened a previously thinned continental crust. This chronology of deformation may suggest a geodynamic model in which the back-arc and hinterland sector of the Northern Apennines was recompressed during Late Miocene-Early Pliocene times. This evolution may be explained through different speculative scenarios involving a blockage of the subduction process, which may vary between end members of complete slab detachment and stalled subduction.

Other uses, including reproduction and distribution, or selling or licensing copies, or posting t... more Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited.

Geological map of the Potenza-Guardia Perticara area (Basilicata, Italy). Scale 1: 50,000

The geodynamic evolution of the Northern Apennines: insights from the Neogene-Quaternary basins

Tectono-sedimentary evolution of the post-nappe basins in the Northern Apennines

Analisi strutturale dei depositi pleistocenici dell'area di Firenze e di Rignano sull'Arno (Valdarno superiore), con considerazioni generali sulle deformazioni quaternarie dell'Appennino settentrionale

Geological map of the Lake Ziway-Asela region (Main Ethiopian Rift), scale 1: 50,000

We use new structural and apatite fission-track data together with apatite fission-track and (U-T... more We use new structural and apatite fission-track data together with apatite fission-track and (U-Th)/He data from literature to examine the tectonic evolution of the continental Upper Valdarno Basin, in the hinterland sector of the Northern Apennines fold-andthrust belt. This basin is located in-between two structural ridges, the Chianti Mountains to the southwest and the Pratomagno to the northeast. In our interpretation, the Upper Valdarno Basin developed at ca. 3.4-3.3 Ma as pop-down synformal-shaped depression bounded and controlled by oppositely-verging thrust-related structures, namely the thrust system lifting the Chianti Mountains and the southwest-facing backfolds at the base of the Pratomagno. This evolution is compatible with the accelerated exhumation rates at 4-5 Ma documented through apatite fission-track data along both the Pratomagno and Chianti ridges. Shortening suffered by basin deposits is clearly manifested by the outcrop-scale reverse faults and thrust-related folds affecting the Late Pliocene sediments (Castelnuovo dei Sabbioni Synthem), which are well exposed in the Santa Barbara mine. These strongly folded deposits are overlain unconformable by Early Pleistocene sediments (Montevarchi Synthem), which display evidence for syn-depositional normal faulting. This suggests that the Upper Valdarno Basin experienced a phase of normal faulting that started at the base of Pleistocene (ca. 2.6-2.5 Ma) and likely produced the large southwest-dipping "Trappola Fault", which affects the southwestern margin of the Pratomagno displacing the earlier backthrusts and backfolds. Basin evolution can be thus basically framed into a two-phase history, with extensional tectonics superposed onto compressional structures that were deactivated by ca. 2.7 Ma. Being the Chianti Mountains part of the 250 km-long regional line of thrusts and thrust-related folds (the so-called "Tuscan Nappe front"), the results of this study may also involve regional implications, as they would also hint for the tectonic history of other sectors and basins settled along-strike this regional element.

The intramessinian angular unconformity within the Radiconodoli syncline (Siena Tuscany Italy): structural and biostratigraphical preliminary data