Davide Scrocca

Slab Retreat and Active Shortening along the Central-Northern Apennines

The Quaternary geodynamic evolution and the tectonic processes active along the Central and Northern Apennines thrust fronts and in the adjacent Padane-Adriatic foredeep domains are analysed and discussed.

Time and space variability of “thin-skinned” and “thick-skinned” thrust tectonics in the Apennines (Italy)

In the Apennine fold and thrust belt of Italy, «thin-skinned» (i.e. detachment-dominated) and «thick-skinned» (i.e. crustal ramp-dominated) structures coexist, but with marked differences in both time and space. The external part of the northern Apennines and the deeper and younger portions (buried Apulian carbonates) of the thrust belt in the central and southern Apennines show limited amounts of shortening (in the range of 5–14 km). These result from similar deformation styles, involving the occurrence of relatively low-displacement, thick-skinned thrust ramps. The latter represent, at least in the northern Apennines, preexisting basement structures reactivated and inverted during contractional deformation. Interposed between the northern and southern parts of the fold and thrust belt, the central Apennines appear to constitute a transitional area in which strike-slip tectonics is relevant and carbonate platform units become predominant over pelagic basin ones, whereas the overall structure of the thrust belt becomes similar to that of the southern Apennines. In the latter, a peculiar structural style is revealed by the integrated analysis of surface and subsurface data. Structurally, the upper part of the thrust belt consists of allochthonous units made of Mesozoic peritidal carbonate platform and pelagic basin successions, and of Miocene foredeep sediments. These are completely detached from their original substratum and transported onto the 6–7 km thick, foreland carbonates of the Apulian platform. Based on available seismic data, the latter appears to be involved, together with the underlying Permo-Triassic clastics and, we infer, also the basement, in relatively low-displacement, thick-skinned structures. Therefore, in the southern Apennines, a transition from thin-to thick-skinned tectonics appears to have occurred through time. Thin-skinned structures characterise the shallower — and older — part of the thrust belt made of detached units, while a thick-skinned tectonic style is dominant in the buried Apulian carbonates of most recent accretion. The present boundary between the two different, superposed portions of the thrust belt consists of a low-angle, large-displacement thrust fault penetrated by numerous oil wells. Different styles and modes of contractional deformation in the investigated sectors of the Apennines appear to result from the geometrical requirement of maintaining strain compatibility and overall displacement continuity along a highly segmented orogen characterised by variable mechanical stratigraphy and southward increasing amounts of shortening.RiassuntoNella catena a pieghe e sovrascorrimenti dell’Appennino coesistono strutture che vedono coinvolto nella deformazione il basamento (tipo «thick-skin») e strutture scollate da questo (tipo «thin-skin»). La parte esterna dell’Appennino Settentrionale e le parti più profonde e più giovani (i carbonati della piattaforma Apula sepolta) dell’Appennino Centrale e Meridionale mostrano un raccorciamento limitato (compreso tra i 5 e i 14 km). Ciò deriva da stili deformativi simili, che producono rigetti relativamente bassi per la presenza di rampe di sovrascorrimento di tipo «thick-skin». Queste ultime rappresentano, almeno nell’Appennino Settentrionale, delle preesistenti strutture di basamento riattivate e invertite durante la deformazione contrazionale. Interposta tra le porzioni settentrionali e meridionali della catena, l’Appennino Centrale costituisce un’area di transizione in cui la tettonica trascorrente risulta di rilevante importanza e le unità carbonatiche di piattaforma divengono predominanti su quelle dei bacini pelagici, mentre la struttura generale della catena a pieghe e sovrascorrimenti diventa simile a quella dell’Appennino Meridionale. In quest’ultimo, lo stile strutturale tipico è rivelato dall’analisi integrata dei dati di superfice e di sottosuolo. Nella parte strutturalmente superiore di questo settore di catena sono presenti unità alloctone costituite da piattaforme a carbonati peritidali del Mesozoico e da successioni bacinali, sopra le quali sono presenti sedimenti miocenici di avanfossa e di bacini satelliti. Tale parte superiore è completamente scollata dal substrato di origine e trasportata sulla piattaforama carbonatica dell’avampaese apulo, che raggiunge potenze di circa 6–7 km. Sulla base dei profili sismici diponibili, la piattaforma apula appare coinvolta, insieme ai sottostanti sedimenti clastici permo-triassici e quindi anche al basamento, in strutture con basso rigetto di tipo «thick-skin». Di conseguenza, nell’Appennino Meridionale, un passaggio da un regime tettonico di tipo «thin-skin» ad uno di tipo «thick-skin» sembra essere avvenuto nel tempo. Le strutture «thin-skin» sono caratteristiche della parte più superficiale (e più vecchia) della catena costituita da unità scollate, mentre lo stile «thick-skin» è dominante nei carbonati apuli sepolti di più recente accrezione. Il limite attuale tra le due diverse, sovrapposte porzioni della catena è costituito da una importante superficie di sovrascorrimento a basso angolo, penetrata da numerosi pozzi petroliferi. Gli stili geometrici e le modalità di deformazione contrazionale differenziati nello spazio e nel tempo sembrano essere il risultato di esigenze di compatibilità geometrica della deformazione e di continuità dei rigetti lungo un orogene fortemente segmentato e caratterizzato da una stratigrafia variabile nelle sue caratteristiche meccaniche e da un aumento del raccorciamento verso Meridione.

Decollement depth versus accretionary prism dimension in the Apennines and the Barbados

(1) Along representative cross sections of the Apennines and the Northern Barbados accretionary prisms, we measured the area, the decollement depth, the angle a of the upper envelope and the angle b of the dip of the regional monocline. The continental sections of the Apennines accretionary prism have a deeper decollement than the oceanic sections of the Northern Barbados, 6-10 km depth and <1 km depth, respectively, because the sediment pile is thinner on the incoming Barbados plate and its denser oceanic structure is more easily subducted. Considering the frontal 50 km, the Apennines have an average cross- sectional area of 500 km 2 and the Northern Barbados Ridge of 100 km 2 . The total area is a function of the depth of the decollement plane. Therefore, at a given amount of subduction, the deeper the decollement depth is, the bigger the area of the wedge will result, assuming negligible compaction and erosion. As a consequence, the larger area/volume and higher elevation of the Apennines with respect to the Barbados is determined by the Apenninic deeper decollement. Despite these differences, the geometry of both decollements is, in some cases, comparable, in particular, close to the boundary between the crystalline crust and the sediment pile, where the main density and strength contrasts are concentrated. Variations in depth of the decollement occur moving along strike in both accretionary prisms. The geometry of the prisms is further controlled by the different values of a and b, their sum, and the distance of the accretionary prism relative to the subduction hinge. INDEX TERMS: 8099 Structural Geology: General or miscellaneous; 8150 Tectonophysics: Evolution of the Earth: Plate boundary—general (3040); 8122 Tectonophysics: Dynamics, gravity and tectonics; KEYWORDS: decollement depth, accretionary prism, Apennines, Barbados. Citation: Bigi, S., F. Lenci, C. Doglioni, J. C. Moore, E. Carminati, and D. Scrocca, Decollement depth versus

Thermal and tectonic evolution of the southern Alps (northern Italy) rifting: Coupled organic matter maturity analysis and thermokinematic modeling

The southern Alps were characterized by strong variations, both in space and time, of heat flow during Mesozoic rifting. The regional thermal history was reconstructed using organic matter (OM) maturity data from outcropping sediments. One-dimensional (1-D) thermal modeling performed on selected successions suggests that OM maturity was mainly controlled by high geothermal gradients (heat flow peaks of 85 to 105 mW/m2 in the Middle Jurassic) and differential burial during Norian–Early Jurassic extensional phases. The results of 1-D modeling show an eastward increase of heat flow peak values. These results were compared with those obtained with two-dimensional (2-D) thermokinematic models. The models show a time shift (ca. 10 Ma) in the heat-flow peak (Aalenian-Bajocian for 2-D and Bajocian for 1-D modeling). However, the Bajocian age was a priori imposed on 1-D models. Available geochemical data could be fitted assuming Aalenian-Bajocian peak ages. Consequently, this misfit is not alarming. The eastward increase in heat-flow peak values is tentatively explained with an eastward increase of radiogenic heat production in the crust instead of with differential stretching. The comparison of paleothermal data and numerical modeling was done to gain knowledge on the potentials and limitations of numerical modeling in frontier areas. Although some differences do exist in the results of geochemical and thermokinematic models, we can conclude that if a reasonable knowledge of the thermal parameters of both covers and basement is available, thermokinematic modeling can provide useful first-order estimates in frontier areas of heat flow and temperature evolution through time.

The tectonic puzzle of the Messina area (Southern Italy): Insights from new seismic reflection data

The Messina Strait, that separates peninsular Italy from Sicily, is one of the most seismically active areas of the Mediterranean. The structure and seismotectonic setting of the region are poorly understood, although the area is highly populated and important infrastructures are planned there. New seismic reflection data have identified a number of faults, as well as a crustal scale NE-trending anticline few km north of the strait. These features are interpreted as due to active right-lateral transpression along the north-eastern Sicilian offshore, coexisting with extensional and right-lateral transtensional tectonics in the southern Messina Strait. This complex tectonic network appears to be controlled by independent and overlapping tectonic settings, due to the presence of a diffuse transfer zone between the SE-ward retreating Calabria subduction zone relative to slab advance in the western Sicilian side.

Geochemical Barriers in \hbox {CO}_{2} Capture and Storage Feasibility Studies

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Transfer zones in an oblique back‐arc basin setting: Insights from the Latium‐Campania segmented margin (Tyrrhenian Sea)

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Subduction kinematics and dynamic constraints

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