Giorgio Minelli

The crustal structure of the northern apennines (Central Italy): An insight by the crop03 seismic line

In this paper, the CROP03-deep seismic reflection profile in the Northern Apennines is described and re-considered in light of new geophysical data and interpretations made available in the last five years (particularly from heat flow measurements, aeromagnetics, tomography, active stress determination and passive seismology). The crustal structure of the Northern Apennines is shown to be composed of two distinct domains. To the west is the Tyrrhenian domain and to the east is the Adriatic domain. These domains have distinctive geological and geophysical characteristics that exhibit distinct reflectivity patterns at all crustal levels. In the Tyrrhenian domain, the Upper Oligocene-Lower Miocene compressive structures are no longer recognizable, because they are dissected by subsequent extensional tectonic features. The seismic profile highlights the strong asymmetry of extensional deformation, and the upper crust is affected by a set of six major, east-dipping, low-angle normal faults. In the Adriatic domain, compressive tectonics have acted since the Middle-Miocene, and the pattern of shallow contractional structures is well preserved. The geological interpretation of the seismic data supports a thick-skinned style of deformation, where the basement is involved in the major thrust sheets. The good quality of seismic data also allows for determining the total shortening produced by the contractional structures. In the central part of the profile, at the border between the Tyrrhenian and Adriatic domains, seismic data shows the presence of an intermediate sector. The sector consists of a highly reflective window, where the refraction data indicate a local doubling of the crust for about 30 km. A scenario is presented that attempts to describe the geodynamics that drove the tectonic evolution of the Northern Apennines since the Upper Oligocene.

Anatomy of late orogenic extension: The Northern Apennines case

Abstract Late orogenic extensional structures overprint the compressional structures of the Northern Apennines fold and thrust belt. The Tyrrhenian Sea is the result of major continental extension and rifting which started in the thickened zone of the Apulian/ Corso-Sardinian collision. It is believed to have commenced as early as in the Late Oligocene or Early Miocene in the Corsica basin. Extension post-dates the collision by approximately 20 Ma. The extensional stress field observed in the internal part of the Northern Apennines co-exists with compression in the foreland part of the belt. Field, borehole and refraction and reflection data were used to investigate the geometry of extension and how it affected the compressional abric in the Northern Apennines. Analysis of the collected data has revealed a complex geometry for the extension across the belt. A geological cross-section from the island of Elba, to the west of the Italian Peninsula, to Ancona, in the east, as well as a geodynamic model for the evolution of the Northern Apennines is presented and discussed. From the Early Miocene stretching of the collision-thickened crust created a N-S rift which evolved into the present Northern Tyrrhenian Sea. Typically, two sets of extensional faults, a low-angle E-dipping and a W-dipping one are observed across the chain. Usually the W-dipping faults have similar attitudes to those of the older reverse faults, reactivating some of the thrusts as normal faults. The E-dipping normal faults, however, cut down-section through the pre-existing thrusts and, in the internal part of the belt, accommodate most of the displacement associated with extension. A change in fault polarity occurs in the Tuscan region and major faults dip towards the west. A-type subduction of the Apulian crust under the Corso-Sardinian block occurred after collision leading to the delamination of the Apulian lithospheric mantle away from the crust. Collision-induced delamination of the mantle lithosphere away from the zone of collision resulted in mechanical thinning of the lithosphere beneath the orogenic belt. This process induced late orogenic crustal stretching in the internal zone of the Northern Apennines. As the convergence between the Apulian and Corso-Sardinian blocks continued the extensional and compressional fronts, accompanied by the delamination, migrated from the hinterland towards the foreland of the orogen.

Outer Northern Apennines

The outer Northern Apennines (ONA) are an arc-shaped fold-and-thrust belt, with northeastward convexity and vergence, that plunges northwestward, extending through Romagna and Umbria—Marche to northern Latium. From the SW to the NE, it is situated between the inner Northern Apennines and the Po Plain—Adriatic foreland. To the S, the volcanic products of the Roman magmatic province cover it, while to the SE it is bounded by the Latium—Abruzzi carbonate platform. As for the Alps—ONA boundary the reader is referred to Castellarin (this vol., Ch. 13).

The Umbria-Marche arcuate fold belt (Italy)

Abstract In this paper the structural setting of the Umbria-Marche fold belt is briefly described. The basement-cover relationships and the primary or secondary origin of the arcuate shape are also discussed. Mainly on the basis of structural data, it is suggested that the Umbria-Marche fold belt can hardly be the result of a thin-skinned tectonics under little overburden, but one or more deep-seated detachment levels must have worked (thick-skinned tectonics) during the Mio-Pliocene transpressional phase. Furthermore, an orocline origin for the arcuate shape of the fold belt, resulting from a progressive history of oblique right-lateral shearing, is suggested. During the first deformative stage (stage 1a, Late Miocene) the cover, detached from the basement, is deformed by a NW-SE trending linear fold belt, whilst the basement is deformed by oblique right-lateral shear. Then (stage 1b), the linear fold belt is progressively bent, by right-lateral dragging in correspondence with the deep-seated shear zones. During the second deformative stage (stage 2, Early Piocene), the cover deforms in connection with the basement: the northern and the central sectors of Umbria-Marche Apennines undergo a prevailing shortening accomodated by NW-SE, NNW-SSE dip-slip thrusting; the southern sector undergoes a prevailing right-lateral shearing, accommodated by NNE-SSW oblique thrusting.

Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS): subsurface performances evaluation

According to the Mars Express mission, the MARSIS primary scientific objectives are to map the distribution of water, both liquid and solid, in the upper pot-lions of the crust of Mars. Three secondary objectives are also defined subsurface geologic probing, surface characterization, and ionosphere sounding. In order to obtain the primary objectives the Radar Sounder design was based on the Ice/water interface and Dry/ice interface scenario: defining the material composition of the first layers and porosity and the pore filling materials. Concerning the surface, we have characterized the geometric structure in terms of a large-scale morphology, on which a small-scale geometric structure, due to rocks, is superimposed, taking into account also that recently the structure of the planets surface was described by means of fractals and in particular the new MARS surface models obtained by processing of the MOLA data. According to these models, this paper provides a description of the operational planning approach and expected performances of MARSIS.

Mesostructural analysis of S-C fabrics in a shallow shear zone of the Umbria–Marche Apennines (Central Italy)

Abstract Several examples of foliated fault zones characterized by penetrative S-C fabric are exposed in the Umbria–Marche region, often associated with major thrusts. These tectonites, dominated by pressure-solution processes, are developed at shallow depths (<3 km) in sedimentary rocks. In this paper, we perform a detailed structural analysis of the Scheggia Thrust Zone (STZ), a significant example of S-C tectonite spectacularly exposed in the Umbria–Marche Apennines. We reconstruct both the architecture and internal structure of the shear zone, focusing on the factors controlling the genesis and development of the tectonic pattern such as: (a) anisotropy; (b) lithological contrast; and (c) distance from the fault core. The STZ shows an intensely cleaved fault core (S-C fabric) and a thick and asymmetric damage zone developed in the footwall rocks. By analysing the spacing of the S-surfaces, we observe that the magnitude of deformation decreases with distance from the fault core. However, far from the fault core the magnitude of deformation is strongly controlled by the lithology of the protolith: almost undeformed calcareous beds alternate with intensely sheared intervals, localized along weak, marly horizons, also characterized by flattened S-planes. Based on these data we have divided the STZ into three subzones where the deformation is mainly driven by: (1) distance from the fault core; and (2) the lithology of the protolith. Marly horizons into these subzones, with respect to the calcareous horizon, show that: (i) S-planes are more closely spaced; and (ii) the angle between C- and S-planes is smaller. Our study confirms that the rhythmic alternation of calcareous and marly rocks can favour the development of foliated fault zones, also producing an increase in pressure-solution cleavage at shallow crustal conditions.

Joint Distribution in a Fractured Carbonate Reservoir in the Umbria-Marche Anticlines (Central Italy)

A detailed structural analysis of the discontinuities of the Calcare Massiccio Fm. (Early Liassic) of the Umbria-Marche fold and thrust belt (central Italy) was carried out in order to define the fracture pattern typical of a massive limestones from a carbonate shelf at the core of an anticline structure, This research was made with the aim to apply the results to the modelling of the Cavone oil field fractured reservoir (Po Valley subsurface, northern Italy). The attitudes of rock discontinuities, including bedding, faults and joints were surveyed and their temporal and spatial relationships recorded.

Identifying Wrinkle Ridges from Mars MGS and Viking Mission Data: Using GRASS GIS in Planetary Geology

During the past few decades, numerous missions to Mars have sent information about the red planet. The missions have shown that Mars has ice on its poles and that ice could be present all over the planet subsurface. The presence of ice on the subsurface could drive particular geological structures called ‘wrinkle ridges’. In this work, Viking image data and the latest Mars Global Suveyor (MGS) data have been imported and stored in a common geospatial database using GRASS GIS as a tool for planetary geology. This study has focused on a subregion of Solis Planum where wrinkle ridges have been localised and both Viking images and MGS altimetry and imagery data are available. Raster data at different resolutions and with different projection parameters have been imported into GRASS GIS and projected in a common reference system. Raw, unprojected data have been processed and rectified using the GRASS image modules. Imagery data have been used to detect planimetric features, whereas basic morphometrical analysis has been performed from the gridded elevation data coming from MGS Mars Orbiter Laser Altimeter. Address for correspondence: Alessandro Frigeri, Dipartimento di Scienze della Terra, Università degli Studi di Perugia, Pzza Università 1, 06100 Perugia, Italy. E-mail: afrigeri@unipg.it 256 A Frigeri, C Federico, C Pauselli and G Minelli