Anticlockwise pressure–temperature paths record Variscan upper‐plate exhumation: Example from micaschists of the Porto Vecchio region,Corsica

To better understand the evolution of deep‐seated crust of the Variscan orogen in the Sardinia‐Corsica region, we studied garnet‐bearing micaschists which were sampled 3 km east and 15 km northeast of Porto Vecchio, south‐eastern Corsica. After a careful investigation of the textural relations and compositions of minerals, especially of zoned garnet, a P–T path was reconstructed using contoured P–T pseudosections. U–Th–Pb dating of monazite in the micaschists was undertaken with the electron microprobe. The micaschists from both localities were formed along similar anticlockwise P–T paths. The prograde branch of these paths starts at 3 kbar close to 600°C in the P–T field of sillimanite and reaches peak conditions at 7 kbar and 600 (15 km NE of Porto Vecchio) to 630°C (3 km E of Porto Vecchio). The metamorphism at peak P–T conditions happened c. 340 Ma based on low‐Y (<0.65 wt% Y₂O₃) monazite. Ages of monazite with high‐Y contents (>2 wt% Y₂O₃), which probably have formed before garnet, scatter around 362 Ma. The retrograde branch of the P–T paths passes through 4 kbar at ~550°C. We conclude that the micaschists belong to a common metasedimentary sequence, which extends over the Porto Vecchio region and is separated from other metamorphic rock sequences in the north and the south by major tectonic boundaries. This sequence had experienced peak pressures which are lower than those determined for metamorphic rocks, such as micaschist and gneiss, from north‐eastern Sardinia. At present, we favour a continent–continent collisional scenario with the studied metasedimentary sequence buried during the collisional event as part of the upper plate. The contemporaneous high‐P metamorphic rocks from NE Sardinia were part of the upper portion of the lower plate. The addressed rocks from both plates were exhumed in an exhumation channel.     

Latitudinal variation of wind erosion of crater ejecta deposits on Mars

Wind erosion seems to be the dominant process eroding crater ejecta deposits and sorrounding materials on Mars. In the equatorial zone, ejecta deposits are eroded back by scarp recession, where scarp heights appear to be approximately equivalent to ejecta thickness. In mantled areas, escarpments develop by relatively rapid deflation of sorrounding aeolian debris, leaving the ejecta deposit (continuous deposit and zone of high density of secondary craters) standing high above sorrounding terrain. If the rate of scarp recession is controlled by the rate of aeolian undercutting of escarpment bases, then recession rates may scale roughly as the inverse with respect to scarp height. Thus, preferential preservation of ejecta deposits emplaced in thickest aeolian debris may occur. An empirical model developed for wind erosion of ejecta deposits in nonmantled areas suggests that removal of ejecta materials on the average is exceedingly slow (～10^?5m/yr for 10m high scarp). On the other hand, rapid deflation of aeolian debris around crater ejecta is implied. Results suggest high differential aeolian erosion rates that are a function of both grain sizes and large-scale surface roughness. Aeolian activity on Mars has probably been dominated by rapid recycling of fine-grained debris, the bulk of which formed under more erosive conditions prevalent in the early history of Mars.     

PIANCALDOLI METEORITE: CHEMISTRY,MINERALOGY AND PETROLOGY

The fall occurred near Piancaldoli, Florence, Italy, at 19.14 U.T. on the 10th August 1968. The fireball broke up in the atmosphere producing a cloud like a balloon. The trajectory and the terminal point were calculated, leading to the recovery of three small meteoritic fragments, found on the roof of a house. Chemical analysis gave the following results: SiO₂ 40.80; TiO₂ 0.15; Al₂O₃ 2. 70; Cr₂O₃ 0.47; FeO 17.20; MnO 0.07; MgO 25.18; CaO 1.95; Na₂O 0.64; K₂O 0.07; P₂O₅ 0.20; NiS 0.93; FeS 6.24; Fe° 2.40; Ni° 0.40; Co 0.05; sum 99.45. In the lithic portion of the meteorite the following minerals were found: both clino and orthopyroxenes (En = 76 to 98%), olivines (Fo = 66 to 98%), troilite, pyrrhotite, pentlandite, kamacite, ilmenite, apatite, merillite, schreibersite, chromite and Henderson phase. From all the mineralogical and petrological data, we conclude that the Piancaldoli meteorite is an “unequilibrated ordinary chondrite,” LL3. The microbrecciated structure of the rock and some shock features were observed, while the rock as a whole is unshocked, suggesting that these features were caused by impact events which took place during the accretion of the parent body.     

A contribution to the implementation of ICZM in the Mediterranean developing countries

The purpose of this paper is to assess the level of implementation of Integrated Coastal Zone Management (ICZM) principles in the Mediterranean developing countries at the moment of signing the protocol on ICZM for the Mediterranean, in the framework of the UNEP Mediterranean Action Plan of the Barcelona Convention. This assessment is based on the results of two advanced seminars on ICZM promoted by the Azahar programme of the Spanish Agency for International Cooperation for the Development (Ministry of Foreign Affairs and International Cooperation). The contribution of the participants of the seminar, who are representatives of national agencies related with ICZM in different Mediterranean countries, have been collected through a questionnaire including: (i) a ranking of the main coastal sectors and the main coastal issues of each country; (ii) significant initiatives for the sustainable development of the Mediterranean coastal zones; and (iii) the evaluation of the ICZM progress. The state of the coast, the level of implementation of ICZM and the main problems faced to apply it, have been detected for each country. None of the consulted countries have a full implemented integrated coastal zone management, the major problems being: (i) the lack of financial commitment for the implementation of ICZM; (ii) the lack of an assessment and monitoring system; (iii) the lack of knowledge regarding the coastal system; (iv) the lack of qualified human resources; and (v) the lack of public participation and administrative integration strategies based on information. From these conclusions, some recommendations to improve ICZM are also provided. The work presented in this paper is the starting point to assess the evolution and the reference from which ICZM will be improved through the protocol on ICZM for the Mediterranean.     

Three-dimensional experiments on landslide generated waves at a sloping coast

This paper describes new three dimensional experiments on water waves generated by landslides. The landslide is reproduced by a rigid elliptical body, sliding along an inclined plane (slope of 1/3, 1 vertical, 3 horizontal). The generated water waves are free to propagate both offshore and alongshore, since the plan dimensions of the used wave tank are of at least one order of magnitude larger than the width of the landslide, which can be considered to be a scale of the wave length. The experimental study has been carried out reproducing both subaerial and partially submerged landslides. The wave generation process is studied by means of video records of the near field flow and measurement of the landslide movement; the properties of the waves propagating along the coast are described on the basis of runup gauges. The waves observed during the experiments always present first a crest and then a trough; as the first wave propagates away from the generation area the crest tends to become smaller than the trough and the maximum runup along the coast is given by the second or by the third wave. An important feature is that the observed runup along the coast firstly grows with the distance from the generation area, it reaches a maximum value at about two times the width of the landslide, and then decreases. An estimate of the celerity at which the waves propagate along the coast is given on the basis of gauge measurements; it results that the crests propagate faster than the troughs, and the wave period increases.     

New gravity maps of the Eastern Alps and significance for the crustal structures

The deep seismic profile Transalp crosses, from north to south, Germany, Austria and Italy. The gravity measurements for each country were made by national agencies with different reference systems and data reduction methods. Within the frame of the Transalp-project a comprehensive database of the Eastern Alps was compiled covering an area of 3.5° by 4° in longitude and latitude (275 by 445 km), respectively. To increase the data coverage in the south Alpine area two gravity surveys were carried out, resulting in 469 areally distributed new stations, of which 215 have been measured with the intent to improve the geoid in the area of the planned Brenner Basistunnel (BBT). The resulting gravity database is the best in terms of resolution and data quality presently available for the Eastern Alps. Here the free air, Bouguer and isostatic gravity fields are critically discussed. The spatial density of existing gravity stations in the three countries is discussed. On the Italian side of the Alps the spatial density is rather sparse compared to the Austrian side. The Bouguer-gravity field varies between − 190 * 10^− 5 m/s² and + 25 * 10^− 5 m/s², with the minimum located along the Alpine high topographic chain, but with a small offset (a few tens of km) to the greatest topographic elevation, showing that the Airy-type local isostatic equilibrium does not fully apply here. The maximum of the Bouguer anomaly has an elongated shape of 100 by 50 km located between the towns of Verona and Vicenza and covers the Venetian Tertiary Volcanic Province (VTVP), a feature not directly related to the plate collision in the Eastern Alps. The gravity high is only partly explainable by high-density magmatic rocks and requires also a deeper source, like a shallowing of the Moho. The isostatic residual anomalies (Airy model) are in the range ± 50 * 10^− 5 m/s², with the greatest positive anomaly corresponding to the location of the VTVP, indicating here under-compensation of masses. At last a discussion of a 2D density model based on reflection seismic data and receiver functions is made.     

Resilience and seismic risk perception at school: a geoethical experiment in Aiello Calabro,southern Italy

The last few years have seen the debate on the geoethics of environmental and climatic protection growing to include resilience as a central idea within this new discipline, which holds many similarities with geography. Resilience analysis often looks at the capacity to re-establish conditions of equilibrium within a system which has been hit by a serious shock, e.g. a natural or man-made disaster. Geoethics works, in tandem with geological analyses and the geography of risk, to inform a population and develop integrated risk management in such a way as to strengthen a community’s resilience. The aim of this work is to study some people’s capacity to overcome what was potentially a disastrous event and, through a process of reconstruction, turn it into an occasion for growth. The experiment, carried out in the primary and middle schools in Aiello Calabro (Calabria, southern Italy), was conducted on the basis of the belief that there is a close relationship between a population’s having a realistic understanding of the risk of such an event, e.g. an earthquake, and high levels of resilience. We also tried to gain an insight into the relationship that may exist between resilience in primary and secondary school children and methods of coping which give an appropriate management of seismic risk. To be more precise, we try to discover whether there is a link between good/appropriate resilience and good/appropriate risk management.     

The entropy of a cratered surface

The definition of the entropy of a cratered surface is given by analogy with the entropy of the information theory. The saturation, defined as the ratio between the area covered by craters of diameterD and the total observed area, is adopted as a measure of the probability to find a portion of a planetary surface covered by craters of the given diameterD.The meaning of such a new function is discussed in comparison with statistical approaches to the study of the cratering. Applications to Mercury are discussed.Paper presented at the European Workshop on Planetary Sciences, organised by the Laboratorio di Astrofisica Spaziale di Frascati, and held between April 23–27, 1979, at the Accademia Nazionale del Lincei in Rome, Italy.     

Antigorite polysomatism: behaviour during progressive metamorphism

Antigorite forms a polysomatic series of discrete compositions that are chemographically colinear with chrysotile/lizardite, Mg₃Si₂O₅(OH)₄ and talc, Mg₃Si₄O₁₀(OH)₂. The compositional variations of antigorite correspond to discrete changes in the lattice parameter, a. A complete suite of antigorites, collected from a cross-section representing increasing metamorphic grade through the Swiss and Italian Alps, has been studied by optical and transmission electron microscopy (TEM). The specimens within this suite range from those formed near the lower stability limit of antigorite (250 °C) through to those formed near its breakdown temperature (550 °C). The lower grade samples belong to the regionally metamorphosed upper Pennine Ophiolites of the Oberhalbstein-Malenco area, while higher grade antigorites were obtained from regionally metamorphosed Malenco serpentinites. The highest grade samples are also from Malenco. They underwent a later contact metamorphism within the thermal aureole of the Bregaglia Intrusive. The lattice parameter a of antigorites evolves from longer (60 Å) to shorter (35 Å) values with increasing metamorphic grade. However, individual antigorites almost invariably show a heterogeneous distribution of a periodicities with higher values close to grain boundaries or reaction fronts and lower values towards the grain centers. The crystal-chemical evolution of antigorite, expressed by reduction in a, is usually accompanied by increased crystallinity. With the TEM, this is seen as an increase in crystallite size and a decrease in the number of crystal defects (twinning, polysomatic disorder, modulation dislocations, wobbling, offset). The structural and compositional evolution of antigorite requires intracrystalline diffusion and reconstructive transformations at relatively low temperatures. Therefore, the process of evolution is sluggish. Equilibrium is frequently not attained, and relics of longer a periodicities can be observed. In addition, relics of chrysotile may be observed in high-grade metamorphic rocks of the Malenco area, in which antigorite coexists with new-formed olivine. Only at one locality is there evidence of equilibrium: antigorite formed at 435 °C has a=43 Å; it shows very little variation in the a periodicity, and it is characterized by a homogeneous annealing texture. A geothermometer based upon a periodicities, as proposed by Kunze (1961) has limited practical applicability.