Добірка наукової літератури з теми "Arc de Gibraltar"

AbstractThe Triassic–Jurassic rift-valley stage of Tethyan rifting in the Western-Central Mediterranean area is characterized by a development of a puzzle of plates and microplates with the deposition of continental redbeds (in the internal domains of the Gibraltar Arc and Calabria–Peloritani Arc) that can be considered a regional lithosome. This paper aims to reconstruct the chemical weathering conditions of the Triassic–Jurassic boundary in the Western-Central Mediterranean area using the geochemical and mineralogical composition of continental redbed mudrocks of Mesozoic age. The mudrocks from the Calabria–Peloritani Arc show higher values of weathering (mobility) indices (αMg=(Al/Mg)sed/(Al/Mg)UCC;αK=(Th/K)sed/(Th/K)UCC;αBa=(Th/Ba)sed/(Th/Ba)UCC) than the Gibraltar Arc samples. Furthermore, the CIA (Chemical Index of Alteration) and MIA (Mineralogical Index of Alteration) values and the ‘Rb-type indices’ (e.g. Rb/Sr and Rb/K ratios) are higher for the Calabria–Peloritani Arc mudrocks than the Gibraltar Arc samples. All these geochemical proxies closely resemble each other and show similar variations suggesting climatic changes towards humid conditions through the Uppermost Triassic to Lowermost Jurassic that favoured chemical weathering conditions. This period is probably characterized by seasonal climate alternations corresponding to an increase in palaeoclimatic humidity. The mineralogical compositions of the Mesozoic mudrocks further confirm these indications as shown by a higher abundance of kaolinite, related to warm–humid conditions, in the Calabria–Peloritani Arc mudrocks than in those of the Gibraltar Arc.

The pteridofloras of nine locations in the Gibraltar Arc were analyzed using a taxonomic distinctness index. We found that the index could be a proxy of historical biogeography of the pteridofloras from this area. Moreover, the value of the taxonomic distinctness index of the different locations showed relevant relationships with certain geographic variables. Finally, we hypothesize about the value of the information derived from taxonomic distinctness index for conservation of the pteridoflora in the Gibraltar Arc.

Abstract The Betics and Rif cordillera constitute the northern and southern segments of the Gibraltar arc. Two different fold-and-thrust belts, deriving from the South Iberian and Maghrebian paleomargins respectively, developed in front of this orogenic system. By contrast, the Flysch Trough units and the overlying Alboran crustal domain (internal zones), which are situated in the uppermost part of the orogenic wedge, are common to both branches of the arc. The Flyschs Trough units constitute an inactive accretionary prism, derived from a deep elongated trough. From three large-scale profiles and some lithostratigraphic features of the involved sedimentary sequences, the Betic and Rif external domains are compared, mainly from a structural point of view. Although they are generally considered to show major similarities, the Betic and Rif external domains are in fact strikingly different, mainly concerning the structural style, deformation timing and metamorphism: a) the thick-skinned structure in the External Rif domain vs thin-skinned in the Subbetic domain; b) the pre-Oligocene and Miocene stacking in the External Rif domain vs the exclusively Miocene one in the Subbetic domain, and c) the metamorphism present only in part of the External Rif domain (low-grade greenschists facies). By contrast, it was not possible to establish any difference in structural style and deformation timing between the Flysch units outcropping in both branches of the Gibraltar arc.

Detailed modelling of the present-day lithospheric structure is of paramount importance to understand the evolution of the Earth in the context of plate tectonics. The objectives of this thesis are twofold: the development of numerical methods to determine the lithospheric structure combining geopotential, lithostatic and heat transport equations, and the application of these methods to the study area, the Gibraltar Arc System region (GAS). The final product should be a useful 3D tool to analyse the lithosphere integrating, in a consistent manner, the thermal field, elevation, geoid and gravity anomalies, and SHF. In this sense, four main goals are:

1) Development of a numerical code to compute Bouguer anomalies from publicly available satellite-derived free air data in both continental and marine areas.

2) Development of a 1D method to calculate a first order lithospheric structure using elevation and geoid anomaly as input data.

3) Development of a 3D interactive code to perform lithospheric forward modelling, integrating SHF, gravity and geoid anomalies, and elevation.

4) Obtain a 3D image of the lithosphere geometry over the study region independent from seismic tomography in order to improve our knowledge of the deep, present day, lithospheric structure of the GAS region, and discuss the different geodynamic models proposed to explain its origin.

FA2BOUG is a FORTRAN 90 code to compute Bouguer anomaly specially intended to work with global elevation and free air data bases (Chapter 3). The program is designed to calculate in both continental and oceanic areas.

Chapter 4 deals with a method based on the combination of elevation and geoid anomaly data that allows for a rapid calculation of the crustal and lithospheric thickness over large regions under the assumption of local isostasy, thermal steady state, linear vertical density gradient for the crust, and temperature dependent mantle density.

Chapter 5 presents GEO3Dmod, a computer program intended to perform interactive 3D lithospheric forward modelling, integrating SHF, elevation, gravity anomaly and geoid anomaly. The program consists of two modules. The first one (GEO3Dmod) resolves the direct problem, i.e. given a lithospheric model (a set of layers with different properties), it calculates the 3D thermal and density structure of the lithosphere and the associated geophysical observables. The second one (GEO3Dmod_INTF) is a graphical interface designed to visualize and modify the lithospheric structure according to the differences between calculated and measured geophysical observables. To test the program, we used a number of synthetic models composed of crust, lithospheric mantle, sea water and asthenosphere.

In Chapter 6 we applied GEO3Dmod to the Gibraltar Arc System region using as initial geometry of the Moho and the LAB the 1D model obtained using elevation and geoid anomaly (Chapter 4). The application of the model to the GAS region yields a crustal and lithospheric structure that coincides fairly well with previous works. The whole Atlas Mountains seem to be affected by lithospheric thinning (60-90 km), but this feature is more conspicuous in its southern part, the Anti Atlas Variscan domain, and to the north, in the Middle Atlas. The eastern branch of the Atlas does not seem to be much affected by this lithospheric thinning. The strongest LAB topography gradients are present in the northern, southern and eastern limits of the thick lithosphere imaged beneath the Gulf of Cadiz, the Betics and the Rif (170-210 km). These regions coincide with the contact between the Iberian Variscan Massif and the Betic chain in the north, the contact between the Middle Atlas and the external Rif domain to the south, and the contact between the Betic-Rif orogen and the Alboran Basin to the east. The rough topography of the LAB suggests that the mantle contribution to the isostatic balance is not negligible, as confirmed by the isostatic residual anomaly map calculated for the GAS region. The presence of the SW-NE oriented zone of lithospheric thinning affecting the High, Anti and Middle Atlas and extending to the eastern Alboran Basin, as well as the parallel thick lithosphere zone extending along the western Betics, eastern Rif, Rharb Basin, and Gulf of Cadiz, put severe constraints on the proposed geodynamic models. Slab tear and asymmetric roll-back could be a plausible mechanism to explain the lithospheric thickening, whereas lateral asthenospheric flow would cause the lithosphere thinning. An alternative mechanism responsible for the lithospheric thinning could be the presence of a hot magmatic reservoir derived from a deep ancient plume centred in the Canary Island, and extending as far as Central Europe.

Située à l'extrême-ouest de la Méditerranée occidentale, la chaîne bético-rifaine s’est formée au travers d’une histoire orogénique alpine complexe, impliquant des processus de subduction liés à la convergence entre l’Afrique et l’Eurasie depuis le Crétacé. Une découverte importante de ces quatre dernières décennies d'investigations géologiques, a été la mise en évidence des vestiges d’un événement varisque dans les zones internes de la chaîne. Ces résultats soulignent bien la présence de deux systèmes orogéniques superposés, les zones internes de la chaîne bético-rifaine demeurent donc des zones privilégiées pour étudier l’importance de l’héritage structural et métamorphique dans les réactivations partielles ou totale par les évènements les plus récents. Ce travail est localisé dans le secteur de Beni Bousera, ou affleurent les roches crustales et mantéliques qui forment les unités les plus internes de la chaîne. Il s’appuie sur une étude menée à partir des analyses structurales et pétrologiques, des datations U-Th-Pb sur monazite et 40Ar-39Ar sur des micas et des amphiboles. Il nous permet de résumer l’histoire de la chaîne bético-rifaine de la manière suivante : 1) un événement de HP-HT affecte la base du domaine interne à ca 281 ± 3 Ma. Ces nouvelles données pétrologiques et géochronologiques obtenues dans le Rif interne sont corrélées avec les Bétiques, les Kabylies et le massif de l'Edough en Algérie, la ceinture mauritanienne et les Appalaches. Elles attestent d'un domaine convergent au cours du Carbonifère supérieur- Permien inférieur. Tous ces segments orogéniques font partie des Variscides nord-africains construits à la marge nord-ouest du Gondwana en réponse à une convergence entre cette dernière et la Laurentia. 2) autour de 29-26 Ma, un événement métamorphique avec un gradient de type Barrovien à Abukuma affecte les Sebtides (les unités les plus internes de la chaîne), et il est interprété comme résultant de l'évolution de la plaque supérieure d'une zone de subduction. Cet évènement alpin est caractérisé par un chemin prograde marqué par un réchauffement à la base des Sebtides entre 26 et 22 Ma. De telles conditions reflètent un amincissement et un réchauffement de la croûte liée à la remontée asthénosphérique due au retrait de la plaque plongeante ; cet événement marque le début d’un évènement extensif majeur. 3) Au Miocène inférieur à 22-20 Ma, les zones internes (ou domaine d’Alboran) sont affectées par une extension E-W contemporaine de l’ouverture du bassin d'Alboran dans un contexte arrière-arc, et par l’intrusion de filons granitiques dans les péridotites et les unités métamorphiques crustales du domaine interne. Cet évènement a permis l’exhumation finale des Sebtides. 4) Du Miocène inférieur au Miocène moyen, la chaîne bético-rifaine a acquis sa géométrie arquée (l’arc de Gibraltar) suite à la collision entre les zones internes et les zones externes, attestée par une phase de raccourcissement majeur de direction NE-SW à E-W, et 5) l’arc de Gibraltar est affecté par une phase de raccourcissement N-S ante-Pliocène de direction N-S, qui a modifié considérablement sa géométrie
Located at the extreme tip of the western Mediterranean, the Betic-Rif orogenic system is built through a complex alpine orogenic history involving processes of subduction related to convergence between Africa and Eurasia since the Cretaceous. A remarkable discovery during the last four decades of geological investigations, has been the remains of a variscan event in the internal zones of the belt. These results underline the presence of two superimposed orogenic systems, the internal zones of the belt thus remain a privileged area to study the importance of the structural and the metamorphic heritage in the partial or total reactivation by the most recent events. This work is located in the Beni Bousera sector, where crustal and mantle rocks that form the innermost units of the chain are exposed. Based on structural and petrological analyses, U-Th-Pb dating on monazite and 40Ar-39Ar dating on micas and amphiboles. The history of the Betic-Rif belt can be summarized as it follows: 1) a HP-HT event affects the base of the internal domain at around 281 ± 3 Ma. These new petrological and geochronological data obtained in the internal Rif, are correlated with the Betics, the Kabyle, the Edough massif of Algeria, the Mauritanian, and the Appalachian belts, attesting a convergent domain during the late Carboniferous – early Permian. All of these orogenic segments are part of the North African Variscides built at the north-western margin of Gondwana in response to convergence between the later and Laurentia. 2) at around 29-26 Ma, a Barrovian to Abukuma metamorphic event affects the Sebtides (the innermost units of the chain) and interpreted as the evolution of the upper plate of a subduction zone. This alpine event is typically characterized by a prograde metamorphic path marked by heating affecting the base of the Sebtides between 26 to 22 Ma, such conditions reflect thinning and heating of the crust related to the asthenosphere upwelling due to slab roll-back. This event marks the beginning of a major extensive event. 3) In the Miocene around 22-20 Ma, the internal zones are affected by an E-W extension contemporary to the opening of the Alboran Basin in a back-arc context, and the intrusion of granitic dykes into the peridotites and crustal metamorphic units, the exhumation of the Sebtides was complete at this time. 4) From early to middle Miocène, the Betic-Rif belt acquired its arcuate geometry (the Gibraltar Arc) during the collision between the Internal and the external zones, attested by de NE-SW to E-W shortening phases across the arc. 5) more lately prior to Pliocene, the Gibraltar arc was subjected to contractional possess related to a N-S shortening phase, which drastically altered its geometry

Au cours du XIe siècle avant notre ère la zone du détroit de Gibraltar assiste à l’arrivée sur ses côtes de populations phéniciennes venues du Proche-Orient. Ces peuples traversent en effet la mer Méditerranée pour venir s’installer et commercer avec les populations locales dans le but d’approvisionner la métropole de Tyr en métaux, pourpre et autres denrées susceptibles d’alimenter le commerce méditerranéen. C’est dans ce contexte, riche en contacts et en échanges, que se développe notre étude. Elle a pour objet les espaces sacrés qui jalonnent le parcours des pilotes, des voyageurs et des commerçants qui sillonnent le Détroit à bord de leurs navires. Les auteurs antiques, qu’ils soient poètes, géographes ou historiens, signalent un grand nombre d’autels, de temples ou même d’anecdotes mythologiques qui mettent en lumière un paysage sacré particulièrement riche dans cette zone de confins. Notre travail consiste à synthétiser toutes ces informations littéraires pour les mettre en parallèle avec les données obtenues par l’archéologie depuis la fin du siècle dernier. Au fil de l’analyse se révèle en filigrane l’existence d’un réseau d’espaces sacrés et de mythes qui viennent offrir un cadre religieux dans le Détroit. Cette synthèse inédite des données religieuses, recueillies sur les deux rives, permet une analyse et une première approche des phénomènes religieux maritimes dans la zone.Cette compilation des données religieuses doit nous permettre de mieux appréhender et de décrire avec plus d’acuité ce que devait être la vie religieuse des marins qui fréquentaient les colonnes d’Hercule. Il s’agit de déterminer les motivations qui justifient une présence si forte du religieux sur ces rivages : besoin de protection pendant la traversée, motifs économiques, contrôle des côtes et guide de la navigation… Il est également question de caractériser ces dévotions, de savoir par quels moyens et en quels types de lieux s’exprime la religion des marins. Il faut aussi s’interroger sur les émetteurs et les récepteurs de ce type de dévotions : les commerçants sont-ils les seuls à faire des offrandes ? Et quelles divinités sont mises en avant par la religion maritime de ces populations ?L’objectif de la démonstration est clairement de mettre en lumière et de mieux définir les différents éléments qui composent le paysage religieux maritime du détroit de Gibraltar. Le résultat est un essai de définition, de description et de mise en lien des divers éléments de ce réseau fait d’hommes, de divinités, de mythes, de lieux sacrés et de marques de dévotions, qui ont tous un point commun : la mer
This work deals with the localisation and functions of the Punic sacred places located at the strait of Gibraltar. The main purpose of this PHD is to discuss the links between those sacred spaces and navigation in this special part of the Mediterranean antique world. Using ancient writers’ quotes, talking about consecrated places on the shore of the south of Spain and the north of Morocco, we shall try and reveal a part of the sacred landscape that sailors and sea-sellers used to frequent. Many sites that have been excavated can be linked to a religious function (temple, sacred areas, holy caves or springs), we aim at discussing the evolution of those sites and the place they have in shore navigations and ports of trade
Este trabajo de tesis se centra en la localización y las funciones de los lugares sagrados púnicos del estrecho de Gibraltar. El objetivo principal de este proyecto es de describir los vínculos que existen entre estos espacios consagrados del litoral y la navegación en la zona del estrecho. Utilizando principalmente las referencias proporcionadas por los autores antiguos y los datos arqueológicos recuperados en las excavaciones de ambas orillas del estrecho (Andalucía, Algarve, Norte de Marruecos), intentamos describir, dibujar de la forma mas precisa posible el paisaje sagrado que los navegantes y comerciantes de esa época conocían. Varios de los sitios excavados tienen una función religiosa (templos, áreas sagradas, cuevas-santuario, fuentes consagradas), el objetivo del trabajo nuestro es presentar una síntesis de estos sitios, describiendo su evolución y el papel que ocupaban en las navegaciones costeras y en la red de puertos del estrecho

The Betic Cordillera of Spain and the Moroccan Rif constitute the northern and southern branches of the Gibraltar Arc, which is the western limit of the Alpine-Mediterranean system. The frontal units (i.e. the Guadalquivir Allochton of the Betic Cordillera and the Prerifaine Nappe of Morocco) have in the past been interpreted as olistostromes. Seismic data from the frontal part of the Gibraltar Arc suggest an accretionary complex migrating towards the west from the Western Mediterranean Basin. Seismic data in the Gulf of Cadiz, in the northwestern Atlantic margin of Morocco between Rabat and Tanger and in the Rharb Basin of northern Morocco have been interpreted and compared with field examples from the external Western Rif and the Guadalquivir region of the Betic Cordillera. The structure of the accretionary wedge consists mainly of imbricated thrusts and low-angle extensional detachments. The structures and internal deformation observed are similar to present-day accretionary wedges. Extensional and compressional structures are coeval with the foredeep development. The emplacement and collapse of the wedge were very rapid and occurred during Tortonian and Messinian time. The internal structure of the accretionary wedge is difficult to map since it originated from a deep-water passive margin succession with allochthonous Triassic evaporites and turbiditic wedges (flysch domain). The Prerifaine Nappe and the Guadalquivir Allochthon record several stages of accretion and westward motion of the Alboran domain, providing important constraints for the evolution of the Gibraltar Arc. Frontal accretion is coeval with uplift in the internal domain and back-arc extension in the Alboran region. A detailed sequence stratigraphic analysis of the Supra-Nappe succession has provided insights into the geodynamic evolution of the region and the effect of Pleistocene glacio-eustatic fluctuations.

Tese de doutoramento, Geologia (Geodinâmica Interna), Universidade de Lisboa, Faculdade de Ciências, 2012
The process of spontaneous subduction initiation at passive margins plays a central role in the plate tectonics theory, in particular in the Wilson Cycle paradigmatic concept, which states that oceans form, evolve and finally close. The Wilson Cycle requires that after a certain time of oceanic drifting passive margins are reactivated and subduction initiates. However, the process of transformation of passive continental margins into active continental margins with subduction zones is still far from understood, and spontaneous transition examples between these two types of margins are not known. In addition, recent works based on theoretical calculations and physical modeling showed that it is mechanically unfeasible to form a new subduction system in isolation from an already existing one, i.e. spontaneous subduction initiation. One way to solve this problem is to consider that subduction initiation may generally be induced by the proximity of another subduction zone or by stress transference from a nearby collision belt, i.e. induced subduction initiation. Therefore, passive margins in the proximity of pre-existing subduction zones would represent preferential sites for the formation of new subduction zones. In this work, the Gibraltar Arc and the Southwest Iberia Margin are used as case studies to investigate the role that the orogenic arcs may have in the formation of new subduction systems at passive margins. The Atlantic margins are generally described as the typical case of passive margins, often termed Atlantic type margins. However, there are at least two regions where the Atlantic oceanic lithosphere is being consumed in subduction zones: in the Scotia and in the Lesser Antilles arcs (in the Southwestern and central West Atlantic, respectively). These subduction zones seem to have been transferred from the Eastern Pacific ocean to the Atlantic domain and potentially represent precursors to a system of convergent zones that might ultimately result in the closure of the Atlantic Ocean. However, in these two systems the oceanic lithosphere has been subducted since at least the Early Cenozoic, without lateral propagation of the subduction zones along the adjacent Atlantic passive margins. The Gulf of Cadiz, i.e. the foreland of the Gibraltar orogenic arc, has been proposed as a potential locus for a subduction zone to propagate into the open Atlantic. On the other hand, the proximity of the Gibraltar collision belt to the Southwest Iberia Margin, together with the existing overall convergence between II Africa and Iberia, induces compressive stresses that, in association with the existence of more than 100 km long active thrusts (e.g. Horseshoe Fault and Gorringe Bank), make this margin a strong candidate for the nucleation of a new subduction zone. In order to better evaluate the post-Miocene tectonics and the main tectonic driving mechanism operating in the Gulf of Cadiz an up-to-date tectonic map of this area was produced. This map was based on the coupled analysis of a multi-survey MCS dataset and the recently compiled high resolution bathymetry dataset (the SWIM bathymetry). The mapping revealed the existence of three main systems of tectonic structures: i) the subduction-related Gulf of Cadiz Accretionary Wedge (CGAW); ii) a set of WNW-ESE striking dextral strike-slip faults (the SWIM fault system); and iii) a group of NE-SW striking northwest-directed thrusts located in the Southwest Iberia Margin (the NE-SW thrust system). The subduction-related accretionary wedge (GCAW) is materialized on the seafloor by a west dipping U-shaped surface and consists in an eastward thickening pile of westwards thrusted sediments. There are evidences that this thrust wedge is active and propagating westward. The SWIM fault system is a group of WNW-ESE striking subvertical strike-slip faults extending from the eastern part of the Gulf of Cadiz, i.e. the northwest Moroccan shelf, to the Horseshoe Abyssal Plain. These faults were interpreted in this work as the Present day dextral reactivation of the old Mesozoic Tethyan plate boundary. The NE-SW striking thrust system is a group northwest directed thrusts located along the Southwest Iberia Margin, comprising the Horseshoe fault, the Marquês de Pombal fault, the Tagus Abyssal Plain fault and the Gorringe northern thrust. This NESW thrust system seems to be the result of the migration of the deformation, in the Pliocene-Quaternary, from the realm of the Gibraltar wedge to the west (onto the Horseshoe fault region) and to the north along the West Portuguese Margin. These structures may be the expression of a new compressive deformation front. Besides these three tectonic systems, other important structures were also promptly recognized such as the ENE-WSW to E-W striking system of thrusts (e.g. the Portimão pop-up and the Coral Patch Ridge), related with the overall Cenozoic NubiaIII Iberia N-S convergence, and NE-SW striking Cadiz fault, a dextral strike-slip fault that probably accommodates part the westward movement of the Gibraltar Arc. The analysis of the multibeam bathymetry data from the northwestern part of the Gulf of Cadiz also revealed the existence of several intriguing kilometric crescentic depressions lying at depths between -4300 m and -4700 m, never before reported to occur at such great depths in the scientific literature. These features are located in the Horseshoe Valley between two major tectonic structures: the GCAW and the Horseshoe fault. Morphological parameterization of these features, coupled with detailed analysis of multi-channel and middle resolution seismic profiles, showed that these crescentshaped features were formed due to the existence of specific interaction between: a) regional active thrusts on top of which most crescentic depressions are carved; and b) tectonically induced scouring comprising localized erosion and simultaneous progradational sedimentation, produced by downslope turbiditic currents. The obtained results also suggest a possible contribution of fluid migration and extrusion processes, such as mud volcanism and associated pockmark formation, besides gravity driven landslides and slumping, in the development of the studied crescentic depressions. The active (mainly blind) thrusts in which the crescentic depressions are carved root in the GCAW décollement layer, to the west of the GCAW deformation front. Therefore, the crescentic depressions are interpreted as the morphological expression of the westward propagation of the deformation related with the GCAW, into the Horseshoe Valley domain. Besides the new produced cartography of the Gulf of Cadiz, the present work also benefited from the instrumental use of analog modeling experiments. Three main different modes of tectonic interference between the SWIM strike-slip fault system (related with the overall Nubia-Iberia convergence) and the GCAW (related with the Gibraltar subduction) were tested through analog sand-box modeling, namely: a) An active accretionary wedge on top of a pre-existent inactive basement fault; b) An active strike-slip fault cutting a previously formed, inactive, accretionary wedge; and c) Simultaneous activity of both the accretionary wedge and the strike-slip fault. The results obtained and the comparison with the natural deformation pattern favor a tectonic evolution comprising two main steps: i) the development of the Gulf of Cadiz Accretionary Wedge on top of inactive, Tethyan-related, basement faults (Middle Miocene to ~1.8 Ma); ii) subsequent reactivation of these basement faults with dextral IV strike-slip motion (~1.8 Ma to Present) simultaneously with continued tectonic accretion in the GCAW. These results exclude the possibility of ongoing active SWIM wrench system cross-cutting an inactive GCAW structure. The results also support a new interpretation of the SWIM wrench system as fundamentally resulting from strikeslip reactivation of an old (Tethyan-related) plate boundary. Detail mapping in the Horseshoe Abyssal Plain also revealed the existence of a new morphotectonic pattern near the intersection (corner zone) of the SWIM 1 fault and the Horseshoe fault. Based on combined analog and numerical experiments this pattern was interpreted as resulting from the (wrench-thrust) tectonic interference between two of the main tectonic systems recognized in the Gulf of Cadiz area: the SWIM faults and the NE-SW thrusts. Finally, the results presented in this work favor a hypothetic scenario in which the Gibraltar subduction is active, but decreasing in activity since the Miocene, at the same time that an incipient subduction zone may be nucleating in the Southwest Iberia Margin. The Gulf of Cadiz may be thus seen as a place where the proximity of a preexistent subduction system could be inducing the formation of a new subduction zone in the Atlantic.
O processo de iniciação espontânea de novas zonas de subducção ao longo de margens passivas tem um papel central na teoria da tectónica de placas, em particular no conceito paradigmático de Ciclo de Wilson, que afirma que os oceanos formam-se, evoluem e finalmente acabam por fechar. O Ciclo de Wilson requer que após um determinado tempo de evolução de um oceano as suas margens passivas sejam reactivadas e que uma nova zona de subducção se inicie. No entanto, o processo de transformação de margens continentais passivas em margens continentais activas com zonas de subducção é praticamente desconhecido, sendo que não se encontra documentado nenhum caso de transição espontânea entre estes dois tipos de margens. Acresce ainda que, trabalhos recentes de modelação numérica e cálculos teóricos mostraram que é fisicamente implausível a formação de novos sistemas de zonas de subducção isolados de zonas de subducção pré-existentes, isto é subducção espontânea. Uma forma de ultrapassar esta inconsistência é considerar que a iniciação de novas zonas de subducção é em geral induzida pela proximidade de outras zonas de subducção ou por compressão induzida a partir de um orógeno próximo, isto é, subducção induzida. Deste modo, as margens passivas próximas de zonas de subducção préexistentes podem ser vistas como os locais preferenciais para a formação de novas zonas de subducção. No presente trabalho, usa-se o Arco de Gibraltar e a Margem Sudoeste Ibérica como casos de estudo na tentativa de abordar a temática do papel que os arcos orogénicos podem ter na formação de novas zonas de subducção ao longo de margens passivas. As margens Atlânticas são geralmente descritas como o caso típico de margens passivas, pelo que estas são comummente denominadas de margens do tipo Atlântico. No entanto, há pelo menos dois locais na Terra onde litosfera oceânica Atlântica é consumida em zonas de subducção: no arco Scotia e no arco das Pequenas Antilhas (no Sudoeste Atlântico e no Atlântico Oeste central, respectivamente). Estes dois casos de zonas de subducção parecem ter sido transferidas do Oceano Pacífico oriental para o domínio Atlântico e podem ser vistos como os precursores do desenvolvimento de um novo limite de placas convergente que poderá em última instancia levar ao fecho do Oceano Atlântico. Porém, a litosfera oceânica tem vindo a ser subductada nestes dois VI sistemas desde pelo menos o Cenozóico inferior, sem ter ocorrido a propagação da subducção ao longo das margens passivas atlânticas adjacentes. O Golfo de Cádis, isto é, a bacia de ante-país do arco orogénico de Gibraltar, tem sido descrito como o terceiro local na Terra onde existe o potencial para uma zona de subducção pré-existente propagar-se para domínio Atlântico. Por outro lado, a proximidade do Arco de Gibraltar em relação à Margem Sudoeste Ibérica, em conjunto com a existência de convergência generalizada entre as placas tectónicas África e Ibéria, induz tensões compressivas nesta margem o que, em associação com a existência de cavalgamentos activos de largura superior a 100 km (por exemplo a Falha da Ferradura e o Banco Gorringe), a tornam numa forte candidata ao processo de nucleação de uma nova zona de subducção. Com o objectivo de melhorar a compreensão da tectónica pós-miocénica e dos principais mecanismos tectónicos forçadores a actuar no Golfo de Cádis foi elaborado um mapa tectónico actualizado à escala do golfo. Este mapa foi preparado com base na análise conjunta de dados de diversas campanhas de sísmica de reflexão multi-canal e de dados de batimetria multi-feixe de alta resolução recentemente compilados (batimetria SWIM). A cartografia mostrou a existência de três sistemas de estruturas tectónicas principais: i) o Prisma Acrecionário do Golfo de Cádis (PAGC); ii) um grupo de falhas de desligamento direito com a direcção WNW-ESE (sistema de falhas SWIM) e; iii) um grupo de cavalgamentos com a direcção NE-SW, vergentes para noroeste, localizados ao longo da Margem Sudoeste Ibérica (sistema de cavalgamentos NE-SW). O prisma acrecionário (PAGC) destaca-se no fundo do mar pela presença de um relevo morfológico positivo em forma de U que consiste na expressão superficial do empilhamento de sedimentos cavalgados para oeste. Este prisma gerou-se como resultado da existência da referida zona de subducção mergulhante para Este sob o Arco de Gibraltar. Existem evidências de que este prisma acrecionário ainda está activo e a propagar-se para oeste. O sistema de falhas SWIM constitui um grupo de falhas de desligamento direito, sub-verticais, que se estendem desde a área mais oriental do Golfo de Cádis, na plataforma continental do noroeste de Marrocos, até à Planície Abissal da Ferradura. Estas falhas foram interpretadas neste trabalho como tendo resultado da reactivação direita da fronteira de placas Mesozóica do Tétis. VII O sistema de cavalgamentos NE-SW é constituído por um grupo de cavalgamentos com direcção NE-SW, vergentes para noroeste localizados ao longo da Margem Sudoeste Ibérica que compreende a falha da Ferradura, a falha do Marquês de Pombal, a falha da Planície Abissal do Tejo e o cavalgamento norte do Gorringe. A deformação pliocénica-quaternária deste sistema é interpretada como a expressão da migração da deformação da frente de deformação do PAGC para oeste (até à zona da falha da Ferradura) e para norte ao longo da Margem Oeste Portuguesa. Estas estruturas parecem corresponder a uma nova frente de deformação compressiva, afastada do Arco de Gibraltar, que eventualmente poderá resultar na nucleação de uma nova zona de subducção na margem Sudoeste da Ibéria. Para além destes três sistemas tectónicos, foram reconhecidas outras estruturas importantes como é o caso dos cavalgamentos com direcção ENE-WSW a E-W (e.g. Banco de Portimão e Crista Coral Patch), relacionados com a convergência N-S generalizada entre as placas Núbia e Ibéria no Cenozóico, e a falha de Cádis que corresponde a um desligamento direito de direcção NE-SW e que acomoda parte do movimento para oeste do Arco de Gibraltar e da deformação limítrofe da margem sul portuguesa. Os dados de batimetria multi-feixe da área noroeste do Golfo de Cádis revelaram ainda a existência de um conjunto de intrigantes depressões em forma de crescente com dimensões quilométricas, localizadas entre os -4300 m e os -4700 m de profundidade. Objectos morfológicos com estas características nunca haviam sido identificados a tão grandes profundidades. Estas depressões estão localizadas no Vale da Ferradura entre duas estruturas tectónicas importantes: o PAGC e a falha da Ferradura. A análise morfológica destas formas, em conjunto com a análise detalhada de perfis de reflexão sísmica multi-canal e de média resolução, revelou que estas estruturas em crescente se formaram como resultado da interacção entre: a) actividade de falhas de cavalgamento que geram degraus tectónicos no topo dos quais os crescentes estão encaixados e b) erosão e re-deposição simultânea de sedimentos produzidos pela acção de correntes de fundo, provavelmente de origem turbidítica, que interagem com estes degraus tectónicos. Os resultados obtidos sugerem também uma contribuição de processos de migração e extrusão de fluidos, como vulcanismo de lama e formação de pockmarks, para além de movimentos de massa, no desenvolvimento das depressões em forma de crescente estudadas. Os cavalgamentos (essencialmente cegos) no topo dos quais os VIII crescentes estão encaixados enraízam ao nível do descolamento basal do PAGC, a oeste da sua frente de deformação morfológica. Deste modo, estas depressões em forma de crescente são também interpretadas como a expressão da migração da deformação relacionada com o PAGC para oeste, em direcção à área do Vale da Ferradura. Para além da nova cartografia tectónica do Golfo de Cádis, sustentada na interpretação de dados de sísmica multi-canal e batimetria multifeixe, este trabalho beneficiou ainda do uso instrumental de modelação análoga. Três modos de interferência tectónica entre o sistema de desligamentos SWIM (relacionado com a convergência generalizada entre a Núbia e a Ibéria) e o PAGC (relacionado com a zona de subducção do Arco de Gibraltar) foram testados através de modelação análoga, usando ”caixas de areia”, compreendendo: a) a formação de um prisma acrecionário sobre uma falha basal inactiva pré-existente; b) a actividade de uma falha de desligamento afectando um prisma acrecionário inactivo previamente formado; e c) a actividade simultânea de um prisma acrecionário e de uma falha de desligamento. Os resultados obtidos e a comparação com o padrão de deformação natural observado favorecem um cenário de evolução tectónica que compreende duas etapas principais: i) o desenvolvimento do PAGC sobre falhas basais inactivas, relacionadas com a abertura do Tétis (entre o Miocénico Médio e os 1,8 Ma); ii) subsequente reactivação destas falhas com movimento de desligamento direito (~1,8 Ma até ao presente) ao mesmo tempo que o PAGC se continuava a desenvolver. Os resultados excluem a possibilidade de existência de um sistema de desligamentos (SWIM) a cortar um prisma acrecionário inactivo (PAGC). Estes resultados suportam ainda uma nova interpretação do sistema SWIM, na qual estes desligamentos resultam fundamentalmente da reactivação direita da antiga fronteira de placas do extremo ocidental do oceano Tétis Alpino. A cartografia detalhada realizada na região da Planície Abissal da Ferradura permitiu também reconhecer um novo padrão morfo-tectónico existente na zona de intersecção (zona de canto) da falha SWIM 1 com a falha da Ferradura. Com base no uso conjunto de modelação análoga e numérica este padrão foi interpretado como tendo resultado da interferência tectónica (desligamento-cavalgamento) entre dois dos principais sistemas tectónicos activos no Golfo de Cádis: as falhas SWIM e os cavalgamentos NE-SW. IX Por último, os resultados apresentados neste trabalho favorecem um cenário tectónico hipotético no qual a actividade da zona de subducção presente sob o Arco de Gibraltar tem vindo a decrescer desde o Miocénico, ao mesmo tempo que uma zona de subducção incipiente poderá estar a desenvolver-se na Margem Sudoeste Ibérica. O Golfo de Cádis pode assim ser visto como um local onde a proximidade de uma zona de subducção pré-existente poderá estar a induzir a formação de uma nova zona de subducção no Atlântico.
Fundação para a Ciência e Tecnologia (FCT, SFRH/BD/31188/2006) e projetos: NEAREST (European Commission); ALMOND (FCT); TOPOEUROPE/0001/2007-TOPOMED (ESF/EUROMARGINS); SWITNAME (FCT); SWIMGLO (FCT); MVSEIS (ESF/EUROMARGINS); SWIM (ESF/EUROMARGINS).

This book presents the history of southern Iberia and the western Maghrib, and the Strait of Gibraltar between them, as a single bicontinental borderland, from roughly 1850 to 1970. Drawing on primary and secondary sources from several countries, it posits a long historical arc of transformation from a remote and hostile religious frontier into a multilaterally managed regional order. By the nineteenth century, the Strait of Gibraltar was becoming a dynamic focus of imperial positioning, migration, brigandage, and exchange. As a consequence, coastal outposts like Tangier, Gibraltar, and Melilla became centers of an emerging bicontinental society bringing together a kaleidoscope of ethno-religious groups. These developments produced conflict but also drew sovereign powers together to confront common challenges, such as controlling epidemic disease, defeating warlords, and managing borders. Thus, over the course of a century, despite periods of considerable violence, an international order gradually emerged in the western Mediterranean. As European empire withdrew in the late twentieth century, the region did not revert to the hostile frontier of earlier times but inherited the legacy of a relatively stable and resilient regional order. Conceptualizing the borderland in this way provides a single transnational framework to explore connections between Mediterranean geopolitics, colonialism, border formation, smuggling and brigandage, and the civil and international violence of the twentieth century. It also addresses the role of mobility in international relations, the dynamics of Muslim-Jewish relations in the context of European empire, and the ongoing controversies over Gibraltar, Ceuta, and Melilla.

This book traces the social history of the imperial garrison in the Colony of Natal in order to elucidate the reproduction, adaptation, and modification of Victorian British society on southern African soil. More specifically, it examines the divisions in colonial society and the influence of the garrison in shaping those divisions. The book considers a number of interrelated themes: class and gender, hierarchy and discipline, race and labor, pageantry and government, and the economic impact of garrisons and their costs. These themes are contextualized in relation to the distinctive role of Fort Napier as a garrison center. This chapter compares Fort Napier with other garrisons worldwide, including those in Gibraltar, Halifax, and Montreal; the jailer garrisons in Australia; and the garrison in New Zealand. It argues that Fort Napier and its garrison are unique because they influenced not only a settler society but also a major African society.

This volume brings together different varieties of English that have so far been treated separately: postcolonial and non-postcolonial Englishes. The different contributions examine these varieties of English against the backdrop of current World Englishes theorising, with a special focus on the Extra- and Intra-territorial Forces (EIF) Model (Buschfeld and Kautzsch 2017). Building on the general conception of Schneider’s (2003, 2007) Dynamic Model, the EIF Model aims at integrating postcolonial and non-postcolonial Englishes in a unified framework of World Englishes. The editors of the proposed volume claim that in the development of any kind of English around the world, forces from both outside and inside the community are in operation and lead to different outcomes as regards the status and characteristics of English. Each chapter tests the validity of this new model, analyses a different variety of English and assesses it in relation to current models of World Englishes. The case studies examine English(es) in England, Namibia, the United Arab Emirates, India, Singapore, the Philippines, South Korea, Japan, Australia, North America, The Bahamas, Trinidad, Tristan da Cunha, St. Helena, Bermuda, the Falkland Islands, Ireland, Gibraltar and Ghana.

This introduction addresses the book’s main arguments and themes and provides historical background on the history of the Strait of Gibraltar as a political boundary. It also outlines the book’s sources and methodology and lays out the chapter-by-chapter narrative arc. The Strait of Gibraltar first became a political border in the sixteenth century, with several smaller borders proliferating on its shores as multiple empires carved out coastal exclaves and spheres of influence. These borders form the crucial starting point for understanding the region’s political geography. Borders are the key sites of negotiation between sovereign power and human mobility. They possess material, legal, political, and metaphorical meaning, all of which are central to the ongoing process of mediating relationships among the empires, ethno-religious groups, and trade networks operating in the region.

The main statutory provisions in Gibraltar are: the Trustees Act 1895 as amended, which is based on early versions of trust legislation in England and the Trusts (Private International Law) Act 2015 which came into force on 17 September 2015. In addition, Gibraltar is a common law jurisdiction and English common law and the rules of equity are applied in accordance with section 2(1) of the English Law (Application) Act 1962.

An immense sand fort guards the entrance to the Cape Fear River and the fairway to Wilmington, the last major open port of the Confederacy, through which blockade runners supply vital materiel for Gen. Lee’s Army of Northern Virginia. On Christmas Eve 1864, a U.S. Navy armada unleashes the heaviest bombardment in history on the fort, in advance of landing 6,500 assault troops. But the U.S. commander, Maj. Gen. Benjamin F. Butler, falters, and only 2,300 troops make it ashore in roughening weather. They are stranded on the cold beach overnight without shelter. In the morning, the fleet sails away. Just three weeks later an even more powerful assault force returns, including USCT, who will play a crucial role in the battle. This assault is led by Brig. Gen. Alfred Terry and after six hours of heavy hand-to hand fighting forces the surrender of the fort.

This chapter compares the current legal and regulatory landscape of cryptocurrency regulations of selected countries. Countries have adopted distinct and disparate regulatory approaches in regulating cryptocurrency. Countries such as Gibraltar, Malta, Switzerland, Singapore, and certain states in the United States have enacted proactive, enabling, and industry-specific laws to regulate cryptocurrency. The Philippines and Denmark are relatively forward-looking in their endeavour to regulate cryptocurrency by allowing its utilization and/or trade but with a restrictive and cautious approach. Certain countries have imposed rigorous restrictions or banned the usage or trade of cryptocurrency. With the rapid evolution and emergence of cryptocurrency markets, policymakers are adopting different trajectories to develop a suitable regulatory framework to regulate cryptocurrency. Countries around the world should harness the capabilities of cryptocurrency by devising favourable regulations rather than inhibit the application of cryptocurrency.

The Mediterranean is a landlocked, semi-enclosed marginal sea that spans a maximum of 3,860 km in the west–east direction, and a maximum of ∼1, 600km in the north–south direction. Along its roughly 46,000 km of coastline, the basin is enclosed by mountainous terrain, except for a part of the North African margin to the east of Tunisia. The Mediterranean Sea contains very deep basins, more than 4 km, and has an average depth of approximately 1,500 m. Its only natural connection with the open (Atlantic) ocean is through the narrow Strait of Gibraltar, which contains a 284-m deep sill (at a width of ∼30 km), and reaches a minimum width of only 14 km (at a depth of 880 m) (Bryden and Kinder 1991). The Strait of Sicily subdivides the Mediterranean Sea into a western and an eastern basin. This strait is relatively wide (about 130 km) and contains a topographically complex sill-structure with an estimated average depth of 330 m (Wust 1961), reaching 365 and 430 m in the two major channels (Garzoli and Maillard 1979). The eastern Mediterranean contains two smaller marginal basins, namely the Adriatic Sea and the Aegean Sea. Watermasses are exchanged through both the Strait of Gibraltar and the Strait of Sicily by eastward surface and westward subsurface flows. This pattern of exchange results from a net buoyancy loss in the basins on the easterly side of the sills, primarily due to strong net evaporative loss from the Mediterranean, and secondarily to some net cooling. Deep water ventilation in the Mediterranean is primarily salt-driven, and secondarily temperature-driven. This is similar to the mode observed in the present-day Red Sea, but contrasts with the temperature-dominated mode in the modern world ocean. As such, the Mediterranean deep ventilation might be more appropriately described as halo-thermal rather than with the common term thermo-haline. This offers a useful analogue for world ocean circulation modes in past times with very warm and relatively equable global climates, such as the Mesozoic. Interestingly, the Mediterranean is characterized by periodic, widespread deposition of organic-rich sediments or ‘sapropels’ over periods of several thousands of years, similar (in miniature) to the deposition of ‘black shales’ in the Mesozoic oceans.

The introduction situates the importance of the book within current politics of nature in the Mediterranean. For the few last decades, there has been talk of a “war” on European migrant birds in the southernmost point of the European Union (EU) and former British colony—Malta. Located in the Mediterranean Sea, Malta has long been viewed as a bridge between Europe and North Africa, with its proximity to Tunisia and Libya in the south and Sicily to the north. Each spring and autumn, thousands of European migrating birds use the Maltese Islands as a resting place for their long journeys to and from their wintering grounds in Africa. While some people have claimed that the EU is another form of imperialism now imposed on the Maltese, what is missing from this understanding are the ways in which bird protection in Malta, the production of the Maltese “pothunter,” and environmental ideas of British migrant birds and semitropicality are rooted in part in Britain’s imperial past in the Mediterranean region. Moreover, Malta’s so-called unnatural relationship with birds has been put into sharp relief in comparison to Britain’s other previous Mediterranean colony—Gibraltar. Once a monument to empire, the British overseas territory is now promoted as a model of nature conservation and ornithological study in the Mediterranean.

While most naval action within the Mediterranean during the First World War took place in the east and in the Adriatic, in waters that lapped the shores of the disintegrating empires of the Ottomans and the Habsburgs, the entire Mediterranean became the setting for rivalry between 1918 and 1939. At the centre of the struggle for mastery of the Mediterranean lay the ambitions of Benito Mussolini, after he won control of Italy in 1922. His attitude to the Mediterranean wavered. At some moments he dreamed of an Italian empire that would stretch to ‘the Oceans’ and offer Italy ‘a place in the sun’; he attempted to make this dream real with the invasion of Abyssinia in 1935, which, apart from its sheer difficulty as a military campaign, was a political disaster because it lost him whatever consideration Britain and France had shown for him until then. At other times his focus was on the Mediterranean itself: Italy, he said, is ‘an island which juts into the Mediterranean’, and yet, the Fascist Grand Council ominously agreed, it was an imprisoned island: ‘the bars of this prison are Corsica, Tunisia, Malta and Cyprus. The guards of this prison are Gibraltar and Suez.’ Italian ambitions had been fed by the peace treaties at the end of the First World War. Not merely did Italy retain the Dodecanese, but the Austrians were pushed back in north-eastern Italy, and Italy acquired much of Italia irredenta, ‘unredeemed Italy’, in the form of Trieste, Istria and, along the Dalmatian coast, Zara (Zadar), which became famous for the excellent cherry brandy produced by the Luxardo family. Fiume (Rijeka) in Istria was seized by the rag-tag private army of the nationalist poet d’Annunzio in 1919, who declared it the seat of the ‘Italian Regency of Carnaro’; despite international opposition, by 1924 Fascist Italy had incorporated it into the fatherland. One strange manifestation, which reveals how important the past was to the Fascist dream, was the creation of institutes to promote the serious study (and italianità, ‘Italianness’) of Corsican, Maltese and Dalmatian history.

In the course of the seventeenth century the character of the relationship between the European states changed dramatically, with important repercussions in the Mediterranean. Until the end of the Thirty Years’ War in 1648, Catholic confronted Protestant, and confessional identity was an issue of surpassing significance for the competing powers in Europe. After 1648, a greater degree of political realism, or cynical calculation, began to intrude. Within a few years, it was possible for the English arch-Protestant Oliver Cromwell to cooperate with the Spanish king, while English suspicion of the Dutch led to conflict in the North Sea. The character of English involvement in the Mediterranean changed: royal fleets began to intervene and the English (after union with Scotland in 1707, the British) sought out permanent bases in the western Mediterranean: first Tangier, then Gibraltar, Minorca and, in 1800, Malta. The period from 1648 to the Napoleonic Wars was marked, therefore, by frequent about-turns as the English switched from Spanish to French alliances, and as the whole question of the Spanish royal succession divided Europe and opened up the prospect of spoils from a declining Spanish empire in the Mediterranean. While Spain’s difficulties were obvious, it was less clear that the Ottomans had passed their peak: the Ottoman siege of Vienna in 1683 was unsuccessful, but in the Mediterranean Turkish galleys still posed a serious threat, and their Barbary allies could be relied upon to give support when naval conflict broke out. Even so, the Venetians managed to gain control of the Morea or Peloponnese for several years, and, interestingly, it was they who were the aggressors. Bolder than they had been for some time, the Venetians ambitiously aimed to crack Turkish power in the regions closest to their navigation routes. In 1685 and 1686 they captured and demolished a number of Turkish fortresses on either side of the Morea, culminating in the capture of Nafplion on 30 August 1686. This was only the prelude to an attempt to clean up the Dalmatian coast, starting with the Turkish base at Herceg Novi, which they captured in September 1687.

Many remote communities rely on diesel generators as their primary power source, which is expensive and harmful to the environment. Renewable energy systems, based on photovoltaics and wind turbines, present a more sustainable and potentially cost-effective option for remote communities with abundant sun and wind. Designing and implementing community-owned and operated renewable power generation alternatives for critical infrastructure such as hospitals, water sanitation, and schools is one approach towards community autonomy and resiliency. However, configuring a cost-effective and reliable renewable power system is challenging due to the many design choices to be made, the large variations in the renewable power sources, and the location specific renewable power source availability. This paper presents an optimization-based approach to aid the configuration of a solar photovoltaic (PV), wind turbine generator and lead-acid battery storage hybrid power system. The approach, implemented in MATLAB, uses a detailed time-series system model to analyze system Loss of Load Probability (LOLP) and a lifetime system cost model to analyze system cost. These models are coupled to a genetic algorithm to perform a multi-objective optimization of system reliability and cost. The method was applied to two case studies to demonstrate the approach: a windy location (Gibraltar, UK), and a predominantly sunny location (Riyadh, Saudi Arabia). Hourly solar and wind resource data was extracted for these locations from the National Oceanic and Atmospheric Administration for five-year data sets. The village load requirements were statistically generated from a mean daily load for the community estimated based on the population and basic electricity needs. The case studies demonstrate that the mix and size of technologies is dependent on local climatic conditions. In addition, the results show the tradeoff between system reliability and cost, allowing designers to make important decisions for the remote communities.