Volcanoestratigrafía y evolución geológica de La Gomera

La isla de la Gomera (379 km2) esta situada en la parte occidental del archipiélago canario. Sus características geológicas son muy diferentes a las de las otras islas menores (La Palma y Hierro), pues es mucho más antigua y es la única en la que no existe actividad volcánica cuaternaria. La hace también especial el que para los modelos de génesis del archipiélago que suponen la existencia de una migración de la actividad volcánica de este a oeste, representa la excepción, pues se sitúa al oeste a pesar de ser casi tan antigua como otras islas más orientales

Naturaleza canaria: medio físico

Se propone cumplir con dos objetivos fundamentales: por un lado actualizar los conocimientos del profesorado que imparten materias con contenidos relacionados con la naturaleza Canaria y por otro, ofrecer una gama de actividades por niveles educativos y de carácter multidisciplinar. Todo ello para facilitar la aplicación de esta temática en los currículos de la Educación Secundaria y Bachillerato, que según el marco normativo, debe contemplarse. Se han estructurado los materiales en seis unidades didácticas según temas, que a su vez se organizan en dos grandes unidades: la primera trata el medio físico de Canarias y la segunda su flora y fauna, los principales ecosistemas terrestres y marinos así como las alternativas para su conservación.ES

A basic radial dike swarm of Boa Vista (Cape Verde Archipelago); its significance in the evolution of the island

A basic radial dike swarm unrelated to other basic units of Boa Vista (Cape Verde Archipelago) has been localized and characterized in the central sector of the island. According to new radiometric data three main stages in the evolution of Boa Vista are distinguished: the earlier (the Old Volcanic Complex: 17–16 Ma) is equivalent to the shield building stage of Hawaii and the later (the Recent Volcanics (8–4 Ma) is in some aspects comparable to the post-erosional stage. An important intermediate essentially felsic stage (the Trachytic–Phonolitic Complex: 14.3–12.8 Ma) followed the basaltic shield stage. This felsic stage has equivalents in some other oceanic islands as the Canary Islands, specially Gran Canaria, Tenerife, and La Gomera. The central sector of Boa Vista is also occupied by the Felsic Subvolcanic Complex, a unit consisting of phonolitic breccias, syenites and monzonites that represent the Trachytic–Phonolitic Complex hypabyssal roots. The felsic rocks as a whole constitute half of the total amount of igneous rocks on the island making up Boa Vista, the island with the highest percentage of felsic rocks in the Central Atlantic Ocean. More than 200 dikes of the basic radial swarm intruding the Felsic Subvolcanic Complex have been measured. The intensity of the multiple dike injection is sometimes rather high, roughly a dike every 5 m. The individual dikes have an observable mean length of about 300 m. The composition of these dikes is always foiditic (nephelinites, melilitites, and limburgites), slightly different in composition (more alkaline and richer in incompatible elements) to the other basic units of the island (the Old Volcanic Complex and the Recent Volcanics). The radial dikes converge in an area located NW of the geometrical center of Boa Vista, a zone where the hypothetical center of the Old Volcanic Complex and the Trachytic–Phonolitic Complex edifices must also have been situated. The ages obtained from the dikes (between 14.8 and 11.5 Ma) indicate that the radial injections are contemporary with the phonolites and the trachytes of the Trachytic–Phonolitic Complex and yet are part of the intermediate evolutionary stage of Boa Vista.Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

A new felsic cone-sheet swarm in the Central Atlantic Islands: The cone-sheet swarm of Boa Vista (Cape Verde)

The island of Boa Vista is one of the oceanic islands with the largest amount of felsic rocks reported in the world (50% of the total outcropping igneous rocks of Boa Vista). The felsic rocks are trachytes and phonolites generated within the second main stage of the volcanic activity that lasted about four million years. Three consecutive felsic episodes are distinguished: the first occurred between 14.5Ma and 13.5Ma, the second between 13.6 Ma and 12.0 Ma, and the third and last between 12.0 Ma and 10.4Ma. Their geochemical composition reveals the presence of crystal fractionation processeswith participation of feldspars andamphibole aswell as different accessory phases involved in each episode. The Boa Vista felsic cone-sheet swarm, the youngest third episode, is formed by several hundreds of peralkaline ne-phonolitic sheets distributedwithin a circular surface about 11 kmin radius. The cone-sheets conforma single general pattern characterized by a decreasing dip outward the structure, together with a constant dip of each individual sheet. The average inclination of sheets is around 40° in the sectors next to the centre of the structure whereas it is only about 30° next to its periphery. The magmatic focus of the sheets is located over 3 km deep almost coinciding with the convergence centre of a contemporary basic radial dike swarm

Structure, composition and age of the small islands of Santa Luzia, Branco and Raso (Cape Verde Archipelago)

The northern alignment of Cape Verde Archipelago contains three small islands in its central sector: Santa Luzia, Branco and Raso on which there is very scarce geological, petrological or geochronological information available. The three islands along with the island of São Vicente arise on a continuous underwater relief less than 50 m deep and about 70 km long that formed from separate volcanic edifices. The southernmost island, Raso is formed by accumulation of several tens of lava flows and some remaining strombolian cones. An erosion surface covered by sediments allows the separation of two different episodes of growth: the lower one older than 2 Ma, and the upper one between 0.9 and 1.2 Ma. The smaller island of Branco is the remnant of a large stratovolcano about 6 km in radius, 1000 m of altitude and between 5 and 6 Ma in age. Santa Luzia, the northernmost and largest island of this particular group is essentially a remaining rift zone between 4 and 7 Ma old, at least 600 m high, about 10 km long and 7 km wide. The SE extreme of the island is occupied by rocks of an older partially submarine stage of growth which, also include gabbroic intrusions crossed by a dense network of dikes whose age may be estimated in 8 Ma or more. On the contrary, the NW end shows the only remains of late post-erosion activity that is of much less volumetric importance and it has been dated between 0.8 and 1.4 Ma

Volcanoestratigrafía y evolución geológica de La Gomera

Disponible en las Biblioteca UCM. Sign. 55(460.41)ITI Ref. catálogo: http://cisne.sim.ucm.es/search~S29*spi?/tgeo-gu{u00ED}as/tgeo+guias/1%2C1%2C10%2CB/frameset&FF=tgeo+guias&8%2C%2C10/indexsort=-La isla de la Gomera (379 km2) esta situada en la parte occidental del archipiélago canario. Sus características geológicas son muy diferentes a las de las otras islas menores (La Palma y Hierro), pues es mucho más antigua y es la única en la que no existe actividad volcánica cuaternaria. La hace también especial el que para los modelos de génesis del archipiélago que suponen la existencia de una migración de la actividad volcánica de este a oeste, representa la excepción, pues se sitúa al oeste a pesar de ser casi tan antigua como otras islas más orientales.Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasFALSEpu

Constructive and destructive episodes in the building of a young Oceanic Island, La Palma, Canary Islands, and genesis of the Caldera de Taburiente

The results of new field observations, 23 new K-Ar determinations and sixteen previously published determinations provide the basis for the reconstruction of the subaerial volcanic history of the island of La Palma, after the seamount activity represented by the materials of the Basal Complex. An eruptive phase between 2.0 and 1.3 Ma formed a large shield. A period of volcanic quiescence followed, until around 1 Ma, during which a large lateral collapse partly destroyed the former edifice. Between 1.05 and 0.7 Ma, activity was renewed in the shield and a N-S ridge was built in the southern part of the island. Around 0.7 Ma, two new large lateral collapses affected the western part of both edifices, and they were followed by eruptions between 0.71 and 0.65 Ma which built a new edifice that partly filled the depressions thus created. The Caldera de Taburiente constitutes the eroded remnants of the depression formed in the northern shield. From 0.65 Ma to present, activity has been restricted to the N-S ridge, which has continued to grow southwards. There was a general N-S migration of volcanic activity with time, but in the shield the trend was northwest to southeast. Eruptive rates seem to have been fairly constant during the different eruptive phases considered, between 0.15 and 0.37 km3/ka. A very similar succession of constructive and destructive episodes has been obtained for the neighboring island of Hierro, but in this case the activity started around 0.8 Ma and eruptive rates were about 0.5 km3/ka

Cenozoic volcanism II: the Canary Islands

The authors thank C. Stillman, R. Tilling and A. Kerr for long hours dedicated to the careful revision of this chapter and for their very helpful comments.Book Description This book provides the first comprehensive account in English of the geology of mainland Spain and the Balearic and Canary Islands. It has been written by 159 research-active, mostly Spanish authors working together in teams from over 20 universities and other centres of research excellence. The 19 chapters begin with an overview of Spanish geology prepared by the editors, followed by a detailed examination of Iberian Precambrian and Palaeozoic rocks in Spain, Variscan magmatism and tectonics, and the Mesozoic and Cenozoic sedimentary and fossil record. Subsequent chapters deal with the Alpine orogeny in the Pyrenees, Betics and other mountain ranges of Spain and the Balearic Islands, and with Cenozoic magmatism, including the classic hot spot-related volcanism of the Canary Islands. The final chapter focuses on economic and environmental geology, emphasising metallic deposits and industrial minerals, hydrocarbon energy resources, water supply, and modern seismic hazard. Finally a bibliography of around 4000 references provide a uniquely valuable information source. Encompassing subjects as diverse as the origin of Spanish granites, the palaeogeographic and tectonometamorphic history of the Iberian plate, human evolution in the SW Mediterranean, and modern volcanism and earthquake activity, The Geology of Spain is a key reference work suitable not only for libraries across the world, but of interest to all researchers, teachers and students of SW European geology.Peer reviewe