Search

This essay shows some new dating of the Basal Complex of La Gomera Island and among them, the first ones obtained using the 40Ar-39Ar methodology. Two of them are rocks of the Submarine Edifice. In the first one we obtain an age of 11,49 ± 0,66 Ma by the 40Ar-39Ar method, and in the second one 11,4 ± 1,6 Ma by the K-Ar method. These ages reveal that the volcanic activity of the NW outcroping Submarine Edifice is approximately 11,5 Ma in age, close to the beginning of the Lower Old Edifice activity. The third sample dated also by the 40Ar-39Ar method, is from the only syenitic rocks outcrop of La Gomera (Tamargada syenite); its age, 7,59 ± 0,81 Ma, confirms that these rocks represent the roots of one of the Old Edifice felsic episodes and that they do not belong to a felsic stage contemporary with the submarine growth of the island.

A more than 1000m thick pile of basaltic lava flows and pyroclasts dipping seawards rises on the western sector of San Vicente. Several systems of dikes cut across the succession that is composed of two different sequences. The lower sequence (Lazareto Formation), about 400 m thick, is formed mainly by pahoe-hoe, frequently ankaramitic, basalt lavas and some breccias intercalated. This sequence is exposed in small hills and low rounded ridges of gentle slopes. The upper sequence (Monte Cara Formation), some 700 m thick, consisting in individually thicker basaltic lava flows with typical scoria levels is well exposed in high scarps. Numerous subvertical dikes cross the entire succession. The dikes vary increasingly their strike from south to north. Frequent sills (one every 3-5 m) also intrude the lower sequence. The distribution of the lava flow dip strikes as well as the dike strikes suggests that the succession as a whole was part of a central volcanic edifice, of which the eruptive centre was once located south of the city of Mindelo. This giant volcanic edifice, 16-20 km in diameter and 1600-2000m high, would have extended off the present coast. According to the radiometric ages obtained the volcano built up between 6,1Ma and 4,6 Ma with maximum activity concentrated between 5,5 and 5 Ma.

The new radiometric data from felsic domes on La Gomera allow to separate two different felsic both intrusive and extrusive episodes on the island. The early one, upper Miocene in age, includes the domes on the eastern sector of the island as well as the radial and the conical dikes cropping out on the north. Within this early episode of felsic magmatism, the domes on the eastern sector and the so called eastern radial dike-swarm seem to be contemporaneous and slightly older (8.6-7.9 Ma) than the western radialdike swarm and the con e-sheet complex, a structure which also includes some related domes (7.5-6.4 Ma). A later felsic episode, lower Pliocene in age (4.5-3.9 Ma),includes all the rest of existent domes on La Gomera which are less alkaline and peralkaline than the older ones.

The Jandia is one of the three main edifices identified in the Old Basaltic Series of Fuerteventura. It shows now a semicircular shape with a nortwards facing opening. This large volcano built up by lava flows and pyroclastics corresponding to three successive subseries: Lower, Medium and Upper Series all separated by unconformities. The jandia Lower Series is probably equivalent to the Lower Series which has been identified in the Central Edifice farther to the north-east. A fourth period of activity (Late Series) which formed a low table land, took place west of the present semicircular edifice.

Se sitúa el vulcanismo calcoalcalino de Atienza en un marco estructural a diferentes escalas. Sus características lo hacen compatible con un modelo de reactivación continental, consecuencia de una colisión continente-continente> en el cual son factibles diferentes hipótesis petrogenéticas. Se destaca la relación de este vulcanismo con el ciclo hercínico, con las fosas molásicas pérmicas y con la tectónica de fracturación tardihercínica. Por otra parte, se separa netamente del vulcanismo posterior, de edad mesozoica, de la Cordillera Ibérica, cuya génesis ha de estar ligada, por el contrario> a la evolución de una estructura de tipo aulacogénico.st