STRATIGRAPHY, STRUCTURE AND GEOCHRONOLOGY OF THE LAS CANADA CALDERA (TENERIFE, CANARY-ISLANDS)

After a long period of subaerial fissure-fed extrusions of basaltic magmas (similar to 12 to > 3 Ma) volcanic activity was then concentrated in the central part of Tenerife. Phonolitic magma chambers formed and a central volcanic complex was constructed (the Las Canadas edifice). The formation of a large depression (the Las Canadas caldera) truncated the top of the edifice. The active twin strato-cones Teide-Pico Viejo are sited in this depression. The history of the Las Canadas caldera and edifice are established from stratigraphy, geochronology (K-Ar dates) and volcanological studies. Two different groups are recognized, separated by a major unconformity. The Lower Group is dated at 2 to 3 Ma and includes the products of several volcanic centres, which together represent several cycles. The Upper Group ranges from 1.56 to 0.17 Ma and includes three different formations representing three long-term (similar to 100 to 300 Ka) volcanic cycles. The periods of dormancy between each formation were of similar to 120 to 250 Ka duration. The Las Canadas caldera is a multicyclic caldera which formed over the period 1.18-0.17 Ma. Each cycle of activity represented by a formation culminated in caldera collapse which affected different sectors of the Las Canadas edifice. Geological observation and geochronology support an origin by collapse into a magma chamber. The minimum volume of pyroclastic ejecta is substantially greater than the present caldera depression volume (45 km(3)), but approaches the inferred volume of the original caldera depression (> 140 km(3)). After the formation of the caldera, sector collapses could also occur at the northern flank of the volcano causing the disappearance of the northern side of the caldera wall.