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 P alma, 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 edif ice. 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 ed ifices, and they were followed by eruptions between 0.71 and 0.65 Ma w hich built a new edifice that partly filled the depressions thus creat ed. The Caldera de Taburiente constitutes the eroded remnants of the d epression formed in the northern shield. From 0.65 Ma to present, acti vity has been restricted to the N-S ridge, which has continued to grow southwards. There was a general N-S migration of volcanic activity wi th time, but in the shield the trend was northwest to southeast. Erupt ive rates seem to have been fairly constant during the different erupt ive phases considered, between 0.15 and 0.37 km3/ka. A very similar su ccession of constructive and destructive episodes has been obtained fo r the neighboring island of Hierro, but in this case the activity star ted around 0.8 Ma and eruptive rates were about 0.5 kM3/ka.