San Miguel de La Palma — A volcanic island in section

Abstract

San Miguel de La Palma is the northwestern island in the Canary group. An extensive vertical section through the island can be seen in the deep Caldera de Taburiente in the north of the island. The island in divided into four units: (1) the floor of the Caldera de Taburiente, (2) the remainder of the old volcano Tuburiente (El Time formation), (3) the El Paso tectonic basin, and (4) the Cumbre Vieja mountain land that forms the southern part of the island. The Caldera Floor formation consists of (1) a variety of deformed metamorphosed and metasomatised basaltic and trachytic rocks, (2) metamorphosed pyroclasts, and (3) bodies of gabbro, troctolite, wehrlite, dunite, alkalic gabbro and essexite. These rocks are cut by mafic and bostonitic dykes. The lavas and pyroclasts of the El Time formation overlie the Caldera Floor formation and generally dip outwards and away from the caldera. Alkalic basalts are the main lava type, followed by trachybasalts with lesser amounts of trachyandesite, trachyte and phonolite. The El Paso tectonic basin is a subsided segment of the volcano Tuburiente, and consists mainly of El Time formation rocks. All the major recorded eruptions have issued from the Cumbre Vieja mountain land. The eruptive products found in the mountain land range from alkalic basalt to phonolite. Pyroclasts and phonolitic lavas are more common than in the earlier formations. Tall spires of hauyne phonolite are found in a number of localities. The eruptive products now found on La Palma are believed to have developed from an alkaline basalt magma. Under normal circumstances this magma rose rapidly from the upper mantle, and erupted; however, when the La Palma volcanic edifice was large enough to accommodate a magma chamber differentiation took place; silica was removed, and both ultramafic cumulates, and trachytic and phonolitic differentiates were produced.