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Resolving problems with the origin of Las Cañadas caldera (Tenerife, Canary Islands): Los Roques de García Formation—Part of a major debris avalanche or an in situ, stratified, edifice-building succession?

By
Joan Martí
Joan Martí
Institute of Earth Sciences “Jaume Almera,” Consejo Superior de Investigaciones Científicas, Barcelona 08028, Spain
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Carlos Soriano
Carlos Soriano
Institute of Earth Sciences “Jaume Almera,” Consejo Superior de Investigaciones Científicas, Barcelona 08028, Spain
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Inés Galindo
Inés Galindo
Oficina de Proyectos de Las Palmas de Gran Canaria, Instituto Geológico y Minero de España (IGME), Las Palmas de Gran Canaria 35003, Spain
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Raymond A.F. Cas
Raymond A.F. Cas
School of Geosciences, Monash University, Clayton, Victoria 3800, Australia
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Published:
April 01, 2010

Las Cañadas caldera complex, on Tenerife, Canary Islands, truncated the construction of Las Cañadas edifice, a central composite volcanic complex formed after a main period of basaltic shield construction. The origin of the present Las Cañadas caldera complex is still a matter of considerable debate between two contrasting hypotheses, vertical (caldera forming) or lateral (landslide) collapse. However, there is increasing evidence that a long history of explosive phonolitic volcanism, including several caldera episodes, characterized the construction of Las Cañadas edifice. Los Roques de García forms a large spur that divides the Las Cañadas caldera complex into two morphological depressions. The sequence of rocks exposed along the spur consists of several formations that from base to top include: Los Roques de García Formation, Los Azulejos Formation, and the lower part of the Ucanca Formation. Los Roques de García Formation occupies the main part of Los Roques de García spur and includes proximal facies of pyroclastic (Lower Member) and sedimentary (epiclastic) (Upper Member) deposits, predominantly breccias, all of which are intruded by a dense network of phonolitic dikes and necks. Pyroclastic deposits mostly correspond to coignimbrite lag breccias, lithic-rich ignimbrites, and minor surge and ash-fall beds. Epiclastic rocks mainly include poorly to well-stratified, proximal debrisflows breccias deposited in an alluvial-fan environment, with some interbedded pyroclastic and epiclastic sandstone and conglomerate units. The central sector of Los Roques de García spur is highly fractured due to the movement of several normal faults, thus conferring a chaotic aspect to that zone. Strong hydrothermal alteration also has affected some sectors of Los Roques de García spur, enhancing this chaotic appearance. New detailed mapping and stratigraphic logging have been crucial to interpreting the nature and stratigraphy of Los Roques de García rocks, which represent two fundamental aspects for the interpretation of the origin and evolution of Las Cañadas caldera. Los Roques de García spur exhibits a stratigraphy that is concordant with the rest of Las Cañadas caldera wall and corresponds to the lower part (Lower Group) of Las Cañadas edifice, without having any relation to latter explosive episodes responsible for the deposition of its upper part (Upper Group). Lithological, sedimentological, and volcanological characteristics of Los Roques de García rocks allow them to be interpreted either as a former Las Cañadas intracaldera sequence or as the apron of an older stratovolcano, in contrast with previous interpretations, which have suggested that they correspond to the products of a major debris avalanche event that contributed to the formation of the present caldera.

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Contents

GSA Special Papers

Stratigraphy and Geology of Volcanic Areas

Gianluca Groppelli
Gianluca Groppelli
Consiglio Nazionale delle Ricerche, Istituto per la Dinamica dei Processi Ambientali, Sezione di Milano, Milano, Italy
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Lothar Viereck-Goette
Lothar Viereck-Goette
Institut für Geowissenschaften, Friedrich-Schiller-Universität Jena, Jena, Germany
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Geological Society of America
Volume
464
ISBN print:
9780813724645
Publication date:
April 01, 2010

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