Skip to Main Content
Book Chapter

Ignimbrite stratigraphy and chronology on Terceira Island, Azores

By
Ralf Gertisser
Ralf Gertisser
Earth Sciences and Geography, School of Physical and Geographical Sciences, Keele University, Keele, ST5 5BG, UK
Search for other works by this author on:
Stephen Self
Stephen Self
Department of Earth and Environmental Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
Search for other works by this author on:
João L. Gaspar
João L. Gaspar
Centro de Vulcanologia e Avaliação de Riscos Geológicos, Universidade dos Açores, 9501-801 Ponta Delgada, Açores, Portugal
Search for other works by this author on:
Simon P. Kelley
Simon P. Kelley
Department of Earth and Environmental Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
Search for other works by this author on:
Adriano Pimentel
Adriano Pimentel
Centro de Vulcanologia e Avaliação de Riscos Geológicos, Universidade dos Açores, 9501-801 Ponta Delgada, Açores, Portugal
Search for other works by this author on:
Jost Eikenberg
Jost Eikenberg
Division for Radiation Protection and Safety, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
Search for other works by this author on:
Tiffany L. Barry
Tiffany L. Barry
Department of Earth and Environmental Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
Search for other works by this author on:
José M. Pacheco
José M. Pacheco
Centro de Vulcanologia e Avaliação de Riscos Geológicos, Universidade dos Açores, 9501-801 Ponta Delgada, Açores, Portugal
Search for other works by this author on:
Gabriela Queiroz
Gabriela Queiroz
Centro de Vulcanologia e Avaliação de Riscos Geológicos, Universidade dos Açores, 9501-801 Ponta Delgada, Açores, Portugal
Search for other works by this author on:
Marika Vespa
Marika Vespa
Mineralogy and Environments, LGCA, Université Joseph Fourier and Centre National de la Recherche Scientifique, 38041 Grenoble Cedex 9, France
Search for other works by this author on:
Published:
April 01, 2010

Ignimbrites are relatively rare on mid-oceanic volcanic islands, but they occur on at least three of the nine Azorean islands—São Miguel, Faial, and Terceira. Ignimbrites on Terceira, which are mostly comenditic trachyte in composition, constitute a significant portion of the island's volcanic stratigraphy exposed primarily in cliff sections along the southern and northern coastlines. The base of the most recent group of deposits, called the Upper Terceira Group, is marked by the Lajes-Angra Ignimbrite, an extensive ignimbrite sheet produced during the latest ignimbrite-forming episode ~20–23 k.y. ago. The Lower Terceira Group consists of ignimbrites and interstratified pyroclastic fall deposits and lava flows predating the Lajes-Angra Ignimbrite. Including the Lajes-Angra Ignimbrite, the exposed volcanic succession on Terceira includes at least seven formations containing ignimbrites plus two isolated exposures of other pyroclastic density current deposits (a spatter flow and a block-and-ash-flow–like deposit). Most of these are from Pico Alto or, possibly, Guilherme Moniz, the middle pair of central volcanoes of the four that form Terceira. Radiocarbon ages complemented by 40Ar/39Ar age determinations on anorthoclase crystals from several ignimbrites suggest a narrow period of ignimbrite-forming volcanism on Terceira dating from ca. 86 ka to ca. 20–23 ka, which followed a period of predominantly effusive basaltic to trachytic/rhyolitic activity. However, a recurrence of ignimbrite volcanism on the island cannot be completely discounted. The results from this study also indicate that the 40Ar/39Ar method can be successfully applied to date anorthoclase crystals in volcanic rocks younger than 100 ka from Terceira, although it does not provide the same precision as radiocarbon dating at the younger age range of these volcanic rocks.

You do not currently have access to this article.
Don't already have an account? Register

Figures & Tables

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
Search for other works by this author on:
Lothar Viereck-Goette
Lothar Viereck-Goette
Institut für Geowissenschaften, Friedrich-Schiller-Universität Jena, Jena, Germany
Search for other works by this author on:
Geological Society of America
Volume
464
ISBN print:
9780813724645
Publication date:
April 01, 2010

References

Related

A comprehensive resource of eBooks for researchers in the Earth Sciences

Related Articles
Close Modal
This Feature Is Available To Subscribers Only

Sign In or Create an Account

Close Modal
Close Modal