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Geochemical and geochronological constraints on the evolution of the Azores Plateau

By
Christoph Beier
Christoph Beier
Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), GeoZentrum Nordbayern, Schloßgarten 5, D-91054 Erlangen, Germany, and Max-Planck-Institut für Chemie (Otto-Hahn-Institut), Abteilung Geochemie, Postfach 3060, 55020 Mainz, Germany
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Karsten M. Haase
Karsten M. Haase
Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), GeoZentrum Nordbayern, Schloßgarten 5, D-91054 Erlangen, Germany
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Wafa Abouchami
Wafa Abouchami
Max-Planck-Institut für Chemie (Otto-Hahn-Institut), Abteilung Geochemie, Postfach 3060, 55020 Mainz, Germany
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Published:
May 01, 2015

We report new 40Ar/39Ar ages on submarine lavas from the Azores Plateau that yield ages of 6–4.9 Ma and 1.5 Ma to Holocene. An additional sample from the eastern plateau gives an age of 39 Ma. Thus, at least two, possibly even three eruptive phases occurred in the past 39 m.y. The lava compositions range from slightly incompatible trace element–enriched tholeiites to highly enriched alkali basalts similar to those erupted on the Azores islands. The less enriched tholeiitic lavas occur in the westernmost plateau and formed by relatively high degrees of partial melting. The highly enriched alkali basalts appear to be restricted to local volcanic structures, implying different phases of intraplate volcanism that are possibly related to the jump of the ultraslow-spreading Terceira Rift within the Azores Plateau. The abundance and widespread spatial distribution of volcanism with ages of 6–4.9 Ma in subaerial and submarine lavas implies the presence of a thermal or chemical melting anomaly and a period of enhanced volcanism that led to tholeiitic volcanism following, and being followed by, alkali-basaltic volcanism. The small-scale (Sr-)Nd-Pb isotopic heterogeneity of the Azores plume source implies limited mixing in the mantle, in contrast to observations made on other plume-related settings such as the Galapagos. We suggest that the Azores Plateau initially formed from interaction between geochemically and thermally anomalous mantle, possibly a small mantle plume, arriving underneath the lithosphere, and the local plate tectonics, i.e., the Terceira Rift axis, provided ascent paths for the generated magmas.

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GSA Special Papers

The Origin, Evolution, and Environmental Impact of Oceanic Large Igneous Provinces

Clive R. Neal
Clive R. Neal
Department of Civil & Environmental Engineering & Earth Sciences, 156 Fitzpatrick Hall, University of Notre Dame, Notre Dame, Indiana 46556, USA
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William W. Sager
William W. Sager
Department of Earth and Atmospheric Sciences, University of Houston, Houston, Texas 77204-5007, USA
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Takashi Sano
Takashi Sano
Department of Geology and Paleontology, National Museum of Nature and Science, Tsukuba 305-0005, Japan
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Elisabetta Erba
Elisabetta Erba
Department of Earth Sciences, Università degli Studi di Milano, 20133 Milan, Italy
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Geological Society of America
Volume
511
ISBN print:
9780813725116
Publication date:
May 01, 2015

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