Magma genesis by rifting of oceanic lithosphere above anomalous mantle: Terceira Rift, Azores.

Beier C, Haase K, Abouchami W, Krienitz MS, Hauff F (2008)

Publication Language: English

Publication Type: Journal article

Publication year: 2008

Journal

Geochemistry Geophysics Geosystems American Geophysical Union (AGU)

Publisher: American Geophysical Union (AGU)

Pages Range: doi: 10.1029/2008GC002112

DOI: 10.1029/2008GC002112

Abstract

The Terceira Rift formed relatively recently (̃1 Ma ago) by rifting of the old oceanic lithosphere of the Azores Plateau and is currently spreading at a rate of 2-4mm/a. Together with the Mid-Atlantic Ridge, the Terceira Rift forms a triple junction that separates the Eurasian, African, and American Plates. Four volcanic systems (São Miguel, João de Castro, Terceira, Graciosa), three of which are islands, are distinguished along the axis and are separated by deep avolcanic basins similar to other ultraslow spreading centers. The major element, trace element and Sr-Nd-Pb isotope geochemistry of submarine and subaerial lavas display large along-axis variations. Major and trace element modeling suggests melting in the garnet stability field at smaller degrees of partial melting at the easternmost volcanic system (São Miguel) compared to the central and western volcanoes, which appear to be characterized by slightly higher melting degrees in the spinel/garnet transition zone. The degrees of partial melting at the Terceira Rift are slightly lower than at other ultraslow mid-ocean ridge spreading axes (Southwest Indian Ridge, Gakkel Ridge) and occur at greater depths as a result of the melting anomaly beneath the Azores. The combined interaction of a high obliquity, very slow spreading rates, and a thick preexisting lithosphere along the axis probably prevents the formation and eruption of larger amounts of melt along the Terceira Rift. However, the presence of ocean islands requires a relatively stable melting anomaly over relatively long periods of time. The trace element and Sr-Nd-Pb isotopes display individual binary mixing arrays for each volcanic system and thus provide additional evidence for focused magmatism with no (or very limited) melt or source interaction between the volcanic systems. The westernmost mantle sources beneath Graciosa and the most radiogenic lavas from the neighboring Mid-Atlantic Ridge suggest a mantle flow from Graciosa toward the Mid-Atlantic Ridge and hence a flux of mantle material from one spreading axis into the other. The Terceira Rift represents a unique oceanic rift system situated within the thickened, relatively old oceanic lithosphere and thus exhibits both oceanic and continental features. © 2008 by the American Geophysical Union.

Authors with CRIS profile

Christoph Beier Lehrstuhl für Endogene Geodynamik (LEG) Karsten Haase Lehrstuhl für Endogene Geodynamik (LEG)

Involved external institutions

Max-Planck-Institut für Chemie (Otto Hahn Institut) / Max Planck Institute for Chemistry DE Germany (DE) Christian-Albrechts-Universität zu Kiel DE Germany (DE) GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel DE Germany (DE)

How to cite

APA:

Beier, C., Haase, K., Abouchami, W., Krienitz, M.-S., & Hauff, F. (2008). Magma genesis by rifting of oceanic lithosphere above anomalous mantle: Terceira Rift, Azores. Geochemistry Geophysics Geosystems, doi: 10.1029/2008GC002112. https://doi.org/10.1029/2008GC002112

MLA:

Beier, Christoph, et al. "Magma genesis by rifting of oceanic lithosphere above anomalous mantle: Terceira Rift, Azores." Geochemistry Geophysics Geosystems (2008): doi: 10.1029/2008GC002112.

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