Evolution of parental magmas of Miocene shield basalts of Gran Canaria (Canary Islands): constraints from crystal,melt and fluid inclusions in minerals |
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| Authors: | A A Gurenko Thor H Hansteen Hans-Ulrich Schmincke |
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| Institution: | (1) GEOMAR Research Center, Department of Volcanology and Petrology, Wischhofstrasse 1-3, D-24148 Kiel, Germany, DE;(2) Vernadsky Institute of Geochemistry, Russian Acad. Sci., Kosigin str. 19, 117 975 Moscow, Russia, RU;(3) CRPG-CNRS, BP 20, F-54501 Vandoeuvre-lès-Nancy Cedex, France, FR |
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| Abstract: | Picritic units of the Miocene shield volcanics on Gran Canaria, Canary Islands, contain olivine and clinopyroxene phenocrysts
with abundant primary melt, crystal and fluid inclusions. Composition and crystallization conditions of primary magmas in
equilibrium with olivine Fo90-92 were inferred from high-temperature microthermometric quench experiments, low-temperature microthermometry of fluid inclusions
and simulation of the reverse path of olivine fractional crystallization based on major element composition of melt inclusions.
Primary magmas parental for the Miocene shield basalts range from transitional to alkaline picrites (14.7–19.3 wt% MgO, 43.2–45.7
wt% SiO2). Crystallization of these primary magmas is believed to have occurred over the temperature range 1490–1150° C at pressures
≈5 kbar producing olivine of Fo80.6-90.2, high-Ti chrome spinel Mg/ (Mg+Fe2+)=0.32–0.56, Cr/(Cr+Al)=0.50–0.78, 2.52–8.58 wt% TiO2], and clinopyroxene Mg/(Mg+Fe)=0.79–0.88, Wo44.1-45.3, En43.9-48.0, Fs6.8-11.0] which appeared on the liquidus together with olivine≈Fo86. Redox conditions evolved from intermediate between the QFM and WM buffers to late-stage conditions of NNO+1 to NNO+2. The
primary magmas crystallized in the presence of an essentially pure CO2 fluid. The primary magmas originated at pressures >30 kbar and temperatures of 1500–1600° C, assuming equilibrium with mantle
peridotite. This implies melting of the mantle source at a depth of ≈100 km within the garnet stability field followed by
migration of melts into magma reservoirs located at the boundary between the upper mantle and lower crust. The temperatures
and pressures of primary magma generation suggest that the Canarian plume originated in the lower mantle at depth ≈900 km
that supports the plume concept of origin of the Canary Islands.
Received: 23 October 1995/Accepted: 21 February 1996 |
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