The petrology of the tholeiites through melilite nephelinites on Gran Canaria, Canary Islands: crystal fractionation, accumulation and depths of melting.

Hoernle, Kaj and Schmincke, Hans-Ulrich (1993) The petrology of the tholeiites through melilite nephelinites on Gran Canaria, Canary Islands: crystal fractionation, accumulation and depths of melting. Open Access Journal of Petrology, 34 . pp. 573-597. DOI 10.1093/petrology/34.3.573.

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Abstract

We report major and trace element X-ray fluorescence (XRF) data for mafic volcanics covering the
15-Ma evolution of Gran Canaria, Canary Islands. The Miocene (12-lS^Ma) and Pliocene-Quaternary
(0-6 Ma) mafic volcanics on Gran Canaria include picrites, tholeiites, alkali basalts, basanites,
nephelinites, and melilite nephelinites. Olivine±clinopyroxene are the major fractionating or
accumulating phases in the basalts. Plagioclase, Fe-Ti oxide, and apatite fractionation or
accumulation may play a minor role in the derivation of the most evolved mafic volcanics. The
crystallization of clinopyroxene after olivine and the absence of phenocrystic plagioclase in the
Miocene tholeiites and in the Pliocene and Quaternary alkali basalts and basanites with MgO>6
suggests that fractionation occurred at moderate pressure, probably within the upper mantle. The
presence of plagioclase phenocrysts and chemical evidence for plagioclase fractionation in the Miocene
basalts with MgO<6 and in the Pliocene tholeiites is consistent with cooling and fractionation at
shallow depth, probably during storage in lower-crustal reservoirs. Magma generation at pressures in
excess of 3-0-3-5 GPa is suggested by (a) the inferred presence of residual garnet and phlogopite and (b)
comparison of FeO1 cation mole percentages and the CIPW normative compositions of the mafic
volcanics with results from high-pressure melting experiments. The Gran Canaria mafic magmas were
probably formed by decompression melting in an upwelling column of asthenospheric material, which
encountered a mechanical boundary layer at ~ 100-km depth.

Document Type: Article
Keywords: NEUTRON-ACTIVATION ANALYSIS; TRACE-ELEMENT GEOCHEMISTRY; BASALT PETROGENESIS; ZIRCON SATURATION; FATAGA FORMATIONS; REUNION ISLAND; DRY PERIDOTITE; UPPER MANTLE; EVOLUTION; ROCKS
Research affiliation: OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1093/petrology/34.3.573
ISSN: 0022-3530
Date Deposited: 29 Oct 2013 09:40
Last Modified: 02 Mar 2018 11:20
URI: http://oceanrep.geomar.de/id/eprint/22295

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