Basaltic melt evolution of the Hengill volcanic system, SW Iceland, and evidence for clinopyroxene assimilation in primitive tholeiitic magmas

Journal Article · Mon Sep 10 00:00:00 EDT 1990 · Journal of Geophysical Research; (USA)

DOI:https://doi.org/10.1029/JB095iB10p15893· OSTI ID:5888540

Troennes, R G ^[1]

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1. Univ. of Iceland, Reykjavik (Iceland)

The thick oceanic crust of Iceland is formed by tholeiitic central volcanoes arranged in en echelon patterns along the 40-50 km wide rift zones. The Hengill central volcano in the southwestern rift zone has produced 25-30 km{sup 3} of hyaloclastites and lava during the last 0.11 m.y., with maximum productivity during the isostatic rebound following the degalciations 0.13 and 0.01 m.y. ago. The petrographic relations of pillow rim and hyaloclastite glass indicate that the basaltic melts were saturated with olivine and plagioclase, except for the most primitive ones that were undersaturated with plagioclase. Saturation with clinopyroxene was reached in some of the intermediate and evolved basaltic melts. Corroded and partly resorbed crystals of clinopyroxene and partly disintegrated gabbro nodules with resorbed clinopyroxene indicate that selective assimilation contributed to the evolution of the most primitive melts. The intermediate and evolved basaltic glass compositions fall along the low-pressure cotectic for mid-ocean ridge basalt (MORB) compositions saturated with olivine, plagioclase, and clinopyroxene, but the primitive glasses fall well inside the low-pressure olivine + plagioclase primary phase volume. The dense picritic magmas were driven to the surface by magmatic overpressure in the mantle at an early deglaciation stage characterized by the absence of large, trapping magma chambers in the lower crust. The assimilation of clinopyroxene in these melts could proceed by direct contact with the solidified cumulate sequences and gabbro intrusions. Clinopyroxene assimilation in combination with olivine fractionation may also contribute to the chemical evolution of some of the most primitive MORB magmas.

• OSTI ID: 5888540
• Journal Information: Journal of Geophysical Research; (USA), Vol. 95:B10; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
ICELAND
VOLCANOES
GEOCHEMISTRY
ALUMINIUM OXIDES
ANORTHOSITES
BASALT
CALCIUM OXIDES
CORRELATIONS
EARTH MANTLE
FRACTIONATION
GLACIERS
GLASS
LAVA
MAGMA
MID-ATLANTIC RIDGE
OCEANIC CRUST
OLIVINE
ORIGIN
PETROGRAPHY
PRESSURIZATION
PRODUCTION
PYROXENES
RIFT ZONES
SATURATION
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
CALCIUM COMPOUNDS
CHALCOGENIDES
CHEMISTRY
DEVELOPING COUNTRIES
EARTH CRUST
EUROPE
GABBROS
GEOLOGIC STRUCTURES
IGNEOUS ROCKS
IRON COMPOUNDS
IRON SILICATES
ISLANDS
MAGNESIUM COMPOUNDS
MAGNESIUM SILICATES
MINERALS
OXIDES
OXYGEN COMPOUNDS
PLUTONIC ROCKS
ROCKS
SEPARATION PROCESSES
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
VOLCANIC ROCKS
WESTERN EUROPE
580000* - Geosciences