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

Abstract

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,more » 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.« less

Authors:
 [1]
  1. (Univ. of Iceland, Reykjavik (Iceland))
Publication Date:
OSTI Identifier:
5888540
Resource Type:
Journal Article
Journal Name:
Journal of Geophysical Research; (USA)
Additional Journal Information:
Journal Volume: 95:B10; Journal ID: ISSN 0148-0227
Country of Publication:
United States
Language:
English
Subject:
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

Citation Formats

Troennes, R.G. Basaltic melt evolution of the Hengill volcanic system, SW Iceland, and evidence for clinopyroxene assimilation in primitive tholeiitic magmas. United States: N. p., 1990. Web. doi:10.1029/JB095iB10p15893.
Troennes, R.G. Basaltic melt evolution of the Hengill volcanic system, SW Iceland, and evidence for clinopyroxene assimilation in primitive tholeiitic magmas. United States. doi:10.1029/JB095iB10p15893.
Troennes, R.G. Mon . "Basaltic melt evolution of the Hengill volcanic system, SW Iceland, and evidence for clinopyroxene assimilation in primitive tholeiitic magmas". United States. doi:10.1029/JB095iB10p15893.
@article{osti_5888540,
title = {Basaltic melt evolution of the Hengill volcanic system, SW Iceland, and evidence for clinopyroxene assimilation in primitive tholeiitic magmas},
author = {Troennes, R.G.},
abstractNote = {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.},
doi = {10.1029/JB095iB10p15893},
journal = {Journal of Geophysical Research; (USA)},
issn = {0148-0227},
number = ,
volume = 95:B10,
place = {United States},
year = {1990},
month = {9}
}