Structure and petrochemistry of the Hafnarfjall-Skarðsheiði Central Volcano and the surrounding basalt succession, W-Iceland
This research involves a study of a 2 km thick volcanic succession which accumulated during the opening stages of the precursor of the Reykjanes-Langjökull axial rift zone in W-Iceland, between 6-3 m.y. Following the initial accumulation of olivine tholeiite lavas, which lie unconformably on an old...
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The University of Edinburgh
1978
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ftunivedinburgh:oai:era.ed.ac.uk:1842/9679 2023-07-30T04:04:22+02:00 Structure and petrochemistry of the Hafnarfjall-Skarðsheiði Central Volcano and the surrounding basalt succession, W-Iceland Franzson, Hjalti Upton, Brian G. J. 1978 application/pdf http://hdl.handle.net/1842/9679 en eng The University of Edinburgh The University of Edinburgh. College of Science and Engineering http://hdl.handle.net/1842/9679 Volcanism Volcanic ash Basalt Geochemistry Iceland Thesis or Dissertation Doctoral PhD Doctor of Philosophy 1978 ftunivedinburgh 2023-07-09T20:30:38Z This research involves a study of a 2 km thick volcanic succession which accumulated during the opening stages of the precursor of the Reykjanes-Langjökull axial rift zone in W-Iceland, between 6-3 m.y. Following the initial accumulation of olivine tholeiite lavas, which lie unconformably on an older crustal basement 10-13 m.y.), a central volcano developed in the Hafnarfjall-Skarðsheiði area. It was active for some 1.5 m.y. and consists of four volcanic phases: I. The Brekkufjall phase is characterized by basaltic volcanism followed by voluminous and copious extrusions of differentiated rocks culminating in a sudden caldera collapse (c.5 km wide) in Brekkufjall. II. During the Hafnarfjall phase a thick extrusive sequence of basaltic to rhyolitic compositions accumulated, mainly fed by ENE fissures. During the gradual subsidence of the Hafnarfjall caldera (7 by 5 km) a marked decrease occurred in lava accumulation rate outside the caldera. Epicentres of three cone sheet swarms coincide in time and space with three basinal structures of this caldera. III. The Skarðsheiði phase is characterized by N-S fissuring and a marked bimodal basalt-rhyolite lava accumulation. IV. Remnants of the Heioarhorn phase include compositions ranging from basalts to rhyolites. The western boundary of the axial rift zone is marked by large intrusives, basalt flexuring, a sheet swarm and the disappearance of dyke swarms. The lenticular unit was later buried by lavas of the Hvalfjörður lenticular unit. Rocks of the central volcano follow the Þingrmúli trend, but is discontinuous in the basal tic andesite range. Basalts (frequently porphyritic) with relatively monotonous compositions and low LIL abundancies predominate during episodes of low extrusion rate whereas high elemental dispersion characterizes basalts of high extrusion rate episodes. The basalt compositions are believed to be controlled more by partial melting processes rather than by episodes of low-pressure fractionation. The differentiated rocks are considered to have ... Doctoral or Postdoctoral Thesis Iceland Edinburgh Research Archive (ERA - University of Edinburgh) Reykjanes ENVELOPE(-22.250,-22.250,65.467,65.467) Hvalfjörður ENVELOPE(-21.663,-21.663,64.376,64.376) Hafnarfjall ENVELOPE(-22.580,-22.580,66.408,66.408) Skarðsheiði ENVELOPE(-21.667,-21.667,64.467,64.467) |
institution |
Open Polar |
collection |
Edinburgh Research Archive (ERA - University of Edinburgh) |
op_collection_id |
ftunivedinburgh |
language |
English |
topic |
Volcanism Volcanic ash Basalt Geochemistry Iceland |
spellingShingle |
Volcanism Volcanic ash Basalt Geochemistry Iceland Franzson, Hjalti Structure and petrochemistry of the Hafnarfjall-Skarðsheiði Central Volcano and the surrounding basalt succession, W-Iceland |
topic_facet |
Volcanism Volcanic ash Basalt Geochemistry Iceland |
description |
This research involves a study of a 2 km thick volcanic succession which accumulated during the opening stages of the precursor of the Reykjanes-Langjökull axial rift zone in W-Iceland, between 6-3 m.y. Following the initial accumulation of olivine tholeiite lavas, which lie unconformably on an older crustal basement 10-13 m.y.), a central volcano developed in the Hafnarfjall-Skarðsheiði area. It was active for some 1.5 m.y. and consists of four volcanic phases: I. The Brekkufjall phase is characterized by basaltic volcanism followed by voluminous and copious extrusions of differentiated rocks culminating in a sudden caldera collapse (c.5 km wide) in Brekkufjall. II. During the Hafnarfjall phase a thick extrusive sequence of basaltic to rhyolitic compositions accumulated, mainly fed by ENE fissures. During the gradual subsidence of the Hafnarfjall caldera (7 by 5 km) a marked decrease occurred in lava accumulation rate outside the caldera. Epicentres of three cone sheet swarms coincide in time and space with three basinal structures of this caldera. III. The Skarðsheiði phase is characterized by N-S fissuring and a marked bimodal basalt-rhyolite lava accumulation. IV. Remnants of the Heioarhorn phase include compositions ranging from basalts to rhyolites. The western boundary of the axial rift zone is marked by large intrusives, basalt flexuring, a sheet swarm and the disappearance of dyke swarms. The lenticular unit was later buried by lavas of the Hvalfjörður lenticular unit. Rocks of the central volcano follow the Þingrmúli trend, but is discontinuous in the basal tic andesite range. Basalts (frequently porphyritic) with relatively monotonous compositions and low LIL abundancies predominate during episodes of low extrusion rate whereas high elemental dispersion characterizes basalts of high extrusion rate episodes. The basalt compositions are believed to be controlled more by partial melting processes rather than by episodes of low-pressure fractionation. The differentiated rocks are considered to have ... |
author2 |
Upton, Brian G. J. |
format |
Doctoral or Postdoctoral Thesis |
author |
Franzson, Hjalti |
author_facet |
Franzson, Hjalti |
author_sort |
Franzson, Hjalti |
title |
Structure and petrochemistry of the Hafnarfjall-Skarðsheiði Central Volcano and the surrounding basalt succession, W-Iceland |
title_short |
Structure and petrochemistry of the Hafnarfjall-Skarðsheiði Central Volcano and the surrounding basalt succession, W-Iceland |
title_full |
Structure and petrochemistry of the Hafnarfjall-Skarðsheiði Central Volcano and the surrounding basalt succession, W-Iceland |
title_fullStr |
Structure and petrochemistry of the Hafnarfjall-Skarðsheiði Central Volcano and the surrounding basalt succession, W-Iceland |
title_full_unstemmed |
Structure and petrochemistry of the Hafnarfjall-Skarðsheiði Central Volcano and the surrounding basalt succession, W-Iceland |
title_sort |
structure and petrochemistry of the hafnarfjall-skarðsheiði central volcano and the surrounding basalt succession, w-iceland |
publisher |
The University of Edinburgh |
publishDate |
1978 |
url |
http://hdl.handle.net/1842/9679 |
long_lat |
ENVELOPE(-22.250,-22.250,65.467,65.467) ENVELOPE(-21.663,-21.663,64.376,64.376) ENVELOPE(-22.580,-22.580,66.408,66.408) ENVELOPE(-21.667,-21.667,64.467,64.467) |
geographic |
Reykjanes Hvalfjörður Hafnarfjall Skarðsheiði |
geographic_facet |
Reykjanes Hvalfjörður Hafnarfjall Skarðsheiði |
genre |
Iceland |
genre_facet |
Iceland |
op_relation |
The University of Edinburgh. College of Science and Engineering http://hdl.handle.net/1842/9679 |
_version_ |
1772815742475960320 |