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Petrogenetic Evolution, Geometries and Intrusive Styles of the Early Cenozoic Saucer-Shaped Sills of the Faroe Islands

HANSEN, JOGVAN (2011) Petrogenetic Evolution, Geometries and Intrusive Styles of the Early Cenozoic Saucer-Shaped Sills of the Faroe Islands. Doctoral thesis, Durham University.

PDF (Ph.D. thesis in geology 2011 by Jogvan Hansen) - Accepted Version
[img]Plain Text (Subsidiary material in support of thesis/candidate - references to research journal papers) - Supplemental Material


Geometries of sills intruded into the lava pile of the Faroe Island Basalt Group (FIBG), which were targeted in this study, were mostly recorded by conventional mapping methods where measured distances and positions were plotted onto accurate topographic maps aided by the use of high-quality photos of relevant outcrops. These data were subsequently used to manually plot 2D profiles along selected tracks and to produce electronic 3D maps using ArcGIS software.
The general geometries of the investigated sills, measured at lateral scales ranging from a few metres to a few kilometres and at vertical scales ranging from a few metres to a few hundred metres, differ somewhat from typical sill geometries reported previously for sills intruded into sedimentary successions. The ubiquitous saucer-shapes of the sills from this study, which generally curve upwards in a gradual manner from inner sub-horizontal sections to steeper outer margins, contrast with the common angular transitions from inner sub-horizontal to outer steeper sections of sills reported from sedimentary host-rocks. In this thesis we explore possible alternatives to already existing theories on sill emplacement in sedimentary successions.
Major and trace element compositions for samples representing most of the sills exposed in the Faroe Islands have been determined by means of XRF and ICP-MS analyses. Geochemically most of these sills can be grouped into two main categories characterised either by high or by low TiO2 contents. Different sorts/types of metasomatism of source rocks to high-TiO2 versus low-TiO2 sills are indicated by different Nb and Ta anomalies. Modelling by means of REE and other trace elements suggest that much of the compositional differences between these two main categories can be explained by various degrees of partial melting of broadly similar mantle sources. Additional fractionation and accumulation of plagioclase modified some of the melts that gave rise to the actual sills. The initial partial melting event probably occurred at depths slightly shallower than the lower limit of the garnet stability field at ~85 km while plagioclase crystallisation/accumulation most likely occurred at depths shallower than ~18 km. Isotopic compositions may point to very slight contamination of some sills with crustal material.

Item Type:Thesis (Doctoral)
Award:Doctor of Philosophy
Keywords:"North Atlantic Igneous Province" "Faroe Islands" "Saucer-shaped sills" "Flood basalts" "Distinct partial melting" "Fractional crystallisation and accumulation" "Crustal contamination"
Faculty and Department:Faculty of Science > Earth Sciences, Department of
Thesis Date:2011
Copyright:Copyright of this thesis is held by the author
Deposited On:26 Jun 2012 12:35

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