The petrology and geochemistry of Caledonian basic bodies of NE Scotland and Connemara

Mullen, Robert Patrick (2002). The petrology and geochemistry of Caledonian basic bodies of NE Scotland and Connemara. University of Birmingham. Ph.D.

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The petrography, mineralogy and whole rock chemistry of a suite of Grampian-age, synorogenic basic plutons in Scotland and Connemara are examined. These bodies display mineralogical and chemical features consistent with having evolved by fractionation combined with melting and assimilation of their pelitic country rocks. Olivine compositions range from F0914 to FoL2, with pyroxenes and other ferromagnesian phases showing concomitant extreme iron enrichment. Plagioclase feldspar ranges from An96 6 to An28 5 in composition, while apatite, zircon and quartz are present as late crystallising phases. Trends seen in the main silicate phases, and in whole rock chemistry, suggest a tholeiitic fractionation path, while evidence is seen in the central bodies for the presence of more than one phase of intrusive activity.
Modelling of the evolution of selected trends is consistent with the levels of fractionation and contamination predicted from the chemistry and petrography, with the shape of ‘spider’ and REE plots largely controlled by this contamination, and by the presence of cumulus accessory phases. Modelled levels of contamination vary from ~14 to 17% during the fractionation of the Middle Zones of the northeastern and central intrusions, and decreases to as little as ~3.5% with increasing evolution in the central intrusions.
A set of granular gabbros occurring within the Insch intrusion has been identified as resembling the probable parental magmas to the ‘Younger’ Basics. These samples are mineralogically and chemically distinct from the main cumulate sequence, and exhibit chemical properties (high A12O3 content; low 87Sr/86Sr ratios; flat ‘spider’ and REE plots) consistent with the likely parental magmas responsible for this main cumulate sequence. It is suggested that they represent a partial mantle melt, with an added slab component indicating derivation in an arctype setting.

Type of Work: Thesis (Doctorates > Ph.D.)
Award Type: Doctorates > Ph.D.
Licence: All rights reserved
College/Faculty: Schools (1998 to 2008) > School of Geography, Earth & Environmental Sciences
School or Department: School of Earth Sciences
Funders: None/not applicable
Subjects: Q Science > QE Geology


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