The mineral chemistry and petrology of Tertiary pitchstones from Scotland

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Authors:Preston, R. J.; Hole, M. J.; Still, J.; Patton, H.
Author Affiliations:Primary:
University of Aberdeen, Department of Geology and Petroleum Geology, Aberdeen, United Kingdom
Volume Title:Transactions of the Royal Society of Edinburgh: Earth Sciences
Source:Transactions of the Royal Society of Edinburgh: Earth Sciences, Vol.89(Part 2), p.95-111. Publisher: Royal Society of Edinburgh, Edinburgh, United Kingdom. ISSN: 0263-5933
Publication Date:1998
Note:In English. 63 refs.; illus., incl. 9 tables, sketch map
Summary:Sub-silicic to silicic pitchstones are widespread throughout the British Tertiary Igneous Province (BTIP), with examples being found at all the major igneous centres. Both highly porphyritic and almost completely aphyric varieties occur, and take the form of sills, dykes and lava flows. Here we present previously unreported mineral chemistry data on phenocryst and microcrystallite populations from a number of pitchstones from throughout the BTIP. Phenocryst assemblages are completely anhydrous, comprising mixtures of plagioclase, sanidine, fayalite, orthopyroxene, pigeonite, ferroaugite, ferrohedenbergite and quartz. Microcrystallite assemblages are also diverse, consisting of sanidine, ferrohedenbergite, fayalite and, occasionally, almost pure end-member ferrosilite, as well as hydrous phases such as ferrohornblende and biotite. Textural and mineral chemistry observations support interpretations derived from whole-rock and residual glass major element analyses, together with whole-rock trace element and the available Sr-Nd-Pb isotope data, that the Tertiary pitchstones of Scotland are either the products of intimate mixing between a range of basaltic magmas with hydrous crustal melts, or were formed by the crustal contamination of basaltic magmas.
Subsections:Igneous petrology
Subjects:Basaltic composition; Cenozoic; Chemical composition; Crust; Geochemistry; Glasses; Igneous rocks; Intrusions; Lava; Magmas; Major elements; Mineral assemblages; Mineral composition; Mixing; Petrography; Phenocrysts; Pitchstone; Spectra; Tertiary; Textures; Trace elements; Volcanic rocks; Whole rock; X-ray fluorescence spectra; Ardnamurchan; Argyllshire Scotland; Arran; Europe; Great Britain; Hebrides; Highland region Scotland; Inner Hebrides; Inverness-shire Scotland; Mull Island; Raasay; Scotland; United Kingdom; Western Europe; Eigg Island; Strathclyde region Scotland
Abstract Numbers:99M/2142
Record ID:1999024814
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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