The mineral chemistry and petrology of Tertiary pitchstones from Scotland

R J Preston, M J Hole, J Still, H Patton

Research output: Contribution to journalArticle

7 Citations (Scopus)

Abstract

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.

Original languageEnglish
Pages (from-to)95-111
Number of pages17
JournalTransactions of the Royal Society of Edinburgh. Earth Sciences
Volume89
Publication statusPublished - 1998

Keywords

  • basalt
  • BTIP
  • crustal melts
  • crystallites
  • disequilibrium phenocrysts
  • glass
  • magma mixing
  • crustal contamination processes
  • fractional
  • feldspar crystallization
  • igneous complex
  • felsic magmas
  • NW Scotland
  • olivine
  • Skye
  • geochemistry
  • Isle

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