Igneous origin of K-feldspar megacrysts in deformed granite of the Papoose Flat Pluton, California, USA

R. H. Vernon*, S. R. Paterson

*Corresponding author for this work

    Research output: Contribution to journalArticle

    14 Citations (Scopus)

    Abstract

    Many points of evidence, especially igneous microstructures and structures resulting from solid-state deformation, indicate that K-feldspar megacrysts in deformed granites of the Papoose Flat pluton are residual phenocrysts, not porphyroblasts. Evidence of an igneous origin includes features such as crystal shapes, simple twinning, zonally arranged euhedral plagioclase inclusions, oscillatory compositional zoning, and local occurrence in microgranitoid enclaves. Evidence of solid-state deformation of the megacrysts (which is consistent with their existence prior to the mylonitic deformation) includes marginal recrystallization and neocrystallization, microcline twinning, marginal replacement by myrmekite, and recrystallized/neocrystallized "tails". Evidence of porphyroblastic growth, such as overgrown inclusion trails, is absent. This appears to be the situation in most felsic augen gneisses and mylonites.

    Original languageEnglish
    Pages (from-to)1-28
    Number of pages28
    JournalVisual Geosciences
    Volume7
    Issue number1
    DOIs
    Publication statusPublished - 2002

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