Microgranitoid enclave swarms in granitic plutons, central Sierra Nevada, California

O. T. Tobisch*, B. A. McNulty, R. H. Vernon

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    65 Citations (Scopus)

    Abstract

    Microgranitoid enclaves are common in granitic plutons worldwide, occurring individually and in homogeneous or heterogeneous swarms. Three plutons in the central Sierra Nevada batholith contain swarms with mostly heterogeneous suites of enclaves in the intermediate composition range, and occur in a number of two-dimensional shapes, specifically as dikes, small rafts, lenses, pipe/vortices and large massive shapes. Swarms are characterized by various features, including the nature of their boundary with the host, their planar or non-planar character, internal geometry, density of enclave packing, presence or absence of schlieren and crystal aggregates, and axial ratios and degree of preferred alignment of enclaves. We propose that heterogeneous enclave swarms form by one, or some combination of, the following mechanisms: (1) velocity-gradient sorting parallel or normal to the flow, (2) gravitational sorting or (3) break-up of heterogeneous dikes. Common sites where enclave swarms form include pluton margins or internal viscosity walls, within fractures, and near the pluton roof.

    Original languageEnglish
    Pages (from-to)321-339
    Number of pages19
    JournalLithos
    Volume40
    Issue number2-4
    Publication statusPublished - Jul 1997

    Keywords

    • Granites
    • Mafic inclusion accumulation
    • Mechanisms

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