Abstract

The superimposition of Barrovian-type metamorphism on low-pressure contact aureoles in magmatic arcs is subject to the kinetic constraints of temperature and influx of H2O and may be cryptically developed or not at all. The spatial distribution of detectable overprint will reflect these kinetic factors rather than the geometry of the imposed load. Many of the features believed indicative of magma loading, including apparent steep baric gradients, may be produced in this way. On the basis of adding areas of cryptic metamorphism to the area of obvious Barrovian overprint on the northeast side of the Mount Stuart batholith, we conclude that loading 2–3 m.y. after emplacement was probably much more extensive (sheetlike) than believed previously.

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