Rock pressure vs. fluid pressure as a controlling influence on mineral stability: an example from New Mexico

M. J. Holdaway, J. W. Goodge

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18 Scopus citations

Abstract

A graphite-absent sequence of quartzite and schist on the north flank of the Picuris Range in north-central New Mexico provides a natural laboratory to test the thesis of Bruton and Helgeson that fluid pressure (Pf) is the effective pressure on solid phases during metamorphism. We have studied the Hondo Canyon and Section 8 areas of this range in detail. The presence of chloritoid + kyanite in the Ortega quartzite and staurolite in the adjacent Rinconada schists can best be explained by bulk compositional effects. A difference in Pf of 200 ± 100 bars between the two rock types can best be explained by a contrast of permeability between the quartzites and mica schists, because the preferred orientation of minerals and planar grain boundaries in the micaceous rocks favor greater and more rapid fluid flow. Pf builds up to values closer to lithostatic pressure in the quartzites than in the mica-rich rocks. In fluid-present systems during low- and medium-grade metamorphism generally, the effective pressure on solid minerals appears to be fluid pressure rather than rock pressure. -from Authors

Original languageEnglish (US)
Pages (from-to)1043-1058
Number of pages16
JournalAmerican Mineralogist
Volume75
Issue number9-10
StatePublished - Jan 1 1990

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