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Published December 1968 | public
Journal Article

O¹⁸/O¹⁶ Ratios of Coexisting Minerals in Glaucophane-Bearing Metamorphic Rocks

Abstract

Oxygen isotope analyses have been obtained for coexisting minerals in several blue-schist-facies metamorphic rocks from California, Oregon, and New Caledonia. Detailed isotopic studies were made on a continuous exposure of schist in Ward Creek, California, previously described by Coleman and Lee (1962). The oxygen isotope fractionations among coexisting minerals in a variety of rock types, including metasediments and metabasalts, are systematic and larger than those measured in pelitic schists metamorphosed at the grade of biotite zone or higher. Therefore, these Ward Creek rocks (termed Type III) must have formed at lower temperatures than have such pelitic schists. Evidence for significant isotopic equilibration and homogenization is observed in the Ward Creek sequence. Six different metasediments and metavolcanics collected within 25 m of one another show almost identical mineral δ;-values: quartz (15.8 to 16.3), aragonite (13.1 to 13.3), glaucophane (9.8 to 10.0), muscovite (10.9 to 11.3), lawsonite (9.3 to 9.5), and garnet (8.0 to 8.4), given as per mil enrichment in O18 relative to mean ocean water. These rocks seem to have reached equilibrium at about the same temperature in contact with abundant metamorphic pore fluids.

Additional Information

We wish to thank Paul Yanagisawa for performing many of the fluorine extractions of oxygen from minerals, and Terry Keith for numerous mineral separations. Financial port for this research was provided by the National Science Foundation, Grant No. GA-513, and by the Alfred P. Sloan Foundation. We are indebted to Prof. W. G. Ernst, University of California at Los Angeles, for a critical reading of the manuscript. Prof. R. N. Brothers, University of Auckland, has been helpful in adding to our knowledge on the New Caledonian glaucophane schist areas, and Dr. M. C. Blake, Jr., U.S. Geological Survey, provided us with samples and mineral separates from the Yolla Bolly area, California.

Additional details

Created:
August 21, 2023
Modified:
October 24, 2023