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Further observations related to a possible occurrence of terrestrial ahrensite

  • William E. Glassley EMAIL logo , John A. Korstgård und Kai Sørensen
Veröffentlicht/Copyright: 30. September 2016
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American Mineralogist
Aus der Zeitschrift American Mineralogist Band 101 Heft 10

Abstract

Clusters of aligned, highly elongate, prismatic quartz (Qtz) rods occur in a few fayalite (Fa) crystals in an eulysite from a recently identified ~1.8 Gy UHP site in central West Greenland (Glassley et al. 2014). Additional detailed analyses of the crystallography and phase compositions of these olivines were conducted to evaluate the postulate that the Qtz rods formed during inversion of super-silicic ahrensite to Fa+Qtz during decompression. These new observations show the Qtz rods consistently occur in crystallographically coherent clusters with the Qtz grains aligned parallel to [100] of Fa. The contrasting compositions of coexisting primary UHP Fa and Fa postulated to have formed by inversion of ahrensite are consistent with the inversion scenario. We thus conclude that all available data are consistent with the postulate that ahrensite was part of the equilibrium phase assemblage formed during UHP metamorphism and that it inverted to Fa+Qtz upon decompression. If true, this would represent the first occurrence of terrestrial ahrensite formed through natural tectonic processes.

Keywords: Ahrensite; UHP; quartz exsolution; fayalite; Greenland

Acknowledgments

We thank Jane Selverstone for useful comments on an earlier version of this document. We also thank Howard Day and Robert Zierenberg for resurrecting the universal stage. Reviews by W.L. Griffin, J.G. Liou, I.P. Swainson, and an anonymous reviewer greatly improved the manuscript and are gratefully acknowledged.

References cited

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Received: 2016-6-24
Accepted: 2016-7-14
Published Online: 2016-9-30
Published in Print: 2016-10-1

© 2016 by Walter de Gruyter Berlin/Boston

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https://doi.org/10.2138/am-2016-5899
Schlagwörter für diesen Artikel
Ahrensite; UHP; quartz exsolution; fayalite; Greenland

Artikel in diesem Heft

  1. Research Article
  2. Temporal histories of Cordilleran continental arcs: testing models for magmatic episodicity
  3. Chemistry and Mineralogy of Earth’s Mantle
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