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American Mineralogist

Journal of Earth and Planetary Materials

Ed. by Baker, Don / Xu, Hongwu / Swainson, Ian


IMPACT FACTOR 2018: 2.631

CiteScore 2018: 2.55

SCImago Journal Rank (SJR) 2018: 1.355
Source Normalized Impact per Paper (SNIP) 2018: 1.103

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1945-3027
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Volume 92, Issue 10

Issues

The relative stability of monazite and huttonite at 300 - 900 °C and 200 - 1000 MPa: Metasomatism and the propagation of metastable mineral phases

Daniel E. Harlov / Richard Wirth / Callum J. Hetherington
  • Department of Geosciences, University of Massachusetts, 611 North Pleasant Street, Amherst, Massachusetts 01003-9297, U.S.A.
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Published Online: 2015-04-01 | DOI: https://doi.org/10.2138/am.2007.2459

Abstract

Monazite is both partially replaced and overgrown by a ThSiO4 phase along grain rims in a series of experiments from 300 to 900 °C and 200 to 1000 MPa. All experiments consisted of 10 mg of 100.500 μm size, euhedral to subhedral crystals of a natural Th-free monazite-(Ce), 5 mg of Th(NO3)4·5H2O, 2.5 mg of SiO2, and 5 mg of H2O loaded into 3 mm wide, 1 or 1.3 cm long platinum capsules that were arc welded shut. Experimental conditions were: 300 °C at 200 and 500 MPa; 300, 400, 500, 600, and 700 °C at 500 MPa (cold seal hydrothermal autoclave); and 900 °C at 1000 MPa (Catz assembly; pistoncylinder press). Back-scattered electron (BSE) imaging, electron back-scattered diffraction (EBSD) analysis, and transmission electron microscopy (TEM) indicates that in the experiments from 500 to 900 °C, the ThSiO4 phase took the form of monoclinic huttonite implying that huttonite, associated with monazite, could exist metastably over a much greater P-T range than previously thought. TEM analysis of a foil cut perpendicular to the monazite-huttonite interface from the 600 °C, 500 MPa experiment using a focused ion beam (FIB) indicates that the huttonite as well as the interface between the huttonite and monazite is characterized by fluid inclusions. High-resolution TEM analysis indicates that the huttonite-monazite interface is coherent. In the case of replacement of monazite by huttonite, fluid-aided dissolution-reprecipitation is proposed as the most likely mechanism responsible.

Keywords: Monazite; huttonite; dissolution-reprecipitation; metastability; metasomatism; EBSD; TEM; pseudomorphism

About the article

Received: 2006-09-21

Accepted: 2007-06-05

Published Online: 2015-04-01

Published in Print: 2007-10-01


Citation Information: American Mineralogist, Volume 92, Issue 10, Pages 1652–1664, ISSN (Online) 1945-3027, ISSN (Print) 0003-004X, DOI: https://doi.org/10.2138/am.2007.2459.

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