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American Mineralogist

Journal of Earth and Planetary Materials

Ed. by Putirka, Keith / Swainson, Ian

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1945-3027
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Volume 91, Issue 7

Issues

The origin of jadeitite-forming subduction-zone fluids: CL-guided SIMS oxygen-isotope and trace-element evidence

Sorena Sorensen
  • Corresponding author
  • Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560-0119, U.S.A.
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/ George E. Harlow
  • Department of Earth and Planetary Sciences, American Museum of Natural History, Central Park West at 79th St., New York, New York 10024, U.S.A.
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/ Douglas Rumble III
  • Geophysical Laboratory, Carnegie Institution of Washington, 5541 Broad Branch Road NW, Washington, D.C. 20015, U.S.A.
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Published Online: 2015-03-31 | DOI: https://doi.org/10.2138/am.2006.1949

Abstract

Jadeitite, a rare high P/T rock, is associated spatially with blueschist and/or eclogite terranes. Scanning electron microscope (SEM) and cathodoluminescence (CL) petrography of jadeitite samples from several major occurrences [in Burma (Myanmar), Guatemala, Japan, Kazakhstan, and the U.S.A.] show that grains were deposited from fluids. Jadeite grain compositions indicate these fluid compositions changed with time.

CL imagery guided the acquisition of oxygen-isotope and trace-element analyses with the ion microprobe. Jadeite grains in each rock grew in cycles that began with red- and/or blue-luminescent and ended with green-luminescent zones. The CL images were used to order the data into crystallization sequences. These data and electron-microprobe, major-element analyses document the association of green CL with increases in Ca, Mg, and Cr: (1) toward grain exteriors; (2) in fine-grained matrix around porphyroblasts; (3) in shear zones that cut grains; (4) in former open spaces now filled with jadeite; or (5) in veins. Abundances of many trace elements are greater in green-CL jadeitite compared with the red- or blue-CL zones. Some of these elements.in particular Li, Rb, Sr, Ti, Hf, Zr, Y, and REE.are unlikely to have been derived from serpentinite. Although crystal-chemical effects may explain some of the trace-element systematics (e.g., preferential incorporation of REE into Ca-richer jadeite), some kinetic control is suggested by sector-zoned, rhythmically zoned grains. The oxygen-isotope data suggest that jadeitite-depositing fluids either had multiple sources or evolved in composition along their flow paths (or both).

Keywords : Gems and gemstones; metamorphic petrology; analysis; chemical; major and minor elements; trace elements and REE; stable isotopes; petrography

About the article

Received: 2005-03-23

Accepted: 2006-02-03

Published Online: 2015-03-31

Published in Print: 2006-07-01


Citation Information: American Mineralogist, Volume 91, Issue 7, Pages 979–996, ISSN (Online) 1945-3027, ISSN (Print) 0003-004X, DOI: https://doi.org/10.2138/am.2006.1949.

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