| Abstract: | Crystals of zircon up to 3 mm in length occur in jadeitite veins in the Osayama serpentinite me??lange, Southwest Japan. The zircon porphyroblasts show pronounced zoning, and are characterized by both low Th/U ratios (0.2-0.8) and low Th and U abundances (Th = 1-81 ppm; U = 6-149 ppm). They contain inclusions of high-pressure minerals, including jadeite and rutile; such an occurrence indicates that the zircon crystallized during subduction-zone metamorphism. Phase equilibria and the existing fluid-inclusion data constrain P-T conditions to P> 1.2 GPa at T < 350??C for formation of the jadeitite. Most U/Pb ages obtained by SHRIMP-RG are concordant, with a weighted mean 206Pb/238U age of 472 ?? 8.5 Ma (MSWD = 2.7, n = 25). Because zircon porphyroblasts contain inclusions of high-pressure minerals, the SHRIMP U-Pb age represents the timing of jadeitite formation, i.e., the timing of interaction between alkaline fluid and ultramafic rocks in a subduction zone. Although this dating does not provide a direct time constraint for serpentinization, U-Pb ages of zircon in jadeitite associated with serpentinite result in new insights into the timing of fluid-rock interaction of ultramafic rocks at a subduction zone and the minimum age for serpentinization. Copyright ?? 2005 by V.H. Winston & Son, Inc. All rights reserved. |
| Genre: | Article |
| ProdID: | 70027883 |
| Citation Author: | Tsujimori, T.; Liou, J. G.; Wooden, J.; Miyamoto, T. |
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| Citation End Page: | 1057 |
| Citation Issue: | 10 |
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| Citation Language: | English |
| Citation Larger Work Title: | International Geology Review |
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| Citation Number Of Pages: | 10 |
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| Citation Search Results Text: | U-Pb dating of large zircons in low-temperature jadeitite from the Osayama serpentinite me??lange, Southwest Japan: Insights into the timing of serpentinization; 2005; Article; Journal; International Geology Review; Tsujimori, T.; Liou, J. G.; Wooden, J.; Miyamoto, T. |
| Citation Start Page: | 1048 |
| Citation Volume: | 47 |
| Citation Year: | 2005 |
| Type: | citation/reference |
| Text: | U-Pb dating of large zircons in low-temperature jadeitite from the Osayama serpentinite me??lange, Southwest Japan: Insights into the timing of serpentinization; 2005; Article; Journal; International Geology Review; Tsujimori, T.; Liou, J. G.; Wooden, J.; Miyamoto, T. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| Date Other: | Sat, 1 Jan 2005 00:00 -0600 |
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