Fate of the subducted Farallon plate inferred from eclogite xenoliths in the Colorado Plateau
- 1Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Study of the Earth's Interior, Okayama University at Misasa, Tottori 682-0193, Japan
- 2Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan
- 3Department of Geological Sciences and Geological Engineering, Queen's University, Kingston, Ontario K7L 3N6, Canada
Abstract
We present the first finding of the high-pressure mineral coesite in lawsonite-bearing eclogite xenoliths from the Colorado Plateau, United States. The presence of coesite in these xenoliths supports the hypothesis that the eclogite formed in a low-temperature–high-pressure environment such as envisaged inside subducted oceanic lithosphere. Ion-microprobe U-Pb dating of micrometer-scale zircons in the eclogites yields ages ranging from 81 Ma to 33 Ma, the two extremes in age likely indicating the age of crystallization during subduction-related metamorphism and the age of recrystallization by the host magmatic event, respectively. These observations conclusively demonstrate that certain eclogite xenoliths from the Colorado Plateau originated as fragments of the subducted Farallon plate, which had been residing in the upper mantle since the Late Cretaceous. This is the first conclusive evidence that any eclogite xenoliths can be directly linked to a known subducted plate.
Footnotes
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↵GSA Data Repository item 2003085, Tables DR1–DR4, whole-rock major element and representative mineral compositions in eclogite xenoliths, is available on request from Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301-9140, USA, editinggeosociety.org, or at http://www.geosociety.org/pubs/ft2003.htm.
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- Accepted April 7, 2003.
- Received January 6, 2003.
- Revision received April 4, 2003.
- Geological Society of America
