look inside of diamond-forming media in deep subduction zones

Geologists have "known" for many years that continental crust is buoyant and cannot be subducted very deep. Microdiamonds 10-80 μm in size discovered in the 1980s within metamorphic rocks related to continental collisions clearly refute this statement, suggesting that material of continent...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2007-05, Vol.104 (22), p.9128-9132
Main Authors: Dobrzhinetskaya, Larissa F, Wirth, Richard, Green, Harry W. II
Format: Article
Language:English
Subjects:
08 HYDROGEN
CARBON
CONTINENTAL CRUST
CRYSTALLIZATION
Crystallography
Crystals
DIAMONDS
Fluids
Garnets
Geology
High-Pressure Geoscience Special Feature
HYDROGEN
Inclusions
Infrared radiation
ION BEAMS
Mass spectrometry
MASS SPECTROSCOPY
METAMORPHIC ROCKS
Mineralogy
Minerals
MOUNTAINS
national synchrotron light source
Nitrogen
OXYGEN
PARTICLE ACCELERATORS
Petrology
Physical Sciences
Rocks
Scanning electron microscopy
SPECTROSCOPY
STABLE ISOTOPES
SUBDUCTION ZONES
SYNCHROTRON RADIATION
Synchrotrons
TECTONICS
TRANSMISSION ELECTRON MICROSCOPY
WATER
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Summary:Geologists have "known" for many years that continental crust is buoyant and cannot be subducted very deep. Microdiamonds 10-80 μm in size discovered in the 1980s within metamorphic rocks related to continental collisions clearly refute this statement, suggesting that material of continental crust has been subducted to a minimum depth of >150 km and incorporated into mountain chains during tectonic exhumation. Over the past decade, the rapidly moving technological advancement has made it possible to examine these diamonds in detail, and to learn that they contain nanometric multiphase inclusions of crystalline and fluid phases and are characterized by a "crustal" signature of carbon stable isotopes. Scanning and transmission electron microscopy, focused ion beam techniques, synchrotron infrared spectroscopy, and nano-secondary ion mass spectrometry studies of these diamonds provide evidence that they were crystallized from a supercritical carbon-oxygen-hydrogen fluid. These microdiamonds preserve evidence of the pathway by which carbon and water can be subducted to mantle depths and returned back to the earth's surface.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.0609161104