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Science 14 April 2000:
Vol. 288. no. 5464, pp. 321 - 324
DOI: 10.1126/science.288.5464.321
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Reports

Nanometer-Size alpha -PbO2-Type TiO2 in Garnet: A Thermobarometer for Ultrahigh-Pressure Metamorphism

Shyh-Lung Hwang, 1 Pouyan Shen, 2* Hao-Tsu Chu, 3 Tzen-Fu Yui 4

A high-pressure phase of titanium dioxide (TiO2) with an alpha -PbO2-type structure has been identified in garnet of diamondiferous quartzofeldspathic rocks from the Saxonian Erzgebirge, Germany. Analytical electron microscopy indicates that this alpha -PbO2-type TiO2 occurred as an epitaxial nanometer-thick slab between twinned rutile bicrystals. Given a V-shaped curve for the equilibrium phase boundary of alpha -PbO2-type TiO2 to rutile, the stabilization pressure of alpha -PbO2-type TiO2 should be 4 to 5 gigapascals at 900° to 1000°C. This suggests a burial of continental crustal rocks to depths of at least 130 kilometers. The alpha -PbO2-type TiO2 may be a useful pressure and temperature indicator in the diamond stability field.

1 Department of Materials Science and Engineering, I-Shou University, Kaohsiung, Taiwan, ROC.
2 Institute of Materials Science and Engineering, National Sun Yat-sen University, Kaohsiung, Taiwan, ROC.
3 Central Geological Survey, Post Office Box 968, Taipei, Taiwan, ROC.
4 Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan, ROC
*   To whom correspondence should be addressed. E-mail: pshen{at}mail.nsysu.edu.tw

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