A new determination of the alpha-beta quartz boundary based on the equation of state of H[sub 2]O and laser interferometry in a diamond-anvil cell
- Cornell Univ., Ithaca, NY (United States). Dept. of Geological Sciences
- Geological Survey, Reston, VA (United States). National Center
The [alpha]-[beta] quartz boundary has been re-determined in a diamond anvil cell by using (1) laser interferometry to observe the transition and (2) the equation of state of H[sub 2]O to calculate transition pressures (P[sub tr]) at five measured transition temperatures (T[sub tr]; up to 852 C). The sample chamber, formed by compressing a 125[mu]m-thick rhenium gasket (with a 500[mu]m-diameter hole) between two diamond anvils, was loaded with a doubly-polished quartz platelet (with its c-axis perpendicular to the polished surfaces), distilled-deionized water, and an air bubble. The laser light reflected from the top and bottom surfaces of quartz produces interference fringes. Both [alpha] to [beta] and [beta] to [alpha] transitions manifest themselves as collective abrupt motions in the interference fringes resulting from the sudden changes in the refractive indices. After each determination of T[sub tr], the sample was cooled nearly isochorically (less than 0.5% variation in volume), and the density of the fluid medium was obtained from the measured homogenization temperature (accurate to [+-] 0.5 C). P[sub tr] was then calculated from T[sub tr] and the density data by using the equation of state of H[sub 2]O. A least-squares fit of the authors data and the 1 atmosphere datum (573 C) yields T[sub tr](C) = 574.3 + 0.2559 P[sub tr] (MP[sub a]) [minus] 6.406 [times] 10[sup [minus]6]P[sub tr]w. This formulation is in excellent agreement with the results of Coe and Paterson at pressures below 500 MPa, and with Mirwald and Massonne at higher pressures. Furthermore, the extrapolation of their equation almost exactly passes through the [alpha]-quartz, [beta]-quartz, and coesite triple point reported by Mirwald and Massonne at 1,380 [+-] 15 C and 3,440 [+-] 20MPa.
- OSTI ID:
- 5807930
- Report Number(s):
- CONF-921058-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 24:7; Conference: 1992 annual meeting of the Geological Society of America (GSA), Cincinnati, OH (United States), 26-29 Oct 1992; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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