The OH content of pyrope at high pressure

The OH contents of pyrope garnets synthesised at 1000°C and pressures between 2 and 13 GPa have been measured by infrared spectroscopy. We find that under the same conditions of pressure, temperature, a H 2O and a SiO 2 the OH content of pyrope is similar to that of grossular. This shows that observ...

Full description

Saved in:
Bibliographic Details
Published in:Chemical geology 1998-05, Vol.147 (1), p.161-171
Main Authors: Withers, Anthony C., Wood, Bernard J., Carroll, Michael R.
Format: Article
Language:English
Subjects:
Hydroxyl ion
Infrared spectroscopy
Mantle
Pressure
Pyrope
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:The OH contents of pyrope garnets synthesised at 1000°C and pressures between 2 and 13 GPa have been measured by infrared spectroscopy. We find that under the same conditions of pressure, temperature, a H 2O and a SiO 2 the OH content of pyrope is similar to that of grossular. This shows that observed differences in nature between water contents of pyrope and grossular are related to paragenesis rather than reflecting higher intrinsic solubility in grossular. In the presence of excess SiO 2 the H 2O content increases with pressure to 5 GPa (1000 ppm) then decreases to below the detection limit at pressures above 7 GPa. Thus garnet becomes more hydrous with pressure to some critical value, beyond which dehydration occurs even under H 2O-saturated conditions. This observation is consistent with the measured partial molar volume of water in hydrogarnet which becomes greater than that in fluid water within the pressure range of this study. When corrected to upper mantle conditions we find that pyrope should dehydrate with increasing depth below about 250 km. Pyrope is unlikely therefore to be a major site of water storage in the transition zone and upper mantle.
ISSN:0009-2541
1872-6836
DOI:10.1016/S0009-2541(97)00179-4