Experimental determination of the reaction aragonite plus magnesite = dolomite at 5 to 9 GPa

被引:100
作者
Luth, RW [1 ]
机构
[1] Univ Alberta, Dept Earth & Atmospher Sci, CM Scarfe Lab Expt Petrol, Edmonton, AB T6G 2E3, Canada
基金
加拿大自然科学与工程研究理事会;
关键词
D O I
10.1007/s004100100238
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
Martinet et al, bracketed the decomposition reaction of dolomite to aragonite + magnesite between 5.0 and 5.5 GPa at 600 OC using in-situ XRD in a multianvil apparatus. They then extrapolated their results using the available thermodynamic data such that the breakdown reaction occurs at similar to1,000 degreesC at 6 GPa. If correct, this extrapolation has implications for the type(s) of stable carbonate(s) in the mantle. For example, the reaction magnesite + diopside = dolomite + enstatite would be metastable at P > 7 GPa relative to the aragonite-containing analog, and thus aragonite, rather than dolomite, might be stable near the solidus of Iherzolite. This extrapolation would also imply that aragonite and magnesite would be stable in garnet + clinopyroxene assemblages at pressures in the stability field of diamond. To test this extrapolation, experiments were conducted at higher temperatures in a multiple-anvil apparatus. Results of initial experiments were consistent with the results of Martinet et al. At higher temperatures, however, the reaction occurs at higher pressures than predicted by Martinet et al., requiring significant curvature to the reaction boundary. This curvature (increasing dP/dT with increasing T) is consistent with increasing disorder in the dolomite with increasing temperature, increasing the stability of dolomite relative to aragonite plus magnesite. The experimental results restrict aragonite + magnesite-bearing assemblages to low temperature. Aragonite will not be present in near-solidus Iherzolite, and can be present in orthopyroxene-free eclogites and pyroxenites only at low temperature.
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页码:222 / 232
页数:11
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