科研之友
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摘要
Three quartzitic metapelites with garnet-chloritoid-kyanite assemblage from the Eclogite Zone, Tauern Window, Austria have been studied based on pseudosections in the KNCFMMnASTH and partly KNCFMMnASTHO system compared with measured and calculated garnet zonations along three P-T paths. Deduced garnet core growth is in the range 502-521 degrees C, 20.2-21.4 kbar, corresponding to overstepping the garnet-in reaction by similar to 25-100 degrees C for P-T paths 1, 2 and similar to 72-133 degrees C for P-T path 3. The peak assemblage garnet-chloritoid-kyanite-phengite-paragonite-rutile-quartz in sample A is stable in a narrow maximum similar to 10 degrees C band from similar to 598 degrees C/14 kbar to similar to 570 degrees C/24.9 kbar. In sample B and C this stability is much more restricted with similar to 2 degrees C width from similar to 581 degrees C/22.3 kbar to similar to 572 degrees C/24.5 kbar and similar to 4 degrees C/0.7 kbar width at similar to 570 degrees C/24.8 kbar. Temperature differences between measured and calculated pyrope and grossular isopleths are generally in the range from 0 to 20 degrees C, however larger values are sometimes obtained. The proposed P-T paths reach peak values around 570-575 degrees C/24.6 kbar. Comparison of measured and calculated garnet zonation suggests a better accordance for unfractionated than for fractionated models. Several factors could be responsible for this and the partly large overstepping values, e. g. insufficient thermodynamic data, or non-equilibrium reactions due to sluggish nucleation or breakdown reactions and later garnet re-equilibration.
- 出版日期2013-8
