Abstract
The Tsukuba metamorphic area is underlain mostly by mica schists and gneisses derived from pelitic and psammitic sedimentary rocks of middle-late Triassic to late Jurassic. Three progressive zones A, B and C are classified on the basis of systematic variation of mineral parageneses. The representative assemblages of each zone are as follows.
A: muscovite+orthoclase+plagioclase+andalusite
B: fibrolite+muscovite+orthoclase+plagioclase+cordierite
C: fibrolite+orthoclase+plagioclase+cordierite+almandine
Biotite, quartz and graphite are found in almost all specimens studied. The geothermometry and geobarometry based on the dehydration reaction of muscovite and quartz, the polymorphic transition of Al2SiO5 minerals, the Fe-Mg partition between garnet and cordierite, and the two feldspar relation, enabled us to estimate the metamorphic con-ditions as 550° to 600°C, 3 to 4.5 Kb and 0.4-0.5 XH2O in the fluid phase.
