GEOLOGIC THERMOBAROMETRY OF RETROGRADED METAMORPHIC ROCKS: AN INDICATION OF THE UPLIFT TRAJECTORY OF A PORTION OF THE NORTHERN SCANDINAVIAN CALEDONIDES.

Kyanite grade pelitic schists from the Efjord area (68 degree 15 prime N, 16 degree 45 prime E), northern Norway, show abundant textural evidence of retrograde reequilibration during late orogenic uplift and cooling of this part of the Scandinavian Caledonides. Graphical analysis of mineral compositions in seven samples that show a range of retrograde textures indicates that they reached final chemical equilibrium under nonuniform pressure-temperature conditions. Three element-partitioning geothermometers and geobarometers yield consistent PT estimates in individual samples, which together define a trend in PT space. The sample showing the fewest signs of retrogression yields the highest pressure and temperature estimates, whereas samples exhibiting abundant reequilibration textures give lower PT estimates. It is suggested that the trend indicated by these samples reflects a portion of the PT trajectory assumed by the Efjord area during uplift.