PETROLOGY AND GEOLOGICAL SIGNIFICANCE OF HIGH-PRESSURE METAMORPHIC ROCKS OCCURRING AS PEBBLES IN THE CRETACEOUS CONGLOMERATES OF THE KLIPPEN BELT (WESTERN CARPATHIANS, SLOVAKIA)

In the absence of requisite outcrops, pebbles of critical rock types i n younger sedimentary sequences contribute important and otherwise uno btainable information on the geodynamics of orogenic belts. In this re spect, high-pressure metabasites occurring as pebbles in the Albian co nglomerates near Povazska Bystrica (Central Slovakia) yield new data o n the subduction history of parts of the Western Carpathians. They com prise three different types ranging from pumpellyite- through lawsonit e- to omphacite-bearing blueschists. In addition to blue amphiboles (g laucophane, ferro-glaucophane and winchite), these blueschist pebbles also contain minor amounts of phengite, chlorite, albite and quartz. C rossite-riebeckite and aegirine are present in ferruginous quartzite p ebbles. The jadeite component in omphacite ranges from 38 to 60 mol%. Si content of phengite corresponds to 3.45-3.5 atoms per formula unit based on 11 anhydrous oxygens. The estimated temperatures and pressure s are 310-360 degrees C at 7-9.5 kbar for pumpellyite-, 325-375 degree s C at 9-11.5 kbar for lawsonite- and 360-420 degrees C at 10.5-12.5 k bar. for the omphacite-bearing blueschists. These P-T conditions indic ate a subduction regime of pre-Albian age probably formerly located in a relatively external portion of the Western Carpathians with a mean linear geotherm of about 9-10 degrees C/km.