Petrology and geological significance of high-pressure metamorphic rocks occurring as pebbles in the Cretaceous conglomerates of the Klippen Belt (Western Carpathians, Slovakia)

Pebbles of high-P metabasic rocks found in the Albian conglomerates near Povazska Bystrica, central Slovakia, comprise three different types, ranging from pumpellyite- to lawsonite- to omphacite-bearing blueschists. In addition to the blue amphiboles glaucophane, ferroglaucophane and winchite, these blueschist pebbles also contain minor amounts of phengite, chlorite, albite and quartz; ferroglaucophane-riebeckite and aegirine are present in ferruginous quartzite pebbles. Representative EPMA results are reported for the amphiboles, pumpellyite, lawsonite, epidote, phengite, sodic pyroxenes and chlorite. The jadeite component in omphacite ranges from 38 to 60 mol.%; Si content of phengite corresponds with 3.45-3.5 atoms pfu based on 11 anhydrous oxygens. The estimated P-T conditions are 310-360 degrees C/7-9.5 kbar for pumpellyite-, 325-375 degrees C/9-11.5 kbar for lawsonite- and 360-420 degrees C/10.5-12.5 kbar for the omphacite-bearing blueschists. These P-T conditions indicate a subduction regime of pre-Albian age probably located in a relatively external part of the W Carpathians with a mean linear geotherm of approximately 9-10 degrees C/km.