Petrology and geological significance of high-pressure metamorphic rocks occurring as pebbles in the Cretaceous conglomerates of the Klippen Belt (Western Carpathians, Slovakia)
Faryad, Shah Wali; Schreyer, Werner
European Journal of Mineralogy Volume 9 Number 3 (1997), p. 547 - 562
published: Jun 2, 1997
manuscript accepted: Dec 13, 1996
manuscript received: May 26, 1995
ArtNo. ESP147050903016, Price: 29.00 €
Abstract Inthe absence of requisite outcrops, pebbles of critical rock types in younger sedimentary sequences contribute important and otherwise unobtainable information on the geodynamics of orogenic belts. In this respect, high-pressure metabasites occurring as pebbles in the Albian conglomerates near Povazská Bystrica (Central Slovakia) yield new data on the subduction history of parts of the Western Carpathians. They comprise three different types ranging from pumpellyite- through lawsonite- to omphacite-bearing blueschists. In addition to blue amphiboles (glaucophane, ferro-glaucophane and winchite), these blueschist pebbles also contain minor amounts of phengite, chlorite, albite and quartz. Crossite-riebeckite and aegirine are present in ferruginous quartzite pebbles. 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 pressures are 310-360 °C at 7-9.5 kbar for pumpellyite-, 325-375 °C at 9-11.5 kbar for lawsonite- and 360-420 °C at 10.5-12.5 kbar for the omphacite-bearing blueschists. These P-T conditions indicate 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 °C/km.