Granitic pegmatites of the Western Carpathians: a reviewArticle PDF
Granitic pegmatites of the Western Carpathians: a review
The West-Carpathian granitic pegmatites form dikes to lensoid bodies (<10 m thick) in parental, orogenrelated Variscan calc-alkaline granitic rocks (tonalites, granodiorites and granites) of S- and I-type affinity or in adjacent Paleozoic metamorphic rocks of the amphibolite facies (mainly micaschists, paragneisses, locally orthogneisses, amphibolites and marbles). The pegmatites show zoning with aplite, coarse-grained, graphic to blocky K-feldspar and quartz units (commonly from rims to central parts), as well as quartzmuscovite and saccharoidal albite to cleavelandite replacement units. K-feldspar (microcline > orthoclase), albite, quartz and muscovite (± biotite) are the main rock-forming minerals. The most widespread accessory minerals comprise almandine to spessartine, Hf-rich zircon and fluorapatite, less common are schorl, gahnite, monazite-(Ce), xenotime-(Y), molybdenite, uraninite and other minerals. The most fractionated pegmatites include rare-element minerals: beryl (with secondary phenakite + bertrandite) and Nb-Ta oxide phases, mainly columbite-(Fe) to tantalite-(Mn), rarely tapiolite-(Fe), ferrowodginite, and secondary pyrochlore to microlite. Dating of the pegmatites (U–Th–Pb, Sm–Nd, Re–Os, Rb–Sr, Ar–Ar methods) reveal their Variscan (Late Devonian to Lower Carboniferous) age of ~360 to 330 Ma, locally with younger overprint during 220–315 Ma. The West-Carpathian granitic pegmatites are usually relatively primitive and they belong to the barren, muscovite class, however the most fractionated bodies show affinity to berylcolumbite subtype of rare-element class and LCT family. Close relations to granites indicate magmatic fractionation as the most important genetic model of the pegmatite origin, although partial anatexis of metapelite protolith is an alternative scenario for some West-Carpathian pegmatites. The primary magmatic stage (~740 to 500 °C) was followed by post-magmatic (mainly hydrothermal) stage (~400 to 250 °C), including local Alpine tectonic oveprint of the pegmatites. The West-Carpathian Variscan granitic pegmatites form an independent province, poor in Li a B, in contrast to pegmatites of adjacent pre-Alpine terranes (Bohemian Massif, Eastern Alps, Eastern and South Carpathians).
Pavel Uher, Dept. of Mineralogy and Petrology, Faculty of Natural Sci., Comenius University, Ilkovičova 6, 842 15 Bratislava, Slovak Republic; email@example.com