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  • Author or Editor: Shah Wali Faryad x
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K-Ar age data from minerals (white mica, amphibole, biotite, and feldspar) in metamorphic rocks and pegmatite indicate Variscan metamorphic and magmatic events in the Zemplin Unit. The rocks hosting these minerals are amphibolite, gneiss, micaschist, and pegmatite. This is the first report on the occurrence of pegmatite from this unit, which indicates a Variscan age (≯ 307.9 ± 12.0 Ma) for igneous activity. Amphibolite facies metamorphism is dated based on K-Ar measurement of amphibole from amphibolite that gave age of 338 Ma. K-Ar ages of muscovite and of some amphiboles depend on the degree of mylonitization of the host micaschists and amphibolite, and range from 284.8 ± Ma to 211 ± 9 Ma. Ar/Ar spectrum on a white mica of 227 Ma K-Ar age yielded a ca. 300 Ma plateau-like age and indicates a younger, most likely Alpine overprint. Cretaceous ages of 105 ± 4.2 Ma and 126.6 ± 5.2 Ma were obtained from plagioclase and from white mica concentrate (< 2µm fraction) from strongly mylonitized amphibolite. This suggests that most K/Ar ages between the Variscan and Alpine orogenies (284-211 Ma) are geologically meaningless mixed values. The data support the interpretation of Variscan amphibolite facies metamorphism ≯ 338 Ma with subsequent magmatism ≯ 307.9 Ma) followed by Alpine overprint (126-105 Ma).

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