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VARISCAN UPLIFT OF THE CRYSTALLINE BASEMENT, TATRA MTS., CENTRAL WESTERN CARPATHIANS: EVIDENCE FROM 40Ar/39Ar LASER PROBE DATING OF BIOTITE AND P-T-t PATHS

In: Geologica Carpathica, vol. 45, no. 5
Marian Janak

Details:

Year, pages: 1994, 293 - 300
About article:
The Variscan uplift between about 300–330 Ma has been documented for the crystalline basement in the Tatra Mts., Central Western Carpathians, on the basis of 40Ar/39Ar laser probe dating of biotite and reconstruction of P-T-t paths. The uplift history of two superimposed tectonic units-lower and upper, forming a Variscan nappe pile with inverted metamorphic zonation has been investigated. The upper structural unit composed of migmatized ortho- and paragneisses, amphibolites, calc-silicates and granitoids reveals two distinct stages of metamorphism, differing in pressure conditions. An earlier, high-pressure event M1 reached the temperature of about 700–800 °C at a pressure of 10–14 kbar, in the kyanite stability field, attaining conditions near the transition between amphibolite-granulite and eclogite facies. It is attributed to subduction (underthrusting) prior to Variscan uplift and exhumation. Subsequent low to intermediate pressure metamorphism M2 in the upper unit reached equilibria in the sillimanite stability field, at a temperature of about 650–750 °C and a pressure of 4–6 kbar. It is interpreted as a consequence of recrystallization during decompression and uplift, closely associated with the emplacement of granitoid pluton penetrating the upper unit. The lower unit, composed of mica schists, shows metamorphic zonation where mineral assemblages in metapelites and P-T conditions record increasing metamorphic grade from 570 °C to 640 °C at a pressure of 6–7 kbars. Metamorphic zonation in the lower unit is inferred to be a consequence of Variscan overthrusting and emplacement of the upper unit, being locally disturbed by Alpine tectonics. The reconstruction of metamorphic P-T-t paths yields generally ”clockwise” trajectories, characteristic for metamorphism due to crustal thickening. Late-Variscan uplift due to extension is proposed for the exhumation of the entire nappe pile, recorded by the blocking temperature for argon diffusion in the biotites. The 40Ar/39Ar data also suggest that Alpine tectono-thermal overprint was generally low, not exceeding the temperature of 300–350 °C.
How to cite:
ISO 690:
Janak, M. 1994. VARISCAN UPLIFT OF THE CRYSTALLINE BASEMENT, TATRA MTS., CENTRAL WESTERN CARPATHIANS: EVIDENCE FROM 40Ar/39Ar LASER PROBE DATING OF BIOTITE AND P-T-t PATHS. In Geologica Carpathica, vol. 45, no.5, pp. 293-300. 1335-0552.

APA:
Janak, M. (1994). VARISCAN UPLIFT OF THE CRYSTALLINE BASEMENT, TATRA MTS., CENTRAL WESTERN CARPATHIANS: EVIDENCE FROM 40Ar/39Ar LASER PROBE DATING OF BIOTITE AND P-T-t PATHS. Geologica Carpathica, 45(5), 293-300. 1335-0552.