Age and origin of fluorapatite-rich dyke from Baranec Mt. (Tatra Mts., Western Carpathians): a key to understanding of the post-orogenic processes and element mobility

Abstract

Abstract:On the southeastern slope of the Baranec Mount in the Western Tatra Mountains (Slovakia) an apatite-rich pegmatite-like segregation was found in the subvertical fault zone cutting metapelitic rocks. Two zones: felsic (F) and mafic (M) were found, differing in mineral assemblages and consequently in chemistry. Fluorapatite crystals yield a LA-ICP-MS U-Pb age of 328.6 ± 2.4 Ma. A temperature decrease from 634 °C to 454 °C at a pressure around 500 to 400 MPa with oxygen fugacity increasing during crystallization are the possible conditions for formation of the pegmatite-like segregation, while secondary alterations took place in the temperature range of 340 -320 °C. The Sr-Nd isotope composition of both apatite and whole rock point toward a crustal origin of the dike in question, suggesting partial melting of (P, F, H 2 O)-rich metasedimentary rocks during prolonged decompression of the Tatra Massif. The original partial melt (felsic component) was mixed with an external (F, H 2 O)-rich fluid, carrying Fe and Mg fluxed from more mafic metapelites and crystallizing as biotite and epidote in the mafic component of the dyke.

Variscan post-collisional cooling and uplift of the Tatra Mountains crystalline block constrained by integrated zircon, apatite and titanite LA-(MC)-ICP-MS U-Pb dating and rare earth element analyses

“…8c) that formed during a later thermal event. This is supported by late-Variscan hydrothermal processes involving (P, F, Ca, REE)-rich fluid migration which have recently been documented in the southern part of the metamorphic envelope and dated at 328 Ma (Gawęda et al, 2016c) and elsewhere in the crystalline cores of the Central Western Carpathians (Burda and Dzierżanowski, 2005;Ondrejka et al, 2012). Lastly, the youngest age-population in sample AMB-2, is comprised of grains with Ap2 and Ap3 trace element characteristics (Supplementary Table 3; Fig.…”

Acta Geologica Polonica

“…Apatite-rich cumulates, with apatite reaching 11-13 vol.%, were found both as an isolated enclave in granitoid (Gawęda 2008) and in situ (Szopa et al 2013). Apatite, together with plagioclase, K-feldspar, biotite and accessories (zircon, xenotime, monazite) is a cumulus phase.…”

“…unusual granitic apatite-rich cumulates (Szopa et al 2013). The High Tatra granite is characterised by an abundance of mafic enclaves and xenoliths of country rocks (Gawęda 2008;Gawęda and Szopa 2011) and offers a wide opportunity to study the magmas interaction. In all samples magmatic foliation and lineation are evident and indicate a top to the SE magma movement, concordant with the metamorphic foliation in the host rocks (Gawęda and Szopa 2011).…”

“…Thin sections for petrographical observations were cut perpendicularly to the magmatic foliation and parallel to the magmatic lineation, as shown by Gawęda and Szopa (2011) (Sun and McDonough 1995). For comparison we also used the published whole-rock analyses from Gawęda (2008).…”

“…Antecrysts and enclaves of older granite pulses are present elsewhere, especially inside the High Tatra granite (Gawęda 2008) and have been interpreted in terms of petrological cannibalism and magma recycling (Gawęda et al 2016).…”