Publication details
Alpine oxidation of lithium micas in Permian S-type granites (Gemeric unit, Western Carpathians, Slovakia)
| Authors | |
|---|---|
| Year of publication | 2014 |
| Type | Article in Periodical |
| Magazine / Source | Mineralogical Magazine |
| MU Faculty or unit | |
| Citation | |
| Web | http://minmag.geoscienceworld.org/content/78/3/507.abstract |
| Doi | http://dx.doi.org/10.1180/minmag.2014.078.3.03 |
| Field | Analytic chemistry |
| Keywords | lithium micas; zinnwaldite; phengite; Permian granite; oxidation; Alpine metamorphism; Gemeric unit; Western Carpathians; Slovakia |
| Description | Lithium micas of the zinnwaldite and phengite-Li-phengite series occur as characteristic minerals in Permian Li-F-(P) granites of the western Gemeric unit (Western Carpathians) accompanied by topaz, tourmaline, Nb, Ta, Ti, Sn oxides and aluminophosphates. The calculated Li2O contents of all the mica analysed, together with Rb2O and Cs2O were confirmed by LA-ICP-MS analyses for all the identified micas. Samples from three localities were investigated: two surficial (Surovec, Vrchsul'ova); and one drill hole (Dlha dolina). Zinnwaldite (polylithionite) occurs in the upper level of the Dlha dolina granitic intrusion and in the nearby shallow satellite body of Surovec. The lower level porphyritic granites contain only siderophyllite. The Vrchsul'ova micas are closer in composition to Li-annite and siderophyllite. Dioctahedral micas are mostly phengites, although zinnwaldite-bearing granites are rich in late-crystallizing Li-phengite, which extensively replaces earlier zinnwaldite. The secondary Li-phengite and phengite are interpreted as products of Alpine metamorphism during Cretaceous burial and subsequent exhumation of the Gemeric unit. Reactions are suggested explaining the formation of Li-phengite by reaction of zinnwaldite with phengite or with muscovite. All mica types were investigated by Mossbauer spectroscopy, which showed high degrees of oxidation (25-50% Fe3+ of total Fe) with the exception of zinnwaldite from Vrchsul'ova, which may have preserved an original, reduced value of 10%. The metamorphic assemblage present permitted calculation of P-T-X conditions: T = 184 degrees C, P = 320 MPa, with oxidation of siderophyllite to phengite + goethite and f(O2) at Delta NN = 4.7, confirming the low-grade conditions of the Alpine metamorphism in agreement with previous estimates. |