Rare-element granitic pegmatite of Miocene age emplaced in UHP rocks from Visole, Pohorje Mountains (Eastern Alps, Slovenia): accessory minerals, monazite and uraninite chemical dating

Abstract

Abstract:The granitic pegmatite dike intruded the Cretaceous UHP rocks at Visole, near Slovenska Bistrica, in the Pohorje Mountains (Slovenia). The rock consists mainly of K-feldspar, albite and quartz, subordinate muscovite and biotite, while the accessory minerals include spessartine-almandine, zircon, ferrocolumbite, fluorapatite, monazite-(Ce), uraninite, and magnetite. Compositions of garnet (Sps [48][49] Alm [45][46] Grs +And 3-4 Prp 1.5-2 ), metamict zircon with 3.5 to 7.8 wt. % HfO 2 [atom. 100Hf/(Hf + Zr) = 3.3-7.7] and ferrocolumbite [atom. Mn/(Mn + Fe) = 0.27-0.43, Ta/(Ta + Nb) = 0.03-0.46] indicate a relatively low to medium degree of magmatic fractionation, characteristic of the muscovite -rare-element class or beryl-columbite subtype of the rare-element class pegmatites. Monazite-(Ce) reveals elevated Th and U contents ( ≤ 11 wt. % ThO 2 , ≤ 5 wt. % UO 2 ). The monazite-garnet geothermometer shows a possible precipitation temperature of ~495 ± 30 °C at P~4 to 5 kbar. Chemical U-Th-Pb dating of the monazite yielded a Miocene age (17.2 ± 1.8 Ma), whereas uraninite gave a younger (~14 Ma) age. These ages are comtemporaneous with the main crystallization and emplacement of the Pohorje pluton and adjacent volcanic rocks (20 to 15 Ma), providing the first documented evidence of Neogene granitic pegmatites in the Eastern Alps. Consequently, the Visole pegmatite belongs to the youngest rare-element granitic pegmatite populations in Europe, together with the Paleogene pegmatite occurrences along the Periadriatic (Insubric) Fault System in the Alps and in the Rhodope Massif, as well as the Late Miocene to Pliocene pegmatites in the Tuscany magmatic province (mainly on the Island of Elba).

Metapelite from the high‐ to ultrahigh‐pressure terrane of the Eastern Alps (Pohorje Mountains, Slovenia)—New pressure, temperature and time constraints on a polymetamorphic rock

“…These ages fit with Sm-Nd garnet ages of eclogite , gneiss F I G U R E 1 (a) Tectonic map according to Ratschbacher et al (1989) showing the main units of the Central and Eastern Alps with (b) a more detailed map after Uher et al (2014) and Sandmann et al (2016). (c) Geological map of the southeastern Pohorje (with sample location) after Kirst et al (2010) and Uher et al (2014) [Colour figure can be viewed at wileyonlinelibrary.com] T A B L E 1 The bulk-rock composition (wt%) of the studied micaschist was determined with an X-ray fluorescence (XRF) spectrometer. XRFA is the bulk-rock composition after subtracting 2.5 wt% FeO from the original composition.…”

“…The timing of metamorphism in the Pohorje nappe is generally accepted to be Eo-Alpine (Sandmann et al, 2016 precise metamorphic ages have been summarized in recent literature (De Hoog et al, 2009;Hauzenberger et al, 2016;Janák et al, 2006Janák et al, , 2015Sandmann et al, 2016): U-Pb zircon ages of eclogite and metapelite are c. 93-90 Ma (Janák et al, 2009;. These ages fit with Sm-Nd garnet ages of eclogite , gneiss F I G U R E 1 (a) Tectonic map according to Ratschbacher et al (1989) showing the main units of the Central and Eastern Alps with (b) a more detailed map after Uher et al (2014) and Sandmann et al (2016). (c) Geological map of the southeastern Pohorje (with sample location) after Kirst et al (2010) and Uher et al (2014) [Colour figure can be viewed at wileyonlinelibrary.com] T A B L E 1 The bulk-rock composition (wt%) of the studied micaschist was determined with an X-ray fluorescence (XRF) spectrometer.…”

Diamond in metasedimentary crustal rocks from Pohorje, Eastern Alps: a window to deep continental subduction

“…The metamorphic rocks are intruded by a granodioritic to tonalitic pluton and pegmatites of Miocene age ( c . 20–15 Ma; Altherr et al ., ; Fodor et al ., ; Trajanova et al ., ; Uher et al ., ). The Late Cretaceous age of eclogite facies metamorphism in the Pohorje nappe is documented by garnet Sm–Nd and zircon U–Pb on eclogites ( c .…”

REE-bearing minerals in Drava river sediments, Slovenia, and their potential origin

“…(uHeR et al, 2014). In the work of FinGeR et al (1998), samples of monazite were acquired from Granatspitz massif in Tauern Window, from S-type granite gneiss metamorphosed to amphibolite facies.…”