Monazite Th-U-total Pb geochronology and P-T thermodynamic modelling in a revision of the HP-HT metamorphic record in granulites from Stary Gierałtów (NE Orlica-Śnieżnik Dome, SW Poland)

Abstract

1 In sti tute of Geo log i cal Sci ences, Pol ish Acad emy of Sci ences, Re search Cen tre in Kraków, Senacka 1, 31-002 Kraków, Po land 2 In sti tute of Geo log i cal Sci ences, Pol ish Acad emy of Sci ences, Re search Cen tre in Wroc³aw, Podwale 75, 50-449 Wroc³aw, Po land 3 AGH Uni ver sity of Sci ence and Tech nol ogy, Fac ulty of Ge ol ogy, Geo phys ics and En vi ron men tal Pro tec tion, al. A. Mickiewicza 30, 30-059 Krakow, Po land 4 Geo log i cal In sti tute of Dionýz Štúr, Mlynská dol ina 1, SK-81704 Bratislava, Slo vak Re pub lic Budzyñ, B., Jastrzêbski, M., Kozub-Budzyñ, G.A., Koneèný, P., 2015. Monazite Th-U-to tal Pb geo chron ol ogy and P-T thermo dy namic mod el ling in a re vi sion of the HP-HT meta mor phic re cord in granu lites from Stary Giera³tów (NE Orlica-OEnie¿nik Dome, SW Po land). Geo log i cal Quar terly, 59 (4): 700-717, doi: 10.7306/gq.1232Ther mo dy namic mod el ling, geothermometric cal cu la tions and monazite Th-U-to tal Pb dat ing via elec tron microprobe anal ysis were used to im prove the pres sure, tem per a ture and tim ing con straints of the HP-HT meta mor phic re cord in granu lites from Stary Giera³tów (NE Orlica-OEnie¿nik Dome, SW Po land). The new data con strained the P-T con di tions to 20-22 kbar and ca. 900-920°C, fol lowed by de com pres sion to ca. 16-18 kbar in the fel sic-to-in ter me di ate granu lites and 18-20 kbar and ca. 950-970°C in the mafic granulite. The lat ter con di tions are con sid ered to closely rep re sent the peak tem per a tures ex pe ri enced by these rocks. In the in ter me di ate granulite, the ma trix monazite and monazite in clu sions in gar net and al la nite yielded an age of 349 ± 2.5 Ma. A HP-HT meta mor phic event with tem per a ture con di tions ex ceed ing 900°C, which are greater than the clo sure tem per a tures of most geochronometers, must have dis turbed and com pletely re set the iso to pic systems, in clud ing the Th-U-Pb sys tem in the monazite. Con se quently, this re set ting pre vented us from con strain ing the age of po ten tial ear lier meta mor phic events or the ig ne ous protolith. The 349 ± 2.5 Ma age is in ter preted as the tim ing of the late-stage HP-HT event and cool ing be low 900°C re lated to the ini tial ex hu ma tion of the granu lites. A com par i son of the new P-T-t con straints with pre vi ous data from the NE Orlica-OEnie¿nik Dome in di cates that the ac ti va tion of the chan nels that exhumed the HP rocks to mid dle crustal depths most likely ini ti ated at ca. 349 Ma, and that all of the meta mor phic rocks in the Orlica-OEnie¿nik Dome likely shared a com mon Variscan evo lu tion af ter ca. 340 Ma.

Integrating X‐ray mapping and microtomography of garnet with thermobarometry to define the P–T evolution of the (near) UHP Międzygórze eclogite, Sudetes, SW Poland

“…Geochronological studies from the nearby granulites and surrounding rocks establish a time frame for the exhumation process (Anczkiewicz et al., ; Budzyń, Jastrzębski, Kozub‐Budzyń, & Konečný, ; Klemd & Bröcker, ; Lange et al., ; Walczak et al., ). Exhumation commenced at 349–347 Ma (Budzyń et al., ; Walczak et al., ) and after c . 6 Ma (342 Ma) reached the stage of zircon crystallization and recrystallization on the retrograde path (Turniak et al., ; Walczak et al., ).…”

“…Geochronological studies from the nearby granulites and surrounding rocks establish a time frame for the exhumation process (Anczkiewicz et al, 2007;Budzyń, Jastrzębski, Kozub-Budzyń, & Konečný, 2015;Klemd & Bröcker, 1999;Lange et al, 2005;Walczak et al, 2017). Exhumation commenced at 349-347 Ma (Budzyń et al, 2015;Walczak et al, 2017) and after c. 6 Ma (342 Ma) reached the stage of zircon crystallization and recrystallization on the retrograde path (Turniak et al, 2000;Walczak et al, 2017). Subsequent fast uplift is revealed by the successive closure of Sm-Nd (Lange et al, 2005;Walczak et al, 2017) Rb-Sr (Lange et al, 2002), and Ar-Ar (Maluski et al, 1995;Marheine et al, 2002;Steltenpohl et al, 1993) isotopic systems over a period of 10-12 Ma.…”

Multiphase magmatic activity in the Variscan Kłodzko–Złoty Stok intrusion, Polish Sudetes: evidence from SHRIMP U–Pb zircon ages

“…A Pb-Pb single zircon evaporation age of an amphibole-biotite granodiorite yielded an age of 353 ± 1 Ma (Skrzypek et al 2014). CHIME dating of monazite from a muscovite-biotite granodiorite and host metamorphic rocks points to an emplacement age (~ 343 Ma) within the age range of the KZSI (Budzyń et al 2015;Budzyń and Jastrzębski 2016). This may indicate that the KZSI and Jawornik bodies were part of the same magmatic system.…”

Monazite stability and the maintenance of Th-U-total Pb ages during post-magmatic processes in granitoids and host metasedimentary rocks: A case study from the Sudetes (SW Poland)

“…The an a lyt i cal strat egy and de tails fol lowed those used in Budzyñ et al (2015a). Monazite was ana lysed us ing a 15 kV ac cel er at ing volt age, a 180 nA beam cur rent and a 3 µm size of beam fo cused on carbon-coated thin sec tion.…”