Annales Societatis Geologorum Poloniae (2015), vol. 85: 405-424. doi: http://dx.doi.org/10.14241/asgp.2015.016 STABILITY OF MONAZITE AND DISTURBANCE OF THE Th-U-Pb SYSTEM UNDER EXPERIMENTAL CONDITIONS OF 250-350 °C AND 200-400 MPa Bartosz BUDZYŃ1’ 2, Patrik KONECNY3 & Gabriela A. KOZUB-BUDZYŃ4 1 Institute of Geological Sciences, Polish Academy of Sciences, Research Centre in Kraków ING PAN, Senacka 1, PL-31002 Kraków, Poland; e-mail: ndbudzyn@cyf-kr.edu.pl 2 Institute of Geological Sciences, Jagiellonian University, Oleandry 2a, PL-30063 Kraków, Poland Dionyz Stur State Geological Institute, Mlynska dolina 1, SK-81704 Bratislava, Slovak Republic; e-mail: patrik.konecny@geology.sk 4 AGH University of Science and Technology, Faculty of Geology, Geophysics and Environmental Protection, Mickiewicza 30, PL-30059 Krakow, Poland; e-mail: lato@agh.edu.pl Budzyń, B., Konecny, P. & Kozub-Budzyń, G. A., 2015. Stability of monazite and disturbance of the Th-U-Pb system under experimental conditions of 250-350 °C and 200-400 MPa. Annales Societatis Geologorum Poloniae, 85: 405-424. Abstract: This experimental study provides important data filling the gap in our knowledge on monazite stability under conditions of fluid-mediated low-temperature metamorphic alteration and post-magmatic hydrothermal alterations. The stability of monazite and maintenance of original Th-U-total Pb ages were tested experimentally under P-T conditions of 250-350 °C and 200-400 MPa over 20-40 days. The starttng materials included the Burnet monazite + K-feldspar ± albite ± labradorite + muscovite + biotite + SiO2 + CaF2 and 2M Ca(OH)2 or Na2Si2Ö5 + H2O fluid. In the runs with 2M Ca(OH)2, monazite was unaltered. REE-enriched apatite formed at 350 °C and 400 MPa. The presence of the Na2Si2O5 + H2O fluid promoted the strong alteration of monazite, the formation of secondary REE-enriched apatite to fluorcalciobritholite, and the formation of REE-rich steacyite. Monazite alteration included the newly developed porosity, patchy zoning, and partial replacement by REE-rich steacyite. The unaltered domains of monazite maintained the composition of the Burnet monazite and its age of (or close to) ca. 1072 Ma, while the altered domains showed random dates in the intervals of 375-771 Ma (250 °C, 200 MPa run), 82-253 Ma (350 °C, 200 MPa), and 95-635 Ma (350 °C, 400 MPa). The compositional alteration and disturbance of the Th-U-Pb system retulted from fluid-mediated coupled dis solution-reprecipitation. In nature, such age disturbance in monazite can be attributed to post-magmatic alteration in granitic rocks or to metasomatic alteration during metamorphism. Recognition of potentially altered domains (dark patches in high- contrast BSE-imaging, developed porosity or inclusions of secondary minerals) is crucial to the application of Th-U-Pb geochronology. Key words: Monazite, apatite, steacyite, rare earth elements, geochronology, experimental petrology. Manuscript received 12 November 2014, accepted 25 May 2015 INTRODUCTION Monazite (REEPO4) is one of the main hosts of rare earth elements (REE) and actinides in the Earth’s crust. The stability of monazite, strongly dependent on temperature, pressure, and composition of host rock and fluid, has been widely studi ed in terms of alt eration and replacement by apatite, allanite and epidote, recognized in igneous rocks af- fected by a fluid-mediated overprint (e.g., Broska and Si- man, 1998; Broska et al., 2005), and amphibolite-facies me- tamorphic rocks (e.g., Finger et al., 1998; Majka and Budzyń, 2006; Janots et al., 2008; Budzyń et al., 2010; Ondrejka et al., 2012). It has been known for half a century that monazite may be stable in Ca-poor granitic rocks (bulk composition of <0.7 wt % CaO) and that allanite is present in Ca-rich granttes (>1.8 wt % CaO), while both monazite and allanite are stable in intermediate granites with 0.7-1.8 wt % CaO bulk content (Lee and Dodge, 1964; Lee and Bas- tron, 1967). The stability relationships between monazite and allanite under upper greenschist- to amphibolite-facies conditions were constrained via thermodynamic modelling (Janots et al., 2007; Spear, 2010). There are also experimen- tal data, which repticate the mineral compo tition of the whole rock to determine the relative stabilities of monazite, 406 B. BUDZYŃ ET AL. allanite, and apatite under upper greenschist- to amphibo- lite-facies conditions (Budzyń et al., 2011), and recently ex- panded to a wide P-T range of 450-750 °C and 2-10 kbar (Budzyń et al., 2014). However, there are limtted data on monazite stability during low-temperature hydrothermal and diagenetic processes (Poitrasson et al., 1996, 2000; Cuney and Mathieu, 2000; Hecht and Cuney, 2000; Read et al., 2002; Rasmussen and Muhling, 2007, 2009). The incorporation of Th and U in monazite offers the potential for Th-U-Pb dating (Parrish, 1990). Because of the negligible content of common Pb relative to radiogenic Pb, a monazite age can be constrained by “chemical” Th-U-total Pb dating ustng the electron microprobe (Suzuki and Ada- chi, 1991; Montel et al., 1996; Konecny et al., 2004; Jerci- novic and Williams, 2005; Pyle et al., 2005; Williams et al., 2007; Jercinovic et al., 2008; Suzuki and Kato, 2008; Spear et al., 2009). Electron microprobe microanalysis is a power- ful tool to link monazite ages with textural content and put absotute time constraints on metamorphic, metasomatic or deformational processes, constrain rates of these processes, and finally, to put absotute time constraints on the recon- struction of pressure-temperature-deformation paths (Wil- liams and Jercinovic, 2002; Williams et al., 2007). Because of these considerations, monazite became one of the most commonly used geochronometers in the last two decades. Monazite is characterized by high diffusional closure tem- perature of 800-900 °C, with respect to Th and Pb (Cher- niak et al., 2004; Gardes et al., 2006; Cherniak and Pyle, 2008). However, an age disturbance was recognized typt- cally in monazite revealing patchy zoning, related to fluid- aided coupled dissolution-reprecipitation during post-mag- matic, metasomatic or hydrothermal alteration in granitic (Townsend et al., 2000; Petrik and Konecny, 2009; Appel et al., 2011; Tartese et al., 2011; Ayers et al., 2013; Lisowiec et al., 2013) and metamorphic rocks (Aleinikoff et al., 2012). Knowledge about the advantages and limitations of using monazite as a geochronometer expanded significantly during the last decade with respect to possible disturbance of the Th-U-Pb system. Experimental studies shown that al- teration of monazite rel ated to the fluid-mediated coupled dissolution-reprecipitation process may significantly dis- turb Th-U-Pb system (Teufel and Heinrich, 1997; Seudoux- Guillaume et al., 2002a; Harlov et al., 2007, 2011; Harlov and Hetherington 2010; Hetherington et al., 2010; Budzyń et al., 2011), leading to resetting of the monazite clock, even far betow the diffusional clo ture temperature, that is at 450 °C and 450 MPa (Williams et al., 2011). The aim of this study was to experimentally explore and constrain the stability of monazite under conditions of 250- 350 °C and 200-400 MPa, in the presence of two of the most aggressive flui ds, previously used by Budzyń et al. (2011). The innovation of this work lies in utilizing a min- eral assemblage that roughly replicates the composition of granitic rocks. The new experimental data provide petrolog- ical implications for applications of monazite in reconstruc- ting low-grade metamorphic processes. Further geochronol- ogical implications are related to the experimental distur- bance of the Th-U-Pb system in monazite, significantly mo- difying the original age. ANALYTICAL AND EXPERIMENTAL METHODS Analytical methods The starting minerals and experimental products were evaluated ustng a Hitachi S-4700 field emission scanning electron micro tcope (FESEM), equipped with an energy dispersive spectrometer (EDS), at the Institute of Geologi- cal Sciences, Jagiellonian University (Kraków, Poland). The chemical analyzes of minerals were performed us- ing a Cameca SX 100 electron microprobe equipped with a four-wavelength spectrometer, at the Department of Special Lab o rato ries, Lab o ratory of Elec tron Microanalysis, Geo- logical Institute of Dionyz Stur (Bratislava, Slovak Repub- lic). The monazite was analyzed using a 15 kV accelerating voltage, a 180 nA beam current, and a 3-gm beam size fo- cused on the grain mount, coated with ca. 25 nm carbon film. The foltowtng natutal and synthetic standards, and corresponding spectral lines were used: apatite (P Ka), PbCO3 (Pb Ma), ThO2 (Th Ma), UO2 (U Mß), YPO4 (Y La), LaPO4 (La La), CePO4 (Ce La), PrPO4 (Pr Lß), NdPO4 (Nd La), SmPO4 (Sm La), EuPO4 (Eu Lß), GdPO4 (Gd La), TbPO4 (Tb La), DyPO4 (Dy Lß), HoPO4 (Ho Lß), ErPO4 (Er Lß), TmPO4 (Tm La), YbPO4 (Yb La), LuPO4 (Lu Lß), fayatite (Fe Ka), barite (S Ka), wol- lastonite (Ca Ka, Si Ka), SrTiO3 (Sr La), Al2O3 (Al Ka), GaAs (As La). The counting times on peak/background (in sec.) were as follows: P 10/10, Pb 300/150, Th 35/17.5, U 80/80, Y 40/20, La 5/5, Ce 5/5, Pr 15/15, Nd 5/5, Sm 5/5, Eu 25/25, Gd 10/10, Tb 7/7, Dy 35/35, Ho 30/30, Er 50/50, Tm 15/15, Yb 15/15, Lu 100/100, Fe 5/5, S 10/10, Ca 10/10, Sr 20/20, Al 10/10, Si 10/10, As 120/120. The monazite con- centrations were recalculated using age equations from Montel et al. (1996) and evaluated using in-house DAMON software (P. Konecny, unpublished). Additional analytical information can be found in Konecny et al. (2004), Petrik and Konecny (2009) and Vozärovä et al. (2014). Apatite, fluorcalciobritholite and REE-rich steacyite were anatyzed using two conditions, automatically switched during a run from (1) 15 kV, 20 nA for F (30/15 sec), Si (10/5), Na (10/5), Al (10/5), Mg (10/5) P (10/5), Ca (10/5), K (10/5), Cl (10/5), Fe (10/5), Mn (10/5), Ti (10/5); to (2) 15 kV, 80 nA for Y (30/15), Sr (60/30), Pb (30/15), Ce (40/20), La (40/20), Nd (30/15), Pr (50/25), Sm (30/15), Eu (60/30), Gd (40/20), Tb (20/10), Dy (60/30), Th (30/15), U (40/20), and a 1-5 gm beam size, depending on the size of the grain ana- lyzed. Silicate minerals were analyzed using 15 kV acceler- ating voltage, 20 nA current, and beam size of 5 gm for bio- tite, K-feldspar, and 10 gm for muscovite, albite and labra- dorite. The counting times were 10 sec. on peak and 5 sec. on background for each element. Additional analyses of silicates and compositional X-ray maps of altered monazite were performed usrng a JEOL SuperProbe JXA-8230 electron microprobe at the Laboratory of Critical Elements AGH-KGHM, Faculty of Geology, Geophysics and Environmental Protection, AGH University of Science and Technology (Kraków, Potand). The silicates were analyzed using a 15 kV accelerating volt- age, 20 nA beam current, and focused beam to 5 gm beam size. The counting times on peak/background (in sec.) were STABILITY OF MONAZITE AND DISTURBANCE OF THE Th-U-Pb SYSTEM 407 20/10 for Si, and 10/5 for other elements in feldspars and micas. Compositional X-ray maps were collected at 15 kV, 100 nA, 100 ms dwell time, 0.33 pm step size and 0.3 pm beam size. Experiments The experiments were performed at the Deutsche Geo- ForschungsZentrum (Potsdam, Germany), using cold-seal autoclaves on a hydrothermal line. The P-T conditions used and corresponding duration of the experiments were 250 °C, 200 MPa, 40 days; 350 °C, 200 MPa, 40 days; and 350 °C, 400 MPa, 20 days (Table 1). The experiments utilized an as- semblage of monazite + K-feldspar + albite Ab100 (or labra- dorite An60Ab37Kfs3) + muscovite + biotite + synthetic SiO2 + CaF2 (Suprapur, Merck). Amorphous SiO2 was used in- stead of quartz to increase the reaction rate and CaF2 was used as a source of Ca and F to form fluorapatite. The monazite used in the experiments originated from a pegmatite in Burnet County, Texas, U.S.A. A fragment of the monazite cryst al was crushed and sieved to obt ain the 50-250 pm fraction. Optically clear to foggy, reddish brown grains were hand-picked under the binocu-ar microscope, fol-owed by wash-ng in ethanol in an ultrasonic bath. The grains revealed faint zonation and patchtness in the cross- section under high-contrast backscattered electron (BSE) imagtng, which is mostly retated to the variation in ThO2, ranging from 9.40 to 16.95 wt % (Table 2). The Th-U-total Pb age of the monazite was constrained to 1072 ± 2.8 Ma (MSWD = 1.18, n = 53; Fig. 1; Appendix 3) using the elec- tron microprobe. A simtt ar Th-U-total Pb age of 1096 ± 8 Ma was previously obtained by M. J. Jercinovic (in Ruschel et al., 2012). The selected silicate mineral assemblage is similar to the assemblage used in previous experiments by Budzyń et al. (2011). The minerals included a hydrothermal albite (Ab100; Roznava, Slovak Republic), labradorite (An60Ab27Kfs3; Chihuahua, Mexico), sanidine (Eifel region, Germany), mus- covite from a pegmatite (Siedlimowice, Sudetes, Potand), and biotite (gneiss, Sikkim Himalaya, India). The minerals were crushed and sieved to a 50-250 pm fraction, foltowed by washing in ethanol in an ultrasonic bath. The foreign or al- tered mineral grains were hand-picked under a binocular mi- croscope. The fluids used included 2M Ca(OH)2 to test if al- lanite would form in terms of the relative stabilities of monazite and altanite, and Na2Si2O5 + H2O to test for the remobilization of REE, Th, U and Pb, and to maint ain Th-U-total Pb ages of monazite. Solid mixes were prepared by mixtng the weighed portions of individual minerals to- gether dry (Table 1). The mineral mix and fluid were loaded into Au capsules, 3 mm wide and 15 mm long, that were arc-welded shut ustng a Lampert PUK U3 argon plasma torch. The capsules were checked for leaks by first weigh- ing, then placing them in a 105 °C oven overnight, and then weighing them again. Experiments were conducted using a standard cold- seal, 6 mm bore, Rene metal autoclaves with H2O as the pressure medium. Four gently flattened Au capsules, two for monazite (this study) and two for subsequent xenotime experiments (Budzyń and Kozub-Budzyń, 2015), were placed in each of three autoclaves with Ni-NiO filler rods. Pressures were sta- ble during the experiments. Temperatures were measured externally, with the tip of a Ni-Cr thermocouple, placed in a special hole drilled into the autoclave near the location of the capsules, and are betieved to be accurate to within ± 5 °C. After a run, the autoclaves were quenched ustng compre- ssed air, reaching temperatures of ca. 100 °C within 1 min. The capsules were cleaned, weighed, opened, and dried at 105 °C. Part of the experimental products extracted from a Au capsule was mounted in epoxy and polished. A second part of the reacted mineral mix was sprinkled on the SEM mount with adhes ive carbon tape and carbon coated for BSE imaging. Fig. 1. The characteristics of the Burnet monazite used in the experiments. A, B. Results of Th-U-total Pb dating of the Burnet monazite. C. Plot of formula proportions of (REE + Y + P) vs. (Th + U + Si), calcuiated on the basis of 4 oxygen atoms, presenting huttonitic substitution of (Th, U)SiREE-1P-1 and cheralitic substi- tution of Ca(Th, U)REE-2 (cf., Förster, 1998; Linthout, 2007). 408 B. BUDZYŃ ET AL. Experimental conditions and starting materials (mg) Table 1 T P Dura¬ Total in Solids Mineral Exp. [°C] [MPa] tion Mnz Ab Lbr Kfs Bt Ms SiO2 CaF2 Ca(OH)2 Na2Si2O5 h2o Total Au added products Remarks [days] capsule* M12 250 200 40 5.18 - 3.97 3.03 4.00 2.03 3.92 2.85 0.79 - 5.22 30.99 30.36 25.14 Wo Starting minerals are not C-04 altered. Wollastonite formed. M12 350 200 40 5.12 - 4.21 3.08 3.91 1.99 3.87 2.84 0.78 - 5.29 31.09 30.85 25.56 Wo Starting minerals are not C-05 altered. Wollastonite formed. M12 Delicate crystals of C-15 350 400 20 5.00 - 4.05 3.40 4.05 2.30 3.97 3.10 0.79 - 5.27 31.93 31.10 25.83 REE-Ap REE-enriched apatite formed on the monazite surface. Monazite shows strong M12 dissolution with porosity and N-04 250 200 40 5.28 4.18 - 3.03 4.09 1.88 3.89 3.26 - 5.05 5.15 35.81 35.36 30.21 Stc patchy internal zoning. K-feldspar achived albite rims. Small steacyite grains formed. Monazite shows strong dissolution with porosity along whole grains, and patchy internal zoning. Delicate REE-Ap, crystals of REE-rich steacyite M12 350 200 40 5.12 4.08 - 2.96 3.83 1.73 4.61 2.80 - 4.26 5.56 34.95 33.79 28.23 Stc, and REE-enriched apatite are N-05 Amph present on the monazite surface. Large grains of REE-rich steacyite also formed. K-feldspar achieved albite rims. Delicate needle-like crystals of amphiboles are present. Monazite shows strong dissolution with porosity along whole grains, and patchy internal zoning. Numerous, M12 REE-Ap, elongated grains of N-15 350 400 20 5.15 4.28 - 3.25 3.98 2.15 4.01 3.02 - 5.09 5.36 36.29 35.43 30.07 Stc, REE-enriched apatite to Amph fluorcalciobritholite formed. REE-rich steacyite formed. K-feldspar achived albite rims. Delicate needle-like crystals of amphiboles are present. * Difference between Total and Total in Au capsule is related to weight loss during charging the capsule with solids. Ab - albite, Amph - amphibole, Bt - biotite, Kfs - K-feldspar, Lbr - labradorite, Mnz - monazite, Ms - muscovite, REE-Ap - REE-enriched apatite, Stc - REE-rich steacyite, Wo - wollastonite. EXPERIMENTAL RESULTS Experiments with 2M Ca(OH)2 The monazite and other starting minerals showed no signs of alteration (Fig. 2), except for the formation of tiny crystals of REE-enriched apatite on the surface of monazite from the run at 350 °C and 400 MPa (M12C-15). Wollasto- nite was the second phase formed under conditions of 250- 350 °C and 200 MPa (Fig. 2B, C). The chemical composi- tion of monazite, feldspars and micas after the experiments showed no differences with respect to composition of the origtnal minerals (Table 2; Appendix 1 and 2). The small size of the wollastonite and REE-enriched apatite prevented accurate electron microprobe analyses and both phases were identified using SEM-EDS analyses. Experiments with Na2Si2O5 + H2O Alteration of the monazite, including dissolution pits developed on the grain surfaces, was observed in all runs (Fig. 3A, E, H). In cross-section, porosity developed along the monazite rims under conditions of 250 °C and 200 MPa, leaving the cores unaltered (M12N-04; Fig. 3A). The poros- ity across whole grains formed at 350 °C and 200 MPa (M12N-05; Fig. 3C, D). The monazite with developed pores showed also patchy zoning under high-contrast BSE imag- ing (Fig. 3C). Increastng pressure to 400 MPa at the same temperature of 350 °C resulted in the development of poros- ity in the monazite, filled with a phase showing a composi- tion simit ar to that of steacyite [(K,D)(Na, Ca)2(Th, U) Si«O20], significantly enriched in REE (Table 3). The ex- perimental products included a rare alteration texture of the monazite with pores showing preferred orientation and filled with REE-rich steacyite, across the monazite rim, and a weakly preserved unaltered monazite core (Fig. 4A). The chemkal composition of the monazite differed in both bright and dark compositional domains (Table 2, Figs 3, 4A). The bright areas had a composition, similar to that of the original Burnet monazite. The most noticeable compo- sitional changes in the dark patches were related to a deple- tion in PbO to 0.01-0.18 wt % vs. 0.48-0.86 wt % in the original Burnet monazite. Also UO2 was depleted to 0.04- 0.14 wt % in the dark areas vs. 0.26-0.49 wt % in the Burnet monazite. The ThO2 content in the dark areas varied from Average results of the electron microprobe analyzes of monazite STABILITY OF MONAZITE AND DISTURBANCE OF THE Th-U-Pb SYSTEM 409 OJ 2 H OS OS st so o OO "c3 r~- CD oo St o SO d cs o cs d cs so d o CS so cs o cs d o cs Ph o d d d d o d d d d d o o d O CD CD CD CD CD oo 3 V V V V OS CD OO a pv CD oo CD o a st a rv 3 Gd203 Tb203 DyOC Ho2°3 Er203 Tm23 Yb203 Lu2°3 Mg° Ca° Mn° Fe° Sr° Pb° Na2° k2o F C1 Total ^+ree)2o3 M12N-04, 250°C, 200 MPa, 40 days 1-1 ^taz-int <0---2 56---3 ---2 ---6 ---2 ---2 ---5 ---8 ---7 ---1 ---3 ---1 ---3 ---6 ---1 0--- ---a--- ---a--- ---a--- ---a--- ---a--- ---1 ---9 ---1 ---9 ---1 ---5 ---1 ---9 ---1 ---1 ---5 ---4 2-1 ^taz-int <0---2 57---1 <0---2 22.15 0.56 <0---2 0---1 <0---8 0---4 0.13 0---9 0.90 0.15 1---5 0---2 1---3 ---a--- ---a--- ---a--- ---a--- ---a--- <0---1 639 <0---1 0---6 0---4 <0---5 438 5---4 <0---1 <0---1 101---4 5---1 M12N-05, 3^C, 200 Ma, 4, days 1-1 mafrix <0---2 56---6 ---2 ---4 ---9 ---2 ---1 ---8 ---5 ---9 ---4 ---1 ---2 ---5 ---2 0--- ---a--- ---a--- ---a--- ---a--- ---a--- ---1 ---2 ---1 ---9 ---6 ---5 ---5 ---3 ---1 ---1 ---5 ---9 1-2 mafrix 0---3 57--- ---7 ---6 ---6 ---3 ---5 ---8 ---9 ---8 ---1 ---6 ---0 ---6 ---6 1.14 ---a--- ---a--- ---a--- ---a--- ---a--- ---1 ---9 ---1 ---9 ---3 ---5 ---5 ---1 ---1 ---1 ---5 ---5 2-1 ^taz-int 1.20 55---1 0---9 19--- 0---1 <0---2 1---1 0.13 0---2 0---1 0.70 0--- <0---9 1---6 0--- 1.31 n.a--- n.a. n.a--- n.a. n.a. 0---9 7.80 0---2 0---4 <0---1 0---6 3---6 4---7 <0---1 <0---1 100---5 6.60 3-1 ^taz-int <0---2 57.78 ---2 ---8 ---4 ---2 ---7 ---8 ---3 ---7 ---3 ---4 ---9 ---3 ---1 1---6 ---a--- ---a--- ---a--- ---a--- ---a--- ---1 ---7 ---1 ---1 ---1 ---5 ---9 ---1 ---1 ---1 ---2 ---4 3-2 ^taz-int <0---2 57.40 ---2 ---9 ---1 ---2 ---9 ---8 ---4 ---4 ---2 ---8 ---9 ---4 ---1 1---5 ---a--- ---a--- ---a--- ---a--- ---a--- ---1 ---6 ---3 ---2 ---1 ---5 ---4 ---3 ---1 ---1 ---6 7.27 M12N-15, 3^C, 400 Ma, 2, days 1-1 mafrix <0---2 57---2 ---5 ---8 ---0 ---1 ---3 ---8 ---1 ---9 ---0 ---4 ---9 ---1 ---6 1---3 ---0 ---6 ---8 ---8 ---4 ---1 ---6 ---1 ---0 ---3 ---5 ---1 ---2 ---1 ---1 ---9 ---2 1-2 mafrix <0---2 57---7 ---6 ---0 ---4 ---1 ---7 ---0 ---2 ---4 ---9 ---9 ---9 ---3 ---5 1---1 ---0 ---8 ---8 ---6 ---8 ---1 ---0 ---2 ---3 ---1 ---5 ---2 ---4 ---1 ---1 ---0 ---2 2 mafrix <0---2 56--- 0---5 17--- 0.50 <0--- 0---4 0--- 1.59 0---5 1 --- 1.54 <0---9 138 0.24 0---9 <0.10 0---3 <0---8 0---0 <0.14 <0---1 8---3 <0---1 <0---1 <0---1 <0---5 2---2 4--- <0---1 <0---1 99---5 8---2 3 mafrix <0---2 56---2 ---2 ---5 ---1 ---1 ---8 ---8 ---8 ---7 ---7 ---2 ---9 ---2 ---2 1---3 ---0 ---6 ---8 ---3 ---4 ---1 ---4 ---1 ---4 ---1 ---5 ---5 ---7 ---1 ---1 ---5 ---7 4 mafrix <0---2 57.18 ---6 ---4 ---4 ---1 ---9 ---5 ---7 ---7 ---3 ---6 ---9 ---0 ---7 0--- ---0 ---9 ---8 ---0 ---4 ---1 ---4 ---1 ---1 ---3 ---5 ---5 ---5 ---1 ---1 ---3 ---1 [c.p.f.u.] Analysis Comment P Si Ti Th u A1 Y La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Mg Ca Mn Fe Sr Pb Na K F C1 Total y+ree M12N-04, 2^C, 200 Ma, 4, days 1-1 ^taz-int 0---0 7---5 ---3 ---0 ---3 ---0 ---1 ---0 ---4 ---6 ---1 ---4 ---6 ---5 ---0 0---6 ---a--- ---a--- ---a--- ---a--- ---a--- ---0 ---9 ---0 ---1 ---0 ---0 ---6 ---0 ---0 ---0 ---0 ---4 2-1 ^taz-int 0---0 7---1 0---4 0---6 0---7 0---0 0---9 0---0 0---2 0---6 0---4 0---3 0---7 0---8 0---0 0---6 ---a--- ---a--- ---a--- ---a--- ---a--- 0---0 0---6 0---0 0---7 0---3 0---0 1---9 1---9 0---0 0---0 12---9 0---6 M12N-05, 350°C, 2,0 Ma, 4, days 1-1 manix 0---0 7---3 ---3 ---0 ---5 ---0 ---2 ---0 ---9 ---5 ---2 ---4 ---5 ---9 ---0 0---6 ---a--- ---a--- ---a--- ---a--- ---a--- ---0 ---0 ---0 ---1 ---5 ---0 ---7 ---3 ---0 ---0 ---8 ---3 1-2 manix 0---3 7---5 ---8 ---8 ---0 ---5 ---3 ---0 ---5 ---9 ---0 ---6 ---4 ---9 ---2 0---1 ---a--- ---a--- ---a--- ---a--- ---a--- ---0 ---7 ---0 ---0 ---3 ---0 ---8 ---0 ---0 ---0 ---6 ---9 2-1 ^taz-int 0---1 7---1 0---9 0---3 0---5 0---0 0---0 0---7 0---2 0---6 0---5 0---7 0---4 0---9 0---3 0---9 n.a--- n.a. n.a. n.a. n.a. 0---9 1---0 0---3 0---2 0---0 0---2 1---8 1---4 0---0 0---0 12---7 0---0 3-1 ^taz-int 0---0 7---7 ---0 ---0 ---3 ---0 ---2 ---0 ---2 ---3 ---1 ---9 ---4 ---5 ---8 0---7 ---a--- ---a--- ---a--- ---a--- ---a--- ---0 ---7 ---0 ---0 ---0 ---1 ---9 ---8 ---0 ---0 ---8 0---1 3-2 ^taz-int 0---0 7---9 ---0 ---1 ---3 ---0 ---1 ---0 ---8 ---2 ---0 ---7 ---3 ---6 ---8 0---7 ---a--- ---a--- ---a--- ---a--- ---a--- ---0 ---4 ---4 ---3 ---0 ---2 ---8 ---6 ---0 ---0 ---3 ---3 M12N-15, 350°C, 4Q0 0a, 2, days 1-1 mafrix ---0 ---6 ---5 ---0 ---5 ---0 ---1 ---0 ---1 ---0 ---4 ---8 ---4 ---9 ---6 0---4 ---0 ---6 ---0 ---8 ---0 ---0 ---6 ---0 ---2 ---2 ---0 ---2 ---6 ---0 ---0 ---4 ---0 1-2 mafrix 0---0 ---0 ---6 ---4 ---7 ---0 ---1 ---0 ---7 ---2 ---8 ---5 ---4 ---1 ---1 0---5 ---0 ---2 ---0 ---7 ---8 ---0 ---5 ---3 ---3 ---0 ---0 ---5 ---1 ---0 ---0 ---6 ---1 2 mafrix 0---0 7---0 0---6 0---4 0---6 0---0 0---2 0---9 0---1 0---3 0---4 0---4 0---3 0---4 0---1 0---0 0---0 0---0 0---0 0---0 0---0 0---0 1---5 0---0 0---0 0---0 0---0 0---3 1---2 0---0 0---0 12---7 0---2 3 mafrix 0---0 ---7 ---0 ---7 ---9 ---0 ---5 ---0 ---5 ---9 ---3 ---4 ---4 ---6 ---5 0---4 ---0 ---0 ---0 ---0 ---4 ---0 ---3 ---0 ---4 ---0 ---0 ---3 ---4 ---0 ---0 ---6 ---9 4 mafrix 0---3 ---8 ---6 ---4 ---7 ---0 ---8 ---8 ---0 ---3 ---5 ---9 ---3 ---5 ---2 0---5 ---0 ---3 ---0 ---4 ---4 ---0 ---3 ---0 ---0 ---2 ---0 ---4 ---1 ---0 ---0 ---8 ---0 Notes: cations per formula uw— (c.p.f.u.) are calculated on the basis of 20 oxygen atoms; n.a. — not analyzed; mafrix - individual grain of OE-steacyite; Mnz-int — REE-rich steacyite intergrown with monazite. Table 4 Results of the electron microprobe analyzes of REE-rich apatite to fluorcalciobritholite formed in experiments with Na2Si2O5 + HO fluid [wt %] p2o5 Si02 Ti02 Th02 uo2 ai2o3 y2o3 La203 Ce203 Pr2°3 Nd2°3 Sm203 Eu203 Gd203 Tb203 DyO Ho2°3 Er2°3 Tm2O3 Yb2O3 Lu2°3 Mg° Ca° Mn° Fe° Sr° Pb° Na2° k2o F ce Sum 0=(F+C1) totae F+m:e)2o3 M12N-05, 350°C, 200 MPa, 40 days 1 26---5 5---0 046 2---1 ---1 ---0 ---5 ---0 ---1 ---1 ---2 ---2 ---4 ---7 ---8 ---4 n.a--- ---a--- ---a--- ---a--- ---a--- ---5 ---8 ---6 ---2 ---1 ---7 ---7 ---0 ---1 ---1 ---0 ---4 ---7 ---0 2 29.56 1.76 0---6 2---5 0---4 <0---1 0---7 446 1549 2.40 648 3---7 <0---4 2---1 0---2 1---7 n.a--- n.a. n.a. n.a. n.a. <0---1 23---2 <0---1 0---2 044 0---6 3--- 0---4 2---7 0---3 101---8 143 100---5 37---7 3 29.70 1 --- 1 <0---1 0---7 ---1 ---4 0---8 ---2 ---1 ---3 ---5 ---4 ---4 ---1 ---8 ---5 n.a--- ---a--- ---a--- ---a--- ---a--- ---1 ---3 ---4 ---5 ---0 ---5 ---9 ---1 ---4 ---1 ---0 ---1 ---8 ---7 M12N-15, 350°C, 400 MPa, 20 days 1 32.75 0---5 <0---1 ---4 ---2 ---2 ---5 ---5 ---2 ---0 ---7 ---7 ---5 ---8 ---7 ---7 ---5 ---1 ---8 ---9 ---2 ---1 ---1 ---1 ---1 ---6 ---2 ---7 ---9 ---9 ---1 ---1 ---2 ---9 ---9 2 32---3 0.74 0---3 046 0.19 <0.41 0---1 2.50 10---4 1---1 6---5 3--- <0---4 240 0---4 1---5 0---6 0---7 0---6 0---9 <0---4 <0.41 27---3 <0---1 <0.41 0---7 0---2 443 0---5 249 <0.41 9945 0---2 ---3 3140 [c.p.f.u.] P Si Ti Th U Ae Y La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Mg Ca Mn Fe Sr Pb Na K F ce Totae Y+REE M12N-05,350°C, 200 MPa, 40 days 1 2---9 0---9 0---5 ---9 ---0 ---2 ---4 ---0 ---9 ---9 ---4 ---3 ---0 ---0 ---9 ---7 0---0 ---0 ---0 ---0 ---0 ---3 ---6 ---7 ---6 ---7 ---2 ---0 ---3 ---6 ---0 ---0 ---6 2 2---5 0---3 0---5 0---3 0---1 0---0 0---2 0---2 0---1 0---1 0---8 0---8 0---0 0---9 0---1 0---6 0---0 0---0 0---0 0---0 0---0 0---0 2---4 0---0 0---8 0---8 0---2 0---9 0---0 0---7 0---5 8---6 1---8 3 2---0 0---9 0---0 ---4 ---0 ---5 ---8 ---4 ---1 ---3 ---1 ---2 ---0 ---5 ---3 ---6 0---0 ---0 ---0 ---0 ---0 ---0 ---1 ---4 ---5 ---6 ---4 ---0 ---2 ---0 ---0 ---4 ---4 M12N-15,350°C, 400 MPa, 20 days 1 2---6 0---6 0---0 ---3 ---5 ---2 ---6 ---9 ---1 ---3 ---3 ---4 ---2 ---3 ---6 ---5 0---2 ---0 ---3 ---3 ---4 ---0 ---2 ---0 ---0 ---5 ---1 ---3 ---1 ---4 ---0 ---1 ---3 2 2---0 0---5 0---2 0---4 0---4 0---0 0---4 0---4 0---7 0---7 0---4 0---0 0---0 0---1 0---5 0---1 0---2 0---9 0---2 0---3 0---0 0---0 3---7 0---0 0---0 0---8 0---1 0---4 0---6 0---4 0---0 8---1 1---7 Notes: cations per formula unit (c.p.f.u.) are calculated on the basis of 13 oxygen atoms; n.a. — not analyzed. STABILITY OF MONAZITE AND DISTURBANCE OF THE Th-U-Pb SYSTEM 413 Fig. 5. Plots of formula proportions of (REE + Y + P) vs. (Th + U + Si) calculated on the basis of 4 oxygen atoms for the monazite in experimental products from runs at 250 °C, 200 MPa, 40 days (A, B), 350 °C, 200 MPa, 40 days (C, D) and 350 °C, 400 MPa, 20 days (E, F). The huttonitic substitution of (Th, U)SiREE-1P-1 and cheralitic substitution of Ca(Th, U)REE-2 are represented by dashed lines (cf., Förster, 1998; Linthout, 2007). The monazite in experimental products from runs with 2M Ca(OH)2 shows pattern similar to that of the starting Burnet monazite. Compositional alteration of the monazite in the presence of Na2Si2O5 + H2O fluid resulted in domination of the huttonitic substitution in the altered domains, whereas the unaltered domains exhibit composition similar to that of the Burnet monazite (Fig. 1C). (Appendix 2). Delicate needle-like grains of Na- and Fe-rich amphibole formed only in the runs at 350 °C and 200-400 MPa (Fig. 3G). Maintaining original Th-U-total Pb ages of monazite during experiments The monazite in the experimental products was ana- lyzed in terms of preserving the original Th-U-total Pb ages. The monazite from runs with 2M Ca(OH)2 yielded ages of 1095 ± 4.6 Ma (250 °C and 200 MPa), 1100 ± 4.8 Ma (350 °C and 200 MPa), and 1088 ± 5.0 Ma (350 °C, 400 MPa; Fig. 6, Appendix 3). Although slightly shifted, these ages are similar to the 1072 ± 2.8 Ma age of the original Burnet monazite, showing that the Th-U-Pb system in the monazite was not disturbed in experiments with 2M Ca(OH)2. The patchy zoned monazite from the runs with Na2Si2O5 + H2O yielded various ages. Bright zones under BSE imag- ing give ages of1074 ± 6.7 Ma (250 °C and 200 MPa), 1081 414 B. BUDZYŃ ET AL. Fig. 6. Results of Th-U-total Pb “dating” ofthe monazite in experimental products from runs at 250 °C, 200 MPa, 40 days (A-C), 350 °C, 200 MPa, 40 days (D-F) and 350 °C, 400 MPa, 20 days (G-I). The monazite from runs with 2M Ca(OH)2 fluid maintain age record of the original Burnet monazite. In contrast, the altered, patchy zoned monazite from experiments with Na2Si2O5 + H2O fluid includes inter- nal domains that preserved the original ages, and domains altered via fluid-aided coupled dissoiution-reprecipitation leading to distur- bance of the Th-U-Pb system. ± 7.3 Ma (350 °C and 200 MPa), and 1084 ± 7.9 Ma (350 °C and 400 MPa). Dark zones with modified compo -itions yielded scattered single Th-U-total Pb dates in ranges of 375-771 Ma (250 °C and 200 MPa; Fig. 6C), 82-253 Ma (350 °C and 200 MPa; Fig. 6F), and 95-635 Ma (350 °C and 400 MPa; Fig. 6I). These dates significantly differ from the original age of 1072 ± 2.8 Ma, indicating disturbance of the Th-U-Pb system in the presence of Na2Si2O5 + H2O. DISCUSSION Interpretation of experimental results The experimental results showed significant differen- ces in products between runs with 2M Ca(OH)2 and Na2Si2O5 + H2O fluids. The experiments with 2M Ca(OH)2 were promismg with regard to monazite alterations, on the basis of previous experiments with similar starting mineral and fluid composit ion that resulted in monazite alt eration and the formation of a secondary apatite-britholite solid so- lution and REE-epidote to allanite at 450-500 °C and 450- 610 MPa (Budzyń et al., 2011). A high-Ca bulk content of the capsule charge, related to presence of labradorite, CaF2, and 2M Ca(OH)2, was expected to promote the formation of apatite. Experiments also tested whether allanite would form preferentially at 350 °C and 200-400 MPa, on the ba- sis of thermodynamic modelling of the relative stabilities of monazite and dissakisite-(La), the Mg-equivalent of allanite (Janots et al., 2007), and the stability relations of monazite and allanite (Spear, 2010). However, small amounts of apa- tite formed only in one experimental run at 350 °C and 400 MPa (M12C-15), but no altanite was formed. The absence of allanite in the products was the outcome least likely to be related to the short duration of experiments. Owing to time limits with respect to natural processes, the fluids were used in excess to increase the reaction rates in the same manner as in the previous experimental study with similar mineral- fluid composition resulting in rapid monazite alteration and allanite growth (Budzyń et al., 2011). The monazite alter- ation and the format ion of all anite were recently reported from experiments in the wide P-T range of 2-10 kbar and 450-750 °C (Budzyń et al., 2014), with similar starting com- positions of soHds and 2M Ca(OH)2 fluid, as in the present study. The transition between the monazite and altanite sta- bility fields must be located between 350 and 450 °C at 200- 400 MPa. The experimental results were consistent with ob- servations from nature that during progressive metamor- phism, replacement of monazite by all anite is subsequent to the appearance of biotite (Wing et al., 2003) or, more specifi- cally, occurred at 420-450 °C (Janots et al., 2006, 2008). STABILITY OF MONAZITE AND DISTURBANCE OF THE Th-U-Pb SYSTEM 415 The strong alteration of monazite in experiments with Na2Si2O5 + H2O was consistent with previous experimental work performed at higher P-T conditions (Hetherington et al., 2010; Harlov and Hetherington, 2010; Budzyń et al., 2011; Harlov et al., 2011). The formation of apatite, fluor- britholite-(Ce) or apatite-fluorbritholite-(Ce) solid solution was expected according to the previous experiments of Budzyń et al. (2011). Although monazite was partially dis- solved in all runs, the apatite- to britholite-group minerals were not stable in the experimental conditions at 250 °C and 200 MPa. REE-enriched apatite to fluorcalciobritholite for- med only at 350 °C and 200-400 MPa. The enrichment of the apatite in REE is related to the coupled substitutions of (1) REE3+ + Si4+ = Ca2+ + P5+ and (2) REE3+ + Na+ = 2Ca2+ (Pan and Fleet, 2002). Concentrations of Si (0.7-5.8 wt % SiO2; 0.066-0.589 cations per formula unit, c.p.f.u.) and Na (3.7-4.7 wt % Na2O; 0.723-0.920 c.p.f.u.) are too low to compensate for significant substitution of Y+REE (29.6- 37.6 wt % (Y+REE)2O3; 1.083-1.408 c.p.f.u.; Table 4). This phenomenon can be related to the experimental envi- ronment in the capsule that does not completely repl icate natural mineral reactions. The simplified reaction, docu- menting monazite alteration and subsequent REE enrich- ment in apatite, can be proposed according to Giere and So- rensen (2004): 3LREEPO4 + 3SiO2 + 7CaO + (F2, H2O) = monazite quartz in plagioclase in fluid Ca5(PO4)3 (F, OH) + Ca2LREE3(SiO4)3(F, OH) apatite britholite molecule in apatite The altered monazite showed porous textures related to partial dissolution. The pores showing preferred orientation along rims (Fig. 3A) or across whole grains (Figs 3C, D, 4) most likely developed owing to alteration, mediated by ag- gres t ive F-rich fluid peneirating monazite structure. The elongated pores show an orientation that probably is related to crystallographic parameters. This type of monazite alter- ation is unknown from previous experiments or in nature. Previous experiments by several authors utilized monazite from a heavy-mineral sand deposit, located in Clevel and County, North Carolina (Hetherington et al., 2010; Budzyń et al., 2011; Harlov et al., 2011; Williams et al., 2011). The experiments with the North Carolina monazite in the pres- ence of a sihcate assemblage simüar to that of the present study and Na2Si2O5 + H2O fluid run under P-T conditions of 450-500 °C and 450-610 MPa resulted in the develop- ment of patchy zoning related to a fluid-aided coupled dis- solution-reprecipitation process (Budzyń et al., 2011; Wil- liams et al., 2011). The altered domains in the North Caro- lina monazite were depleted in Th, U and Pb with respect to the unaltered patches, representing the composition of the starting monazite. Here, patchy zonmg also developed in the altered Burnet monazite. The altered domains were de- pleted in Y, Th, U, Pb, and Ca, with subsequent enrichment in LREE (Table 2; Fig. 5). The plots of formula proportions REE + P + Y vs. Th + U + Si indicated that both the cheralite and huttonite substitutions operated in the original Burnet monazite and the unalt ered domains of monazite from ex- periments (Fig. 5). The huttonite substitution dominated over the cheralite substitution in the altered monazite do t mains. Although similarities in compositional alteration be- tween the North Carolina monazite in previous experiments (Budzyń et al., 2011; Williams et al., 2011), and the Burnet monazite in this study, the formation porosity showing pre- ferred orientation in the Burnet monazite is a new type of al- teration. Seydoux-Guillaume et al. (2012) showed that radi- ation-damage may facilitate the fluid penetration of mona- zite, resulting in the remobilization of elements (such as Th, U, Pb) during hydrothermal alteration at temperatures be- low 320 °C. Here, a high Th concentration (9.4-17.0 wt % ThO2) and an old age of ca. 1072 Ma may indicate that the Burnet monazite can be affected by radiation damage. Al- though analyses of the monazite prior to experiments yiel- ded a uniform age with no Th-U-Pb disturbance in the com- positional domains, the presence of the metamict sites in the monazite structure cannot be excluded, as evidence of radi- ation damage was constrained and limhed to isotated na- nnometer-sized domains in the structure (Black et al., 1984; Meldrum et al., 1998; Seydoux-Guillaume et al., 2002b, 2003, 2004, 2007, 2012; Nasdala et al., 2010). Such grains may be more susceptible to preferentially oriented dissolu- tion of monazite during fluid-aided experimental alteration. Although there was high availability of Ca from CaF2 and of P from monazite, REE-enriched apatite to fluorcal- ciobritholite was not the main phase incorporating the Y, REE, Th, and U released during the alteration of monazite in the presence of Na2Si2O5 + H2O. Th, U and REE, were preferentially incorporated into the REE-rich steacyite, which played an important role during the experimental al- teration of the monazite. The REE-rich steacyite commonly overgrew the altered monazite, but also filled the pore spa- ces in alt ered areas of the monazite. The presence of the REE-rich steacyite inclusions in monazite indicates the fluid-aided transport of Si, Ca, Na, K and other elements into the monazite. The REE-rich steacyite, forming outside of the monazite in the capsule charge, either as intergrowths with monazite or as individual grains, indicates high Th, U and REE mobility, most likely induced by the presence of F in the fluid. The increasing contents of REE and Ca, accom- panying increasing experimental P-T conditions, correlate with a decrease in Th and Na, according to the coupled sub- stitution of REE3+ + Ca2+ = Th4+ + Na+ (Vilalva and Vlach, 2010). The presence of individual crystals of REE-enriched apatite to fluorcalciobritholite indicate transport of the Y+REE released from monazite, probably in fluoride com- plexes, as documented in previous studies on the mobility of Y + REE (Wood, 1990; Pan and Fleet, 1996) or hydroxide complexes (Haas et al., 1995; Poitrasson et al., 2004). A high alkalinity of the fluid induced mobilization of Th (cf. Ermolaeva et al., 2007), promoting further crystallization of individual crystals of REE-rich steacyite. The previous experiments under conditions of 450- 500 °C and 450-610 MPa, using simitar mineral composi- tion and Na2Si2O5 + H2O fluid, documented the alteration of monazite with the format ion of a fluorapatite-britholite solid solution and turkestanite, a Th-Ca-Na-K silicate with a similar composition to the REE-rich steacyite of this study, but lower totals indicating the presence of water component (Budzyń et al., 2011). The following reaction presenting the distribution of REE and Th between phosphates and silti cates was proposed (Budzyń et al., 2011): 416 B. BUDZYŃ ET AL. 3(REE, Th)PO4 + NaAlSi3O8 + 8SiO2 + 3Ca2+ + H2O = monazite albite quartz fluid-I = Ca2REE3(PO4, SiO4)3(F, OH) + fluorapatite-britholite Th(Ca, Na)2(K1-x,Dx)[Si8O20] nH2O + fluid-II turkestanite The REE-entiched apatite to fluorcalciobritholite and the REE-rich steacyite formed in this study in accordance with equivalent reactions involving monazite alteration. In nature, the formation of steacyite or turkestanite replacmg monazite is probably not documented. Steacyite and turkes- tanite are known from only several alkaline complexes (e.g., Pautov et al., 1997, 2004; Kabalov et al., 1998; Petersen et al., 1999). In the peralkaline granites of the Morro Redondo Complex in south Brasil, the crystallization of turkestanite, associated britholite and an unnamed (Y-REE)-hydrated sil- icate was attributed to a post-magmatic stage at tempera- tures of ca. 450 °C (Vilalva and Vlach, 2010). The current experimental study, partially replicating natural observa- tions, adds important new data to our knowledge of the par- titioning of Th, U and REE between phosphates and silica- tes under conditions of 250-350 °C, replicating post-mag- matic, low-temperature hydrothermal processes in a high- alkali- and alkaline environment. Implications for the natural occurrence of monazite and Th-U-Pb geo chron ology The experimental results add important information to the limited knowledge on the stability of monazite in low-temperature processes. The alteration of monazite and the formation of Th-silicates was also recognized in hydro- thermally altered granitic rocks in the Precambrian crystal- line basement of the Athabasca Basin, Saskatchewan, Can- ada (Hecht and Cuney, 2000). Poitrasson et al. (2000) also reported alteration in hydrothermally altered Palaeozoic granites in the Massif Central (France), Cornwall (England) and the Lake District (England) under temperature conditions of ca. 260-340 °C, affecting monazite via coupled dissolu- tion-reprecipitation, resulting in cationic substitutions and se- lective Th depletion. The alteration of detrital igneous mona- zite under mid-greenschist facies conditions (ca. 350 °C), re- sulted in replacement by low-Th metamorphic monazite, apa- tite and ThSiO4 in sandstones with a low-Ca bulk composi- tion, or all anite in moderate- to high-Ca sandstones in the Witwatersrand basin, South Africa (Rasmussen and Muh- ling, 2009). Also, Rasmussen and Muhling (2007) reported monazite with high-Th cores and low-Th rims with ThSiO4 inclusions in metasedimentary rocks from the Paleoprote- rozoic Stirling Range Formation (southwestern Australia). The presence of low-Th, inclusion-rich rims was interpreted as being related to the replacement of older monazite via a dissolution and reprecipitation process under conditions of low-grade metamorphism (<400 °C; Rasmussen and Muh- ling, 2007). The results of the study reported here show that monazite remains stable in experiments replicating low- grade metamorphic conditions in high bulk Ca composition of the capsule charge (runs with 2M Ca(OH)2 fluid). On the other hand, the experiments with elevated bulk contents of Na and Ca, related to the presence of Na2Si2O5 + H2O and CaF2 in excess, respect ively, have shown that monazite is unstable in this kind of bulk composition. Remobilized Th and U were incorporated in a newly formed REE-rich stea- cyite, The Th-rich phase that was apparently stable in the al- kaline system used, in contrast to ThSiO4 formed during low- temperature monazite alteration in nature, mentioned above. It should be also noted that compositional alteration during the experiments included LREE-enrichment and HREE-de- pletion of the altered domains in monazite (Table 2). Previous experiments showed that the fluid-mediated coupled dissolution-reprecipitation process may result in set ective remobilization of Th, U and Pb in monazite, sig- nificantly affecting the age record in high-grade rocks (Teu- fel and Heinrich, 1997; Seudoux-Guillaume et al., 2002a; Harlov et al., 2007, 2011; Harlov and Hetherington 2010; Hetherington et al., 2010). The essential “dating” of experi- mental products from runs under P-T conditions of 450 MPa and 450 °C over 16 days showed that altered zones in patchy monazite (the starting monazite was homogeneous) yielded an “age” of nearly zero, while unalt ered domains maintain the age of ca. 350 Ma of the North Caroline mona- zite used in the experiments (Wiltiams et al., 2011). The study by the present authors used a simüar starting mineral assemblage in the presence of Na2Si2O5 + H2O fluid, as used in Wiltiams et al. (2011). The recorded Th-U-total Pb age disturbance in the altered domains did not result in the com- plete retetting of the Th-U-Pb clock, but rej uvenated the “ages” of monazite internal domains from 1072 ± 2.8 Ma to 375-771 Ma (250 °C, 200 MPa), 82-253 Ma (350 °C, 200 MPa), and 95-635 Ma (350 °C, 400 MPa). The possibihty cannot be excluded that low-temperature metamorphic con- ditions are too low to reset the monazite clock. There are sev- eral factors that may control and limit the alteration mecha- nism. It should be noted, that the Au capsule forms a closed system of solids and fluid and fluid reactivity decreases with time during the experiment. The low P-T conditions were compensated by durations of 40 and 20 days in 250 °C and 350 °C runs, respectively, compared to the 16 days used in Williams et al. (2011). The “age” record, reflecting a distur- bance of the Th-U-Pb system in the altered domains (Fig. 6C, F, I), is strictly re lated to the rate of remobilization of these elements. The mechanism of monazite alt eration via fluid-mediated coupled dissolution-reprecipitation in the experiments is probably limbed remobilization of the ele t ments. Therefore, a crucial factor most likely is the compo- sition of the Burnet monazite, containing 0.5-0.9 wt % PbO in contrast to the significantly lower amounts of 0.10-0.16 wt % PbO in the North Caroline monazite. The high Pb con- tent explains partial instead of complete removal of Pb in the altered domains of the Burnet monazite. Future experi- ments should expand the considerations of timmg to con- strain the effects of experiment duration on the remobiliza- tion of the elements in monazite struct ure under low-tem- perature conditions. The potentially altered compositional domains of mo- nazite may be reflected in the dark patches in high-contrast BSE imaging, the presence of secondary minerals inclu- sions or the poroshy developed. Assuming a total removal of Pb, monazite can provide an age record of the metaso- STABILITY OF MONAZITE AND DISTURBANCE OF THE Th-U-Pb SYSTEM 417 matic event (Williams et al., 2011). However, the low-tem- perature alt eration may result in the disturbance of the Th- U-Pb system of monazite without complete re setting the ages, as shown in the present study. For instance, the post- magmatic alt eration of granitic rocks is very common and avoiding altered domains may provide accurate geochronol- ogical data, as in the case of the Stolpen granite with recog- nized postmagmatic monazite alteration (Lisowiec et al., 2013), where further study involving monazite datmg pro- vided the age of the magmatic event and the emplacement of the granitoid pluton (Lisowiec et al., 2014). The recognition of the monazite domains affected by fluid-mediated alt er- ation is crucial in applications of monazite geochronology. CON CLU SIONS This experimental study provides important data for the understanding and interpretation of metasomatic processes in nature. 1) Monazite is stable under conditions of 250-350 °C and 200-400 MPa in the presence of 2M Ca(OH)2 fluid. Lack of altanite in the experimental products is retated to the monazite-to-allanite transition at higher P-T conditions. 2) A system high in Na-Ca with a Na2Si2O5 + H2O fluid promotes monazite alteration. Released REE, Th and U are incorporated in newly formed REE-enriched apatite, fluorcalciobritholite and REE-rich steacyite. The predomu nance of the REE-rich steacyite in the products indicates preferential partitioning of Th and REE in silicates over phosphates during processes at 250-350 °C. 3) Partial removal of Pb from the monazite used in the experiments resulted in the disturbance of the Th-U-Pb sys- tem without complete resetting of the monazite clock. Mo- nazite geochronological data from natural samples should be interpreted with caution. This is also true for the correla- tion of compositional, text ural and age data to understand the effects of the recorded processes on monazite composi- tion and potentially the ages recorded. Ac knowl edge ments The analyses of the starttng minerals were financially sup t ported by the National Science Centre Retearch Grant Number 2011/01/D/ST10/04588. This work was supported by the ING PAN Research Funds (Proj ect “EXP”). B. Budzyń thanks W. Heinrich and D. E. Harlov for access to the experimental laboratories of the Deutsche GeoForschungsZentrum, Potsdam, Germany. I. Holicky and V. Kollarova are thanked for their assistance during electron microprobe analyses. The Burnet monazite was provided by M. J. Jercinovic and M. L. Williams. This article greatly benefited from reviews by I. Broska and P. Uher, from editorial work by M. Gra- dziński and F. Simpson, and from discussions with M. 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Average results of the electron microprobe analyzes of labradorite, albite and K-feldspar Sample T [°C] P [MPa] duration n SiO2 Al2O3 MgO CaO FeO SrO BaO Na2O K2O Total [days] Starting labradorite 14 52.54 29.10 0.09 12.14 0.34 0.11 <0.01 4.34 0.26 98.92 0.74 0.52 0.02 0.10 0.03 0.05 0.13 0.01 M12C-04 250 200 40 5 53.60 29.26 0.10 12.21 0.35 0.13 <0.01 4.31 0.27 100.23 0.26 0.13 0.02 0.06 0.01 0.03 0.04 0.02 M12C-05 350 200 40 5 52.21 28.91 0.08 12.28 0.34 0.11 0.03 4.17 0.27 98.39 0.11 0.13 0.02 0.05 0.04 0.02 0.00 0.07 0.01 M12C-15 350 400 20 2 53.52 29.62 0.10 12.12 0.30 0.13 0.02 4.27 0.20 100.29 0.42 0.27 0.01 0.07 0.01 0.03 0.01 0.07 0.07 Starting albite 10 68.77 19.74 <0.01 0.02 <0.01 0.03 <0.01 11.77 0.05 100.40 0.49 0.21 0.03 0.04 0.19 0.02 M12N-04 250 200 40 5 69.57 19.41 <0.01 0.03 0.03 <0.01 <0.01 11.43 0.07 100.54 0.30 0.13 0.01 0.01 0.15 0.01 M12N-05 350 200 40 4 68.14 19.25 <0.01 0.05 0.06 <0.01 <0.01 11.29 0.07 98.86 0.26 0.09 0.02 0.04 0.06 0.01 M12N-15 350 400 20 5 65.09 18.81 <0.01 <0.01 0.14 0.15 0.94 1.54 13.31 100.00 0.39 0.11 0.01 0.07 0.04 0.03 0.72 Starting K-feldspar 23 64.10 18.72 <0.01 <0.01 0.13 0.16 0.94 1.56 13.80 99.43 0.62 0.20 0.03 0.06 0.05 0.07 0.29 M12C-04 250 200 40 5 64.91 18.51 <0.01 0.02 0.17 <0.01 0.97 1.53 14.07 100.17 0.27 0.10 0.00 0.02 0.02 0.04 0.07 M12C-05 350 200 40 5 60.51 20.91 <0.01 6.08 0.19 0.15 0.97 1.99 10.60 101.40 5.54 5.10 8.57 0.10 0.03 0.02 1.17 6.89 M12C-15 350 400 20 10 65.32 18.83 <0.01 <0.01 0.14 0.17 0.95 1.50 13.28 100.21 0.37 0.07 0.03 0.04 0.04 0.07 0.73 M12N-04 11 64.59 18.72 <0.01 <0.01 0.14 0.13 0.95 1.55 13.86 99.94 0.33 0.23 0.02 0.06 0.04 0.04 0.24 M12N-04 2 68.98 19.08 <0.01 0.03 0.05 <0.01 <0.01 11.22 0.21 99.57 0.88 0.08 0.01 0.02 0.27 0.15 M12N-05 8 64.18 18.69 <0.01 <0.01 0.16 0.14 0.91 1.57 13.88 99.53 1.29 0.49 0.03 0.03 0.05 0.08 0.15 M12N-05 3 69.57 19.16 <0.01 <0.01 0.19 <0.01 <0.01 11.51 0.21 100.66 0.75 0.19 0.02 0.28 0.11 M12N-15 6 65.02 18.47 <0.01 0.20 0.17 0.07 0.51 1.32 14.39 100.13 1.34 0.55 0.40 0.09 0.06 0.46 0.37 0.58 M12N-15 4 69.28 19.42 <0.01 0.05 0.19 <0.01 <0.01 11.42 0.22 100.60 0.62 0.58 0.03 0.13 0.16 0.06 Comments: all values are given in wt %; italic - standard deviation. Appendix 2. Average results of the electron microprobe analyzes of biotite and muscovite T P dura¬ Sample [°C] [MPa] tion n SiO2 TiO2 Al2O3 Cr2O3 MgO CaO MnO FeO NiO Na2O K2O F Cl Total [days] Starting biotite 24 34.77 3.75 18.56 0.06 9.23 <0.01 0.03 16.95 0.02 0.08 9.16 0.20 <0.01 92.84 0.45 0.70 0.62 0.04 0.56 0.02 0.53 0.02 0.02 0.09 0.11 M12C-04 250 200 40 5 35.47 4.36 18.48 0.07 8.91 0.05 0.05 17.15 <0.01 0.08 9.42 0.11 <0.01 94.11 0.16 0.34 0.22 0.01 0.51 0.05 0.03 0.69 0.03 0.12 0.09 M12C-05 350 200 40 5 34.88 4.44 17.99 0.07 8.77 0.05 0.05 17.51 <0.01 0.09 9.39 0.09 <0.01 93.28 0.24 0.55 0.38 0.01 0.30 0.02 0.01 0.93 0.04 0.09 0.07 STABILITY OF MONAZITE AND DISTURBANCE OF THE Th-U-Pb SYSTEM 421 T P dura¬ Sample [°C] [MPa] tion n SiO2 TiO2 Al2O3 Cr2O3 MgO CaO MnO FeO NiO Na2O K2O F Cl Total [days] M12C-15 350 400 20 5 35.44 4.65 18.39 0.05 8.62 0.02 0.04 17.00 0.03 0.09 9.32 0.16 <0.01 93.80 0.52 0.12 0.28 0.01 0.28 0.02 0.02 0.43 0.02 0.01 0.09 0.10 M12N-04 250 200 40 5 35.64 4.54 18.39 0.06 9.01 0.03 0.06 17.63 0.02 0.10 9.46 0.17 <0.01 95.03 0.41 0.15 0.42 0.03 0.35 0.03 0.02 0.66 0.02 0.02 0.13 0.07 M12N-05 350 200 40 5 34.82 4.54 17.88 0.06 8.96 0.02 0.05 17.69 0.02 0.12 9.56 0.12 <0.01 93.79 0.41 0.37 0.42 0.03 0.38 0.02 0.02 0.28 0.02 0.03 0.07 0.05 M12N-15 350 400 20 6 36.04 4.16 18.47 0.03 8.87 0.03 0.03 16.89 0.02 0.24 9.29 0.17 <0.01 94.25 0.39 0.65 0.16 0.01 0.19 0.03 0.03 0.11 0.03 0.24 0.15 0.15 Starting muscovite 12 46.56 0.17 34.10 <0.01 0.91 <0.01 0.07 2.46 <0.01 0.65 9.65 <0.01 <0.01 94.58 0.53 0.06 0.75 0.27 0.03 0.35 0.09 0.19 M12C-04 250 200 40 4 45.58 0.18 33.37 <0.01 0.99 0.04 0.07 2.57 0.02 0.69 10.06 <0.01 <0.01 93.57 0.12 0.06 0.27 0.12 0.01 0.04 0.08 0.02 0.05 0.07 M12C-05 350 200 40 5 45.23 0.15 33.41 0.02 1.01 0.04 0.07 2.82 <0.01 0.66 9.95 <0.01 <0.01 93.37 0.21 0.03 0.15 0.02 0.13 0.03 0.04 0.08 0.04 0.16 M12C-15 350 400 20 5 49.14 0.15 35.52 <0.01 1.02 0.04 0.04 2.66 <0.01 0.50 8.80 <0.01 <0.01 97.86 0.36 0.03 0.10 0.08 0.03 0.03 0.11 0.13 0.17 M12N-04 250 200 40 5 45.76 0.15 33.49 <0.01 1.02 0.07 0.05 2.66 <0.01 0.77 10.06 <0.01 <0.01 94.03 0.76 0.04 0.50 0.06 0.09 0.06 0.07 0.11 0.13 M12N-05 350 200 40 5 45.28 0.17 32.90 <0.01 1.16 0.03 0.06 2.89 <0.01 0.71 10.03 <0.01 <0.01 93.24 0.13 0.03 0.26 0.17 0.01 0.02 0.23 0.02 0.10 M12N-15 350 400 20 5 48.71 0.14 35.03 0.03 1.07 0.03 0.07 2.68 0.02 0.75 8.84 0.04 <0.01 97.39 0.40 0.05 0.69 0.02 0.02 0.03 0.03 0.07 0.02 0.10 0.30 0.04 Comments: all values are given in wt %; Total values are corrected for O = F; Italic - standard deviation. Appendix. 3. Results of electron microprobe analyzes of monazite presenting contents of Th, U, Pb and Y, calculated Th* and monazite Th-U-total Pb ages Analysis Th [wt %] ±2c U [wt %] ±2c Pb [wt %] ±2c Y [wt %] Th* [wt %] Age [Ma] ±1c Unaltered; Average age ±2c = 1095±4.6 Ma; MSWD = 1.74 M12C-04_1-1 10.0927 0.0447 0.2972 0.0127 0.5537 0.0075 0.6776 11.12 1093 20.7 M12C-04_1-2 10.5048 0.0458 0.3232 0.0130 0.5711 0.0076 0.7084 11.62 1079 20.0 M12C-04_1-3 10.3333 0.0454 0.3165 0.0129 0.5700 0.0076 0.6749 11.43 1095 20.3 M12C-04_1-4 10.3311 0.0454 0.3067 0.0129 0.5664 0.0076 0.6994 11.39 1092 20.4 M12C-04_1-5 10.3897 0.0455 0.3119 0.0129 0.5676 0.0076 0.6924 11.47 1087 20.2 M12C-04_2-1 8.9550 0.0421 0.2913 0.0127 0.4886 0.0073 0.4947 9.96 1078 22.2 M12C-04_2-2 8.8491 0.0420 0.2832 0.0127 0.4875 0.0073 0.4729 9.83 1089 22.6 M12C-04_2-3 8.9498 0.0423 0.2831 0.0127 0.4857 0.0073 0.4938 9.93 1075 22.3 M12C-04_2-4 8.8935 0.0420 0.2867 0.0127 0.4891 0.0073 0.5073 9.89 1087 22.5 M12C-04_2-5 8.9411 0.0421 0.2870 0.0127 0.4932 0.0073 0.4885 9.93 1090 22.4 M12C-04_3-1 10.3160 0.0454 0.3178 0.0129 0.5642 0.0076 0.7428 11.42 1086 20.3 M12C-04_3-2 10.2674 0.0452 0.3242 0.0129 0.5648 0.0076 0.7427 11.39 1089 20.4 M12C-04_3-3 10.3746 0.0455 0.3264 0.0129 0.5688 0.0076 0.7428 11.50 1086 20.2 M12C-04_3-4 10.2349 0.0453 0.3076 0.0129 0.5755 0.0077 0.7681 11.30 1118 20.8 M12C-04_3-5 10.1098 0.0449 0.3137 0.0129 0.5705 0.0076 0.7459 11.20 1118 20.8 M12C-04_4-1 10.6589 0.0461 0.3135 0.0129 0.5974 0.0077 0.7368 11.75 1116 20.2 M12C-04_4-2 10.6597 0.0461 0.2919 0.0129 0.5946 0.0077 0.7392 11.67 1118 20.3 M12C-04_4-3 10.5469 0.0458 0.3048 0.0129 0.5858 0.0077 0.7347 11.60 1108 20.2 M12C-04_4-4 10.8378 0.0465 0.3104 0.0130 0.5959 0.0077 0.7344 11.91 1098 19.8 M12C-04_4-5 10.7369 0.0462 0.3131 0.0129 0.5867 0.0077 0.7259 11.82 1090 19.8 422 B. BUDZYŃ ET AL. Analysis Th [wt %] ±2c U [wt %] ±2c Pb [wt %] ±2c Y [wt %] Th* [wt %] Age [Ma] ±1c Unaltered; Average age ±2c = 1074±6.7 Ma; MSWD = 0.77 M12N-04_1-1 10.7791 0.0465 0.3255 0.0131 0.5794 0.0077 0.7640 11.90 1069 19.6 M12N-04_1-2 10.5843 0.0462 0.3201 0.0130 0.5742 0.0077 0.7256 11.69 1079 20.0 M12N-04_2-4 11.2180 0.0473 0.3199 0.0131 0.6013 0.0077 0.7114 12.32 1072 19.1 M12N-04_2-5 11.2229 0.0473 0.3347 0.0131 0.6080 0.0078 0.7245 12.38 1079 19.2 M12N-04_3-4 10.7010 0.0464 0.3176 0.0131 0.5796 0.0077 0.7374 11.80 1079 19.9 M12N-04C_1-5 11.2295 0.0957 0.3528 0.0133 0.6025 0.0076 0.9369 12.45 1064 20.8 M12N-04C_1-6 10.9688 0.0937 0.3504 0.0132 0.6011 0.0076 0.9409 12.18 1084 21.2 M12N-04C_1-7 11.0135 0.0942 0.3504 0.0133 0.6039 0.0077 0.9356 12.23 1085 21.3 M12N-04C_1-8 11.2003 0.0955 0.3489 0.0133 0.5973 0.0076 0.9212 12.40 1058 20.8 Altered M12N-04_2-1 3.3215 0.0268 0.0608 0.0115 0.0989 0.0057 0.1453 3.52 624 44.2 M12N-04_2-2 4.8266 0.0316 0.0817 0.0119 0.1254 0.0058 0.1902 5.10 547 30.8 M12N-04_2-3 4.5126 0.0307 0.0882 0.0117 0.1364 0.0059 0.1808 4.81 630 33.7 M12N-04_3-1 4.7766 0.0314 0.0895 0.0117 0.1295 0.0058 0.2104 5.07 568 31.1 M12N-04_3-2 4.6864 0.0312 0.1027 0.0118 0.1390 0.0059 0.2063 5.03 614 32.4 M12N-04_3-3 3.2830 0.0268 0.0529 0.0115 0.0580 0.0055 0.0876 3.46 375 41.0 M12N-04C_1-1 4.4495 0.0450 0.0368 0.0114 0.1594 0.0059 0.1826 4.57 771 38.0 M12N-04C_1-2 4.7467 0.0472 0.1101 0.0116 0.1517 0.0059 0.2568 5.11 658 33.0 M12N-04C_1-3 5.3955 0.0520 0.1379 0.0119 0.1910 0.0060 0.3431 5.86 722 30.3 M12N-04C_1-4 4.3014 0.0439 0.1036 0.0116 0.1476 0.0059 0.2202 4.65 704 36.6 Unaltered; Average age ±2c = 1100±4.8 Ma; MSWD = 0.63 M12C-05_1-1 10.3223 0.0454 0.3233 0.0129 0.5679 0.0076 0.8211 11.44 1090 20.3 M12C-05_1-2 10.3522 0.0455 0.3345 0.0130 0.5744 0.0077 0.8754 11.51 1096 20.3 M12C-05_1-3 10.2644 0.0453 0.3402 0.0130 0.5784 0.0077 0.8587 11.44 1110 20.5 M12C-05_1-4 10.3998 0.0457 0.3391 0.0131 0.5768 0.0077 0.8521 11.57 1094 20.2 M12C-05_1-5 10.2645 0.0453 0.3284 0.0131 0.5705 0.0077 0.8386 11.40 1099 20.6 M12C-05_2-1 10.2674 0.0452 0.3372 0.0129 0.5683 0.0076 0.8347 11.43 1091 20.3 M12C-05_2-2 10.3303 0.0455 0.3389 0.0131 0.5754 0.0077 0.8337 11.50 1098 20.4 M12C-05_2-3 10.3785 0.0455 0.3383 0.0130 0.5857 0.0077 0.8462 11.55 1113 20.5 M12C-05_2-4 10.2524 0.0453 0.3370 0.0130 0.5781 0.0077 0.8454 11.42 1111 20.6 M12C-05_3-1 8.0731 0.0401 0.2386 0.0125 0.4469 0.0071 0.3517 8.90 1102 24.6 M12C-05_3-2 8.1621 0.0403 0.2412 0.0125 0.4488 0.0071 0.3396 9.00 1095 24.1 M12C-05_3-3 8.1009 0.0401 0.2443 0.0125 0.4482 0.0071 0.3595 8.95 1100 24.4 M12C-05_3-4 8.1499 0.0403 0.2405 0.0125 0.4557 0.0071 0.3334 8.98 1113 24.4 M12C-05_3-5 8.1400 0.0401 0.2421 0.0124 0.4505 0.0071 0.3418 8.98 1102 24.2 M12C-05_4-1 10.7184 0.0463 0.3194 0.0130 0.5830 0.0077 0.7313 11.82 1083 19.8 M12C-05_4-2 10.6644 0.0461 0.3196 0.0129 0.5950 0.0077 0.7110 11.77 1109 20.1 M12C-05_4-3 10.6991 0.0461 0.3133 0.0129 0.5913 0.0077 0.7292 11.78 1102 19.9 M12C-05_4-4 10.5292 0.0458 0.3159 0.0129 0.5828 0.0077 0.7221 11.62 1101 20.1 M12C-05_4-5 10.7632 0.0463 0.3046 0.0129 0.5894 0.0077 0.7183 11.82 1095 20.0 Unaltered; Average age ±2c = 1081±7.3 Ma; MSWD = 0.68 M12N-05_1-4 11.2156 0.0474 0.3425 0.0132 0.6030 0.0078 0.6951 12.40 1069 19.1 M12N-05_1-5 11.0509 0.0469 0.3392 0.0131 0.5977 0.0077 0.6945 12.22 1074 19.3 M12N-05_1-6 11.0562 0.0470 0.3128 0.0131 0.5998 0.0077 0.7281 12.14 1085 19.5 M12N-05_1-7 11.0936 0.0471 0.3309 0.0131 0.6075 0.0078 0.7647 12.24 1090 19.5 M12N-05C_1-6 12.7771 0.1074 0.3919 0.0136 0.6968 0.0080 1.2010 14.13 1083 19.5 M12N-05C_1-7 12.7707 0.1073 0.3903 0.0135 0.6995 0.0080 1.2014 14.12 1088 19.5 M12N-05C_1-8 12.8111 0.1076 0.4007 0.0136 0.6951 0.0080 1.2099 14.20 1076 19.4 Altered M12N-05_1-1 3.2555 0.0266 0.0424 0.0114 0.0144 0.0054 0.0580 3.39 96 37.3 M12N-05_1-2 5.2426 0.0327 0.0714 0.0117 0.0617 0.0056 0.1065 5.47 253 25.3 STABILITY OF MONAZITE AND DISTURBANCE OF THE Th-U-Pb SYSTEM 423 Analysis Th [wt %] ±2c U [wt %] ±2c Pb [wt %] ±2c Y [wt %] Th* [wt %] Age [Ma] ±1c M12N-05_1-3 6.8752 0.0371 0.0536 0.0117 0.0268 0.0055 0.1216 7.05 86 18.1 M12N-05C_1-1 2.9899 0.0341 0.0393 0.0113 0.0141 0.0053 0.0424 3.12 102 40.4 M12N-05C_1-2 2.6944 0.0320 0.0360 0.0113 0.0102 0.0053 0.0570 2.81 82 44.4 M12N-05C_1-3 5.1182 0.0500 0.0498 0.0115 0.0249 0.0054 0.0616 5.28 106 24.3 M12N-05C_1-4 1.8673 0.0258 0.0169 0.0111 0.0153 0.0053 0.0382 1.92 179 67.0 M12N-05C_1-5 1.8951 0.0260 0.0419 0.0111 0.0180 0.0053 0.0562 2.03 199 63.8 Unaltered; Average age ±2c = 1088±5.0 Ma; MSWD = 1.05 M12C-15_1-1 10.9781 0.0469 0.3266 0.0131 0.5961 0.0077 0.7320 12.11 1081 19.5 M12C-15_1-2 10.8815 0.0468 0.3322 0.0132 0.5910 0.0077 0.7398 12.03 1079 19.6 M12C-15_1-3 11.1237 0.0473 0.3250 0.0132 0.5989 0.0078 0.7286 12.25 1074 19.4 M12C-15_2-1 10.5230 0.0460 0.3344 0.0132 0.5758 0.0077 0.7909 11.68 1083 20.1 M12C-15_2-2 10.6636 0.0463 0.3246 0.0132 0.5770 0.0077 0.8327 11.79 1076 19.9 M12C-15_1-1 10.9211 0.0933 0.3074 0.0129 0.6048 0.0076 0.7028 11.99 1107 21.7 M12C-15_1-2 10.7561 0.0921 0.4018 0.0127 0.5925 0.0075 0.6450 12.14 1072 20.9 M12C-15_1-3 10.7703 0.0923 0.4262 0.0126 0.6064 0.0077 0.5847 12.25 1088 21.0 M12C-15_2-1 8.2802 0.0737 0.2668 0.0126 0.4546 0.0071 0.3927 9.20 1085 25.5 M12C-15_2-2 8.2839 0.0737 0.2575 0.0126 0.4642 0.0071 0.3947 9.18 1110 25.8 M12C-15_2-3 8.3670 0.0743 0.2494 0.0126 0.4659 0.0071 0.3981 9.23 1108 25.7 M12C-15_3-1 10.5061 0.0904 0.4008 0.0129 0.5917 0.0076 0.8822 11.89 1093 21.5 M12C-15_3-3 10.5913 0.0911 0.3200 0.0131 0.5868 0.0076 0.8753 11.70 1101 22.1 M12C-15_4-1 9.5618 0.0833 0.2753 0.0127 0.5185 0.0073 0.6174 10.51 1083 23.3 M12C-15_4-2 9.3733 0.0818 0.2793 0.0127 0.5163 0.0073 0.6153 10.34 1096 23.6 M12C-15_4-3 9.4190 0.0822 0.2782 0.0127 0.5162 0.0073 0.6252 10.38 1092 23.7 M12C-15_5-1 10.4504 0.0899 0.3172 0.0131 0.5723 0.0075 0.8680 11.55 1088 22.1 M12C-15_5-2 10.3932 0.0895 0.3304 0.0131 0.5753 0.0075 0.8549 11.54 1095 22.1 M12C-15_5-3 10.3433 0.0891 0.3093 0.0129 0.5632 0.0075 0.8365 11.41 1084 22.1 M12C-15_5-2 10.3932 0.0895 0.3304 0.0131 0.5753 0.0075 0.8549 11.54 1095 22.1 M12C-15_5-3 10.3433 0.0891 0.3093 0.0129 0.5632 0.0075 0.8365 11.41 1084 22.1 Unaltered; Average age ±2c = 1084±7.9 Ma; MSWD = 1.89 M12N-15_1-2 8.8713 0.0421 0.2730 0.0127 0.4799 0.0073 1.1476 9.81 1074 22.6 M12N-15_1-3 8.7326 0.0419 0.2633 0.0127 0.4697 0.0073 1.1600 9.64 1070 22.9 M12N-15_2-5 8.6165 0.0415 0.2749 0.0128 0.4829 0.0073 0.3962 9.57 1108 23.4 M12N-15_2-6 8.5621 0.0413 0.2795 0.0127 0.4830 0.0073 0.3985 9.53 1112 23.4 M12N-15C_2-5 8.6945 0.0768 0.2697 0.0127 0.4666 0.0071 0.5164 9.63 1065 24.5 M12N-15C_2-6 8.7279 0.0771 0.2660 0.0127 0.4768 0.0071 0.5245 9.65 1085 24.7 M12N-15C_2-7 8.8968 0.0783 0.2844 0.0128 0.4831 0.0071 0.4128 9.88 1074 24.1 M12N-15C_2-8 8.7597 0.0773 0.2793 0.0127 0.4804 0.0071 0.4196 9.73 1085 24.5 M12N-15C_2-9 8.7879 0.0775 0.2779 0.0127 0.4812 0.0071 0.4068 9.75 1084 24.5 Altered M12N-15_1-1 3.1034 0.0263 0.0350 0.0114 0.0165 0.0053 0.0665 3.22 116 39.1 M12N-15_2-1 4.0639 0.0293 0.0659 0.0116 0.0677 0.0055 0.0883 4.28 354 33.0 M12N-15_2-2 3.6300 0.0279 0.0428 0.0115 0.0431 0.0055 0.0697 3.77 256 35.9 M12N-15_2-3 4.8154 0.0315 0.0885 0.0117 0.1461 0.0058 0.1425 5.11 635 31.5 M12N-15_2-4 4.1750 0.0297 0.0625 0.0117 0.0841 0.0057 0.1063 4.38 428 33.8 M12N-15C_1-1 2.9319 0.0336 0.0300 0.0112 0.0179 0.0053 0.0677 3.03 133 42.0 M12N-15C_2-1 1.3111 0.0217 0.0229 0.0111 0.0059 0.0053 0.0618 1.38 95 89.4 M12N-15C_2-2 2.1793 0.0281 0.0303 0.0112 0.0157 0.0053 0.0499 2.28 155 56.2 M12N-15C_2-3 3.2051 0.0357 0.0529 0.0113 0.0732 0.0055 0.1215 3.38 483 44.0 M12N-15C_2-4 3.3722 0.0370 0.0467 0.0113 0.0467 0.0055 0.0942 3.52 297 39.3 Burnet monazite; Average age ±2c = 1072±2.8 Ma; MSWD = 1.89 MX-12SM_1-1 9.0852 0.0426 0.2961 0.0129 0.4895 0.0073 0.5196 10.11 1064 22.1 MX-12SM_1-2 9.1033 0.0426 0.2864 0.0129 0.4856 0.0073 0.4937 10.09 1058 22.0 424 B. BUDZYŃ ET AL. Analysis Th [wt %] ±2 o U [wt %] ±2 o Pb [wt %] ±2 o Y [wt %] Th* [wt %] Age [Ma] ±1 o MX-12SM_1-3 9.0960 0.0429 0.2878 0.0129 0.4922 0.0074 0.5200 10.09 1072 22.4 MX-12SM_1-4 9.1297 0.0428 0.2906 0.0129 0.4840 0.0073 0.5108 10.13 1050 22.0 MX-12SM_1-5 8.9866 0.0423 0.2827 0.0128 0.4787 0.0073 0.5100 9.96 1056 22.2 MX-12SM_1-6 9.0441 0.0425 0.2983 0.0129 0.4813 0.0073 0.5049 10.07 1050 22.1 MX-12SM_1-7 9.1058 0.0421 0.2886 0.0127 0.4920 0.0073 0.5099 10.10 1070 21.9 MX-12SM_2-1 9.4617 0.0430 0.2944 0.0128 0.5104 0.0073 0.6375 10.48 1070 21.3 MX-12SM_2-2 9.5737 0.0435 0.3045 0.0129 0.5191 0.0075 0.6169 10.63 1073 21.4 MX-12SM_2-3 9.5058 0.0435 0.2958 0.0129 0.5135 0.0075 0.6158 10.53 1072 21.6 MX-12SM_2-4 9.4199 0.0436 0.2938 0.0129 0.5126 0.0075 0.6431 10.44 1079 21.8 MX-12SM_2-5 9.5577 0.0439 0.3050 0.0129 0.5191 0.0075 0.6219 10.61 1075 21.5 MX-12SM_2-6 9.5268 0.0438 0.3073 0.0130 0.5127 0.0075 0.6236 10.59 1064 21.5 MX-12SM_3-1 9.0498 0.0427 0.2786 0.0129 0.4886 0.0073 0.5272 10.01 1072 22.4 MX-12SM_3-2 8.9896 0.0425 0.2871 0.0129 0.4876 0.0073 0.5120 9.98 1073 22.4 MX-12SM_3-3 8.9779 0.0423 0.2865 0.0127 0.4793 0.0073 0.5026 9.97 1057 22.2 MX-12SM_3-4 9.0614 0.0426 0.2822 0.0129 0.4854 0.0073 0.5317 10.04 1063 22.3 MX-12SM_3-5 8.9357 0.0423 0.2925 0.0128 0.4832 0.0073 0.5042 9.95 1067 22.4 MX-12SM_3-6 9.0728 0.0426 0.2983 0.0128 0.4964 0.0073 0.5058 10.10 1079 22.2 MX-12SM_4-1 11.1243 0.0473 0.3267 0.0132 0.6038 0.0079 0.7830 12.25 1082 19.5 MX-12SM_4-2 11.1909 0.0469 0.3301 0.0130 0.5990 0.0077 0.7968 12.33 1067 19.0 MX-12SM_4-3 11.1015 0.0466 0.3388 0.0130 0.5983 0.0077 0.7955 12.27 1071 19.1 MX-12SM_4-4 10.9403 0.0462 0.3326 0.0129 0.5849 0.0077 0.8133 12.09 1063 19.2 MX-12SM_4-5 11.1425 0.0472 0.3409 0.0131 0.5885 0.0077 0.7810 12.32 1050 19.0 MX-12SM_4-6 11.0763 0.0471 0.3325 0.0131 0.5917 0.0078 0.7758 12.22 1064 19.3 MX-12SM_5-1 14.8997 0.0551 0.4608 0.0140 0.7964 0.0087 1.2926 16.49 1061 15.9 MX-12SM_5-2 14.5576 0.0545 0.4555 0.0139 0.7970 0.0087 1.2307 16.13 1085 16.3 MX-12SM_5-3 14.3424 0.0543 0.4397 0.0139 0.7924 0.0087 1.2199 15.87 1097 16.6 MX-12SM_5-4 14.2808 0.0541 0.4504 0.0139 0.7816 0.0086 1.2333 15.84 1084 16.5 MX-12SM_5-5 14.3494 0.0542 0.4500 0.0139 0.7906 0.0087 1.2467 15.91 1091 16.5 MX-12SM_5-6 14.4524 0.0543 0.4222 0.0138 0.7840 0.0087 1.2459 15.91 1082 16.5 MX-12SM_6-1 11.4614 0.0481 0.3704 0.0134 0.6164 0.0079 0.9078 12.74 1063 18.9 MX-12SM_6-2 11.2802 0.0477 0.3655 0.0133 0.6107 0.0079 0.9075 12.54 1070 19.1 MX-12SM_6-3 11.2067 0.0475 0.3562 0.0133 0.6022 0.0079 0.9110 12.44 1064 19.2 MX-12SM_6-4 11.4488 0.0480 0.3937 0.0134 0.6170 0.0079 0.9365 12.81 1059 18.8 MX-12SM_6-5 11.4426 0.0479 0.3723 0.0133 0.6226 0.0079 0.9138 12.73 1075 18.9 MX-12SM_6-6 11.4669 0.0474 0.3776 0.0131 0.6141 0.0078 0.9038 12.77 1057 18.5 MX-12SM_7-1 8.2589 0.0407 0.2409 0.0126 0.4470 0.0071 0.3600 9.09 1080 24.0 MX-12SM_7-2 8.2650 0.0405 0.2555 0.0126 0.4480 0.0071 0.3561 9.15 1076 23.8 MX-12SM_7-3 8.2872 0.0406 0.2559 0.0127 0.4488 0.0071 0.3544 9.17 1075 23.8 MX-12SM_7-4 8.3101 0.0402 0.2573 0.0125 0.4449 0.0070 0.3573 9.20 1063 23.2 MX-12SM_7-5 8.3099 0.0407 0.2402 0.0126 0.4462 0.0071 0.3702 9.14 1072 23.8 MX-12SM_7-6 8.2886 0.0407 0.2477 0.0126 0.4491 0.0071 0.3712 9.14 1079 23.8 BrtMnz-2 10.6912 0.0463 0.3515 0.0132 0.5825 0.0077 0.8676 11.91 1075 19.8 BrtMnz-3 10.6000 0.0460 0.3434 0.0131 0.5724 0.0077 0.8421 11.79 1067 19.8 BrtMnz-4 10.8079 0.0465 0.3509 0.0132 0.5875 0.0077 0.8702 12.02 1074 19.6 BrtMnz-5 10.5602 0.0459 0.3224 0.0130 0.5730 0.0077 0.8091 11.67 1078 20.0 BrtMnz-6 10.4798 0.0457 0.3283 0.0131 0.5673 0.0077 0.7944 11.61 1073 20.1 BrtMnz-7 10.3819 0.0458 0.3376 0.0131 0.5614 0.0077 0.7601 11.55 1068 20.2 BrtMnz-8 10.2777 0.0453 0.3186 0.0130 0.5607 0.0076 0.7907 11.38 1082 20.4 BrtMnz-9 10.1626 0.0453 0.3230 0.0131 0.5571 0.0077 0.7735 11.28 1085 20.7 BrtMnz-10 10.1576 0.0451 0.3357 0.0131 0.5627 0.0077 0.7841 11.32 1092 20.7 BrtMnz-11 10.0710 0.0450 0.3432 0.0125 0.5497 0.0076 0.6973 11.26 1073 20.4