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The stability of xenotime in high Ca and Ca-Na systems, under experimental conditions of 250–350°C and 200–400 MPa : the implications for fluid-mediated low-temperature processes in granitic rocks

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Budzyń B. , Kozub-Budzyń G. A.

Geological Quarterly

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2015

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tom Vol. 59, No. 2

316–324

EN

he stability of xenotime was tested by experiments in the presence of a silicate mineral assemblage and two different fluids, 2M Ca(OH)2 or Na2Si2O5 + H2O, under P-T conditions of 200-400 MPa and 250-350°C. The xenotime was stable in runs with 2M Ca(OH)2, replicating the low-temperature metasomatic alterations of granitic rocks, except in experiment at 350°C and 400 MPa, where some (Y,REE)-rich fluorapatite formed. Experiments with Na2Si2O5 + H2O resulted in significant xenotime alteration and partial replacement by an unknown (Y,HREE)-rich silicate, and in the formation of minor amounts of (Y,REE)-rich fluorapatite. The latter indicate preferential partitioning of Y and REE into silicates over phosphates during low-temperature, metasomatic processes in a high Na-Ca system, similar to peralkaline granitic rocks.

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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)

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Budzyń B. , Jastrzębski M.

Geological Quarterly

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2016

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tom Vol. 60, No. 1

106--123

EN

The stability and maintenance of the age record of monazite during post-magmatic processes were studied in granitic and host metasedimentary rocks from the Sudetes (SW Poland). Unaltered monazite in the Kłodzko–Złoty Stok granitoid provided a Th-U-total Pb age of 329 ± 5 Ma, which was related to the late stage of pluton emplacement. In contrast, monazite in the Jawornik granitoid remained unaltered or was partially replaced by secondary phases, including (1) allanite, epidote and, occasionally, apatite; (2) cheralite, allanite and a mixture of clays, Fe oxides and possible unknown rare earth element (REE) phases; and (3) K-feldspar and cheralite with subsequent formation of titanite. Different alteration products on the thin section scale indicate the local character of the post-magmatic processes affecting monazite induced by alkali-rich fluids. The altered and unaltered monazite grains both yielded a Th-U-total Pb age of 343 ± 4 Ma. The Th-U-total Pb ages of the monazite in the accompanying metasedimentary rocks thermally affected by intruding magmas were also constrained. In the paragneiss in contact with the Jawornik granitoid, the unaltered monazite and monazite partially replaced by allanite yielded an age of 344 ± 5 Ma. The monazite from the mica schist, farther from the contact with the granitoids, exhibited an age of 336 ± 4.5 Ma. The 344–336 Ma ages exhibited a record of monazite (re)growth during prolonged Variscan metamorphism. The predominant early Viséan ages constrain the timing of the development of the Złoty Stok Skrzynka Shear Zone and the emplacement of the Jawornik granitoid intrusion. The age results, which are consistent with previous geochronology, indicate that the partial alteration of the monazite did not affect the internal domains or the maintenance of the monazite ages. Thus, this study reveals that monazite geochronology can provide meaningful data in crystalline rocks affected by fluid-induced post-magmatic processes.

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Stability relationships of REE-bearing phosphates in an alkali-rich system (nepheline syenite from the Mariupol Massif, SE Ukraine)

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Dumańska-Słowik M. , Budzyń B. , Heflik W. , Sikorska M.

Acta Geologica Polonica

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2012

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tom Vol. 62, no. 2

247-265

EN

Primary REE-enriched fluorapatite and fluorbritholite-(Ce) in nepheline syenite from the Mariupol Massif (SE Ukraine), contain textural and chemical evidence of late- to post-magmatic metasomatic alteration. REE mobilization and replacement of the primary phases by fluid-mediated coupled dissolution-reprecipitation strongly depended on the distance between the altered minerals in the host rock. Fluorapatite and fluorbritholite-(Ce) forming individual pristine grains were partially replaced by the same phase with a new composition, resulting in the presence of patchy zoning in altered grains. the increased REE contents in altered fluorapatite rim domains are related to REE mobilization from the altered REE-depleted rim domains of the fluorbritholite-(Ce). The REEs were transported by a fluid with high F activity. The alteration of fluorapatite and fluorbritholite-(Ce) grains in contact resulted in the partial replacement of the primary phases by the same phase with a new composition, but also in the partial replacement of the fluorapatite by secondary monazite and fluorite. The REE mobilized from the fluorbritholite-(Ce) in the presence of a F-rich fluid in an alkali-rich system promoted formation of monazite as the new phosphate REE-host. The presence of secondary parisite in the altered domains of the fluorapatite and fluorbritholite-(Ce) indicates a CO2 component in the fluid during metasomatic alteration.

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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)

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Budzyń B. , Jastrzębski M. , Kozub-Budzyń G. A. , Konečný P.

Geological Quarterly

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2015

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tom Vol. 59, No. 4

700--717

EN

Thermodynamic modelling and monazite Th-U-total Pb dating via electron microprobe were used to improve the pressure, temperature and timing constraints of the HP-HT metamorphic record in granulites from Stary Gierałtów (NE Orlica-Śnieżnik Dome (OSD), SW Poland). The thermodynamic calculations constrained the P-T conditions to 20-22 kbar and ca. 920ºC in the felsic to intermediate granulites and 20-22 kbar and ca. 970ºC in the mafic granulite. These conditions are considered to closely represent the peak temperatures experienced by these rocks. In the intermediate granulite, the matrix monazite and monazite inclusions in garnet and allanite yielded an age of 349±2.5 Ma. An HP-HT metamorphic event with temperature conditions exceeding 900ºC, which are greater than the closure temperatures of most geochronometers, must have disturbed and completely reset the isotopic systems, including the Th-U-Pb system in the monazite. Consequently, this resetting prevented us from constraining the age of potential earlier metamorphic events or the igneous protolith. The 349±2.5 Ma age reflects the timing of the late-stage HP-HT event and cooling below 900ºC related to the initial exhumation of the granulites. A comparison of the new P-T-t constraints with previous data from the NE Orlica-Śnieżnik Dome indicates that the activation of the channels that exhumed the HP rocks to mid-crustal depths most likely initiated at ca. 350 Ma, and all the metamorphic rocks in the OSD likely shared a common Variscan evolution after ca. 340 Ma.

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Stability of monazite and disturbance of the Th-U-Pb system under experimental conditions of 250–350 °C and 200–400 MPa

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Budzyń B. , Konečný P. , Kozub-Budzyń G. A.

Annales Societatis Geologorum Poloniae

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2015

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tom Vol. 85, No. 2

405--425

EN

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 starting materials included the Burnet monazite + K-feldspar ± albite ± labradorite + muscovite + biotite + SiO2 + CaF2 and 2M Ca(OH)2 or Na2Si2O5 + 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 resulted from fluid-mediated coupled dissolution-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.

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Late Cambrian protolith age of the Młynowiec-Stronie Group and the Devono-Carboniferous polyphase metamorphic evolution of the Orlica-Śnieżnik Dome (NE Bohemian Massif)

80%

Jastrzębski M. , Budzyń B. , Stawikowski W.

Geologia Sudetica

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2014

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tom Vol. 42

33--34

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Th-U-total Pb timing constraints on the emplacement of the granitoid pluton of Stolpen, Germany

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Lisowiec K. , Budzyń B. , Słaby E. , Schulz B. , Renno A. D.

Acta Geologica Polonica

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2014

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tom Vol. 64, no. 4

457--472

EN

Monazite from the Stolpen monzogranite (SE Germany) was studied to constrain the Th-U-total Pb age of pluton formation. Monazite grains demonstrate subtle to distinct patchy zoning related to slight compositional variations. Textural and compositional characteristics indicate that the monazite formed in a single magmatic event in a slightly heterogeneous system, and was only weakly affected by secondary alteration, which did not disturb the Th-U-Pb system. Chemical dating of the monazite gave a consistent age of 299 ± 1.7 Ma. The current study presents the first geochronological data for the Stolpen granite. It provides evidence that Stolpen is the youngest Variscan granitic intrusion in the Lusatian Granodiorite Complex and indicates that magmatic activity related to post-collisional extension in this region lasted at least 5my longer than previously assumed.

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SHRIMP U-Pb zircon chronology of the Polish Western Outer Carpathians source areas

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Budzyń B. , Dunkley D. J. , Kusiak M. A. , Poprawa P. , Malata T. , Skiba M. , Paszkowski M.

Annales Societatis Geologorum Poloniae

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2011

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tom Vol. 81, No 2

161-171

EN

The Western Outer Carpathians flysch of Poland comprises clasts of crystalline rocks representing source areas that supplied sedimentary basins with clastic material. Zircon from quartz syenite and granite cobbles representing the Silesian Ridge, the currently unexposed source area located at the southern margin of the Silesian Basin, yielded uniform U-Pb dates of 604š6 Ma and 599š6 Ma. These are interpreted as the age of igneous crystallization. Similarly, zircon from a gneiss cobble derived from the northern source terrain gave 610š6 Ma date, which is interpreted as the age of crystallization of the granitic protolith to the gneiss. The Neoproterozoic magmatism is interpreted to have occurred at the Gondwana active margin.

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The CETeG 2014 excursion to crystalline basement of the Orlica–Śnieżnik Dome, the Sudetes

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Żelaźniewicz A. , Budzyń B. , Ilnicki S. , Jastrzębski M. , Murtezi M. , Redlińska-Marczyńska A. , Stawikowski W. , Szczepański J.

Geologia Sudetica

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2014

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tom Vol. 42

125--136