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Vozar J.,Slovak Academy of Sciences | Spisiak J.,Matej Bel University | Vozarova A.,Comenius University | Bazarnik J.,Polish Geological Institute National Research Institute | Krai J.,DionYz Stur State Geological Institute
Geologica Carpathica | Year: 2015

The paper presents new major and trace element and first Sr-Nd isotope data from selected lavas among the Permian basaltic andesite and basalts of the Hronicum Unit and the dolerite dykes cutting mainly the Pennsylvanian strata. The basic rocks are characterized by small to moderate mg# numbers (30 to 54) and high SiO2 contents (51-57 wt. %). Low values of TiO2 (1.07-1.76 wt. %) span the low-Ti basalts. Ti/Y ratios in the dolerite dykes as well as the basaltic andesite and basalt of the 1st eruption phase are close to the recommended boundary 500 between high-Ti and low-Ti basalts. Ti/Y value from the 2nd eruption phase basalt is higher and inclined to the high-Ti basalts. In spite of this fact, in all studied Hronicum basic rocks Fe2O3∗ is lower than 12 wt. % and Nb/La ratios (0.3-0.6) are low, which is more characteristic of low-Ti basalts. The basic rocks are characterized by Nb/La ratios (0.56 to 0.33), and negative correlations between Nb/La and SiO2, which point to crustal assimilation and fraction crystallization. The intercept for Sr evolution lines of the 1st intrusive phase basalt is closest to the expected extrusions age (about 290 Ma) with an initial 87Sr/86Sr ratio of about 0.7054. Small differences in calculated values ISr document a partial Sr isotopic heterogeneity source (0.70435-0.70566), or possible contamination of the original magma by crustal material. For Nd analyses of the three samples, the calculated values εCHUR (285 Ma) are positive (from 1.75 to 3.97) for all samples with only subtle variation. Chemical and isotopic data permit us to assume that the parental magma for the Hronicum basic rocks was generated from an enriched heterogeneous source in the subcontinental lithospheric mantle. © Geologica Carpathica 2015. Source


Majka J.,Uppsala University | Be'eri-Shlevin Y.,Swedish Museum of Natural History | Gee D.G.,Uppsala University | Ladenberger A.,Uppsala University | And 5 more authors.
Journal of Geosciences | Year: 2012

Monazite from granulite-facies rocks of the Åreskutan Nappe in the Scandinavian Caledonides (Seve Nappe Complex, Sweden) was dated using in-situ U-Th-total Pb chemical geochronology (CHIME). Multi-spot analyses of a non-sheared migmatite neosome yielded an age of 439 ± 3 Ma, whereas a sheared migmatite gave 433 ± 3 Ma (2σ). Although the obtained dates are rather similar, a continuous array of single dates from c. 400 Ma to c. 500 Ma suggests possibly a more complex monazite age pattern in the studied rocks. The grouping and recalculation of the obtained results in respect to Y-Th-U systematics and microtextural context allowed distinguishing several different populations of monazite grains/growth zones. In the migmatite neosome, low-Th and low-Y domains dated at 455 ± 11 Ma are considered to have grown under highgrade sub-solidus conditions, most likely during a progressive burial metamorphic event. The monazites with higher Th and lower Y yielded an age of 439 ± 4 Ma marking the subsequent partial melting event caused by decompression. The youngest (423 ± 13 Ma) Y-enriched monazite reveals features of fluid-assisted growth and is interpreted to date the emplacement of the Åreskutan onto the Lower Seve Nappe. In the sheared migmatite, the high-Th and low-U (high Th/U) monazite with variable Y contents yielded an age of 438 ± 4 Ma, which is interpreted to date the partial melting event. Relatively U-rich rims on some of the monazite grains again reveal features of fluid-assisted growth, and thus their age of 424 ± 6 Ma is interpreted as timing of the nappes emplacement. These results call, however, for further more precise, isotopic (preferably ion microprobe) dating of monazite in the studied rocks. Source


Petrik I.,Slovak Academy of Sciences | Janak M.,Slovak Academy of Sciences | Froitzheim N.,University of Bonn | Georgiev N.,Sofia University | And 4 more authors.
Journal of Metamorphic Geology | Year: 2016

Evidence for ultrahigh-pressure metamorphism (UHPM) in the Rhodope metamorphic complex comes from occurrence of diamond in pelitic gneisses, variably overprinted by granulite facies metamorphism, known from several areas of the Rhodopes. However, tectonic setting and timing of UHPM are not interpreted unanimously. Linking age to a metamorphic stage is a prerequisite for reconstruction of these processes. Here, we use monazite in diamond-bearing gneiss from Chepelare (Bulgaria) to date the diamond-forming UHPM event in the Central Rhodopes. The diamond-bearing gneiss comes from a strongly deformed, lithologically heterogeneous zone (Chepelare Mélange) sandwiched between two migmatized orthogneiss units, known as Arda-I and Arda-II. Diamond, identified by Raman micro-spectroscopy, shows the characteristic band mostly centred between 1332 and 1330 cm-1. The microdiamond occurs as single grains or polyphase diamond + carbonate inclusions, rarely with CO2. Thermodynamic modelling shows that garnet was stable at UHP conditions of 3.5-4.6 GPa and 700-800 °C, in the stability field of diamond, and was re-equilibrated at granulite facies/partial melting conditions of 0.8-1.2 GPa and 750-800 °C. The texture of monazite shows older central parts and extensive younger domains which formed due to metasomatic replacement in solid residue and/or overgrowth in melt domains. The monazite core compositions, with distinctly lower Y, Th and U contents, suggest its formation in equilibrium with garnet. The U-Th-Pb dating of monazite using electron microprobe analysis yielded a c. 200 Ma age for the older cores with low Th, Y, U and high La/Nd ratio, and a c. 160 Ma age for the dominant younger monazite enriched in Th, Y, U and HREE. The older age of c. 200 Ma is interpreted as the timing of UHPM, whereas the younger age of c. 160 Ma as granulite facies/partial melting overprint. Our results suggest that UHPM occurred in Late Triassic to Early Jurassic time, in the framework of collision and subduction of continental crust after the closure of Paleotethys. © 2016 John Wiley & Sons Ltd. Source


Budzyn B.,Polish Academy of Sciences | Budzyn B.,Jagiellonian University | Konecny P.,DionYz Stur State Geological Institute | Kozub-Budzyn G.A.,AGH University of Science and Technology
Annales Societatis Geologorum Poloniae | Year: 2015

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 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 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. © 2015, Geological Society of Poland. All rights reserved. Source


Petrik I.,Slovak Academy of Sciences | Kubis M.,Geofos Ltd. | Konecny P.,DionYz Stur State Geological Institute | Broska I.,Slovak Academy of Sciences | Malachovsky P.,Kerko
Canadian Mineralogist | Year: 2011

A small body of Permian high-P Li-F microgranite accompanied by medium-grained leucogranite occurs in the western Gemeric unit of the Western Carpathians; it occurs amongst other F-B-bearing specialized S-type granite massifs. Besides phenocrystic topaz and zinnwaldite, the microgranite matrix contains a characteristic assemblage of rare aluminophosphates (arrojadite, lacroixite, viitaniemiite), goyazite and gorceixite, along with late apatite. The assemblage is unusual in granitic rocks; it formed as a result of a buildup of P in the residual melt (matrix) during crystallization of mostly quartz and alkali feldspars. Topaz and lacroixite or viitaniemiite were stable instead of albite and apatite. In the absence of biotite, the increasing Fe and Mn stabilized arrojadite. Both types of granite were reworked during the Cretaceous Alpine burial, which probably resulted in the influx of Sr and Ba in low-temperature fluids. Topaz - muscovite and feldspar thermometers indicate that the temperature of fluids was below 300°C, when goyazite, gorceixite and clay overgrew earlier apatite and arrojadite. The phosphate assemblage observed in the microgranite is stable at CaO/P2O5 less than 1 and Li2O/F less than 0.21. At higher values characteristic of other Li-F-P granite occurrences, apatite, amblygonite and lepidolite take the place of aluminophosphates and zinnwaldite. Source

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