Gabriela Anna Kozub-Budzyń

The geochronological and geochemical records of zircon bear information to unravel the magmatic and metamorphic origin of rocks and their hydrothermal history. In this context, we investigated zircon from nepheline syenite dykes from the Variscan Čistá pluton (the Teplá-Barrandian Unit of the Bohemian Massif), which are known for hosting complex Zr-REE-Nb-rich mineralization. The study is focused on investigating, using modern geochemical techniques, the effects of alteration processes on zircon stability in an alkali-rich environment and disturbance of the U-Pb geochronological record from the micro- to the nanoscale. The zircon grains display a complex sponge-like microporous texture composed of heterogeneous zoning as the result of dissolution-recrystallization processes. This enabled significant element mobilization and resulted in partial repairs in the metamict domains achieving almost ideal crystalline structures. Preliminary U-Pb dating revealed a broad distribution of apparent ages (374–450 Ma), with the largest population of zircon grains yielding ages from 450 to 403 Ma. These are interpreted to be derived from an older protolith or a partial remnant of previously unrecognized magmatic event, which got overprinted by subsequent fluid-induced alteration during syenite formation in the main magmatic event of the Čistá pluton ca. 375 Ma. Few zircon grains yielded ages of 320 Ma, significantly younger than the rest of population, which most likely represent a new generation formed during post-magmatic processes. Our study highlights how fluid-induced alteration processes extensively affected the geochronological and compositional signatures of zircon from the nepheline syenite, and provided new insights in understanding the fluid-rock evolution in the context of Čistá pluton.

Results of microanalysis study of NWA 869 meteorite, an ordinary chondrite, where silicates, Fe‐Ni alloys, and troilite are major constituents, are reported. The presented study of microtextures in metallic and sulfide grains provides information on processes occurring from the asteroid's accretion, through the impacts until cooling. The presence of metal–silicate emulsion, swiss‐cheese texture, and polycrystalline kamacite–troilite aggregates observed indicates very rapid increase in temperature due to impact. Fizzed troilite, slightly homogenized taenite domains, and intergrowth of native copper in plessite imply rapid cooling in isolated regions in space. Agrell effect on the interface of kamacite–taenite grains and non‐corroded tetrataenite rims indicates that the sample contains rock fragments from a region unaffected directly by the impact or rapid heating. Diversity of petrological types, lithic clasts with shock grade higher than S3, shock‐darkened clasts or impact melting rocks, and variation of microtextures suggest that the parent body of L‐type chondrites after accretion, radiogenic metamorphism, and consequent formation of the onion–shell model broke up into debris after the impact of eucrite body.

This work presents an investigation of naturally and experimentally unaltered and altered monazite-(Ce) and xenotime-(Y), as well as secondary phases and synthetic REE phosphates (YPO4 and LaPO4–LuPO4) with Raman microspectroscopy, using 488 nm, 532 nm, 633 nm and 780 nm excitation lasers, supplemented by electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). Monazite-(Ce) spectra of the 532 nm laser from experimental products display a wide range of band positions of the v1(PO4) symmetric stretching band from 962 to 981 cm-1. Secondary fluorcalciobritholite spectra display a prominent band at 962–965 cm-1, a broader band at ca. 860 cm-1 and broad distinct luminescence effects at mid-range. Xenotime-(Y) spectra from experimental products display only minor spectral changes, except for a few spectra near secondary Y-rich fluorcalciobritholite. Spectra of Y-rich fluorcalciobritholite from 532 nm laser display characteristic broad luminescence effects at the range of 1500–3000 cm-1, including a strong luminescence band at ca. 2600 cm-1 (Sm3+ electronic transition), and are accompanied by a broad band at 974 cm-1 (488 nm laser) and 964 cm-1 (633 nm laser). The characteristic changes in monazite-(Ce) spectra near secondary phases are emphasised with hyperspectral maps and EPMA-WDS X-ray compositional maps, which provide spatial context and reveal underlying interferences, important to be noted, when evaluating altered minerals. In all cases, experimental and natural, high values of the full width at half maximum (FWHM) of the v1(PO4) band of unaltered monazite-(Ce) domains represent moderate radiation damage. In contrast, lower FWHM values were observed in altered domains. This work expands the Raman database onto examples of naturally and experimentally altered monazite-(Ce) and xenotime-(Y) enabling the identification of internal structural changes in unaltered and altered domains and differentiation of monazite-(Ce) or xenotime-(Y) from fluorcalciobritholite, Y-rich fluorcalciobritholite and other secondary phases.

The petrochronological records of eclogites in the Scandinavian Caledonides are investigated using EPMA and LA-ICPMS of zircon and apatite for U–Pb geochronology, combined with major and trace element characteristics. Metamorphic zircon from two eclogites from the Lofoten-Vesterålen Complex (Lofoten Archipelago region) collectively yielded a Concordia age 427.8 ± 5.7 Ma and an upper intercept U–Pb age 425 ± 30 Ma. Apatites from the same eclogites provided U–Pb lower intercepts at 322 ± 28 Ma and 354 ± 33 Ma, with the latter also yielding a younger age of 227 ± 24 Ma. Two eclogites from the Lower Seve Nappe (Northern Jämtland) demonstrate different zircon and apatite age records. Metamorphic zircon provided Concordia ages of 467.2 ± 5.9 Ma and 444.5 ± 5.5 Ma, which resolve the age of prograde metamorphism and zircon growth during retrogression, respectively. The lower intercept U–Pb ages of apatites from the same eclogites are 436 ± 18 and 415 ± 25 Ma, respectively. In combination with their geochemical characteristics, they suggest two separate stages of exhumation of eclogite bodies in the Lower Seve Nappe. Zircons from an eclogite from the Blåhø Nappe (Nordøyane Archipelago) yielded a continuum of concordant U–Pb dates from ca. 435 to 395 Ma, which suggests several cycles of HT metamorphism within short intervals. Distinctive trace element characteristics of apatites from the Blåhø Nappe eclogite suggest formation coeval with zircon and garnet during HT metamorphism, but Pb diffusion behaved as an open system until cooling during exhumation of the nappe at 390 ± 12 Ma (lower intercept U–Pb age of apatite). To summarize, this study presents the high potential of coupled zircon and apatite petrochronology of eclogites in resolving their metamorphic evolution, particularly with respect to using trace element characteristics of apatites to constrain the records of their growth, alterations and the meaning of their U–Pb age record.

Late Pleistocene–Holocene rocks from the western part of Cocos-Nazca Spreading Centre (C-NSC) include ferromanganese crusts that elucidate the geochemistry and mineralogy of a deep-sea geological setting. Six representative Fe-Mn crust samples were studied using petrological methods, such as optical transmitted light microscopy, energy dispersive X-ray fluorescence spectrometry, inductively coupled plasma mass spectrometry, bulk X-ray diffraction, scanning electron microscopy and electron probe microanalysis. Geochemical, mineralogical and petrological signatures indicate complex formation influenced by mild hydrothermal processes. These crusts consist mostly of mixed birnessite, todorokite-buserite, and Mn-(Fe) vernadite with traces of diagenetic manganates (asbolane), Fe-oxides and oxyhydroxides or hydrothermally associated and relatively pure Mn-oxyhydroxides (manganite). The average Mn/Fe ratio is 2.7, which suggests predominant mixed hydrogenous-early diagenetic crusts with hydrothermal influences. The mean concentrations of three prospective metals (Ni, Cu and Co) are low: 0.17, 0.08 and 0.025 wt %, respectively. The total content of ΣREY is also low, and ranges from 81 to 741 mg/kg (mean 339 mg/kg). We interpret the complex geochemical and mineralogical data to reflect mixed origin of the crusts, initially related with formation of hydrothermal plume over the region. This process occurred during further interactions with seawater from which additional diagenetic and hydrogenetic elemental signatures were acquired.

In the Variscides of central Europe, the tectonothermal history of a few units jointly assigned to the Teplá‐Barrandian/Bohemian microplate had already terminated in the Devonian. One of these is the Góry Sowie Massif (GSM; Sudetes, SW Poland), mainly consisting of variably migmatitic gneisses with subordinate granulite and peridotite inserts. The eo‐Variscan evolution of the GSM was completed in five tectonothermal stages; however, the timing and pressure–temperature (P–T) conditions of the individual stages remain unclear because isotopic ages overlap within error, and previousP–Testimates have been determined without reference to these ages. Our thermodynamic modelling and LA–ICP–MS U–Pb and electron probe microanalysis (EPMA) U–Th–total Pb monazite geochronology provide new insights into the early Variscan multistage evolution of the GSM. The newP–T–time (t) data show that granulites were metamorphosed concurrently with gneisses but at different depths and temperatures. During subduction of Saxothuringia beneath Teplá‐Barrandia at 395–390 Ma, the granulites of crustal provenance experienced high‐P–high‐Tconditions (740–750°C, 17–18 kbar) and came in contact with the overlying mantle. Slab break‐off gave rise to decompression from conditions of ~17 kbar/840°C to 11–12 kbar/850–860°C, which continued at 380–370 Ma when the granulites were sheared off and extruded as tectonic slices to lower–middle crustal depths, where gneisses were undergoing metamorphism and migmatization under amphibolite facies conditions. In the gneisses, the oldest monazite date ofc. 390 Ma constrains the age of the early tectonometamorphic event D₁. Two subsequent events (D₂and D₃, sillimanite grade) occurred under conditions of 660–680°C and 5–9 kbar at 380–375 Ma, when, in various parts of the future massif, the gneisses were (re)folded and migmatized due to heat arising from underplated mantle. Isostatic exhumation was accompanied by pegmatite intrusions (D₄) at 370 Ma and subsequent orogenic collapse (D₅). Concurrently, high temperature conditions (~700°C) promoted a disturbance of the U–Pb system in monazite in some granulites.

Titanite from various rocks of the Karkonosze granitoid pluton (South-Eastern Poland) was studied, in order to evaluate its precision in recording magma evolution processes. The rocks are of lamprophyric, dioritic, granodioritic and granitic composition, including hybrid structures such as microgranular magmatic enclaves and composite dykes. Based on textures, chemistry and Zr-in-titanite geothermometry, titanites can be divided into magmatic and post-magmatic populations. Late- to post-magmatic titanite is present in almost all rock types, especially in the most evolved ones (where magmatic titanite is absent) and can be characterized by low trace element and high Al and F contents. Magmatic titanite crystallized in temperatures between 610 and 870 °C, after apatite and relatively simultaneously with amphibole and zircon. Titanite from lamprophyre exhibits compositional features typical of titanites formed in mafic rocks: low Al and F, high Ti⁴⁺/(Al + Fe³⁺), LREE (light rare earth elemet)-enriched chondrite-normalized REE patterns, low Y/Zr, Nb/Zr, Lu/Hf, high (Ce + Nd)/Y, Th/U and Zr. Titanite from hybrid rocks inherited these characteristics, indicating major contribution of the mantle-derived magma especially during early stages of magmatic evolution. Titanite compositional variations, as well as a wide range of crystallization temperatures in hybrid granodiorites point to prolonged crystallization from distinct magma domains of variable mafic versus felsic melt proportions. The extent of compositional variations decreases through subsequent stages of magmatic evolution, and titanite with the least contribution of the mafic component is characterized by higher total REE, Al and F contents, lower Ti⁴⁺/(Al + Fe³⁺), (Ce + Nd)/Y and Th/U ratios, LREE-depleted chondrite-normalized REE patterns and higher Y/Zr, Nb/Zr and Lu/Hf ratios. Titanite composition from the intermediate and late stage hybrids bears signature of decreasing amount of the mafic melt and higher degree of its evolution, however, the exact distinction between the former and the latter is very limited.

Allanite is one of the main rare earth elements (REE)-rich accessory minerals in composite dykes from the granitoid pluton of Karkonosze. These dykes differ in composition from the bulk of the pluton by elevated rare earth elements (REE), Y, Zr, and alkali contents, suggesting contribution of an additional component. Allanite exhibits complex alteration textures, which can be divided into two stages. The first stage is represented by allanite mantles, formed by fluid infiltration into previously crystallized magmatic allanite. These zones have low totals, are Ca-, Al-, Mg-, and light REE (LREE)-depleted, and Y-, heavy REE (HREE)-, Th-, Ti-, and alkali-enriched. The fractionation between LREE and HREE was caused by different mobility of complexes formed by these elements in aqueous fluids. The second stage includes recrystallized LREE-poor, Y-HREE-rich allanite with variable Ca, Al, Mg, and REE-fluorocarbonates. The alteration products from both stages demonstrate higher Fe³⁺/(Fe²⁺ + Fe³⁺) ratios and a negative Ce anomaly. These features point to the alkaline, low-temperature, and oxidized nature of the fluids. The differences in mobility and solubility of respective ligands show that the fluids from the first stage may have been dominated by Cl, whereas those of the second stage may have been dominated by F and CO₂ (and PO₄ in case of one sample). The inferred chemistry of the fluids resembles the overall geochemical signature of the composite dykes, indicating a major contribution of the hydrothermal processes to their geochemical evolution.

Indium in polymetallic mineralisation at the Gierczyn mine, Karkonosze-Izera Massif, Poland: results of EPMA and LA-ICP-MS investigations

Time constraints on experimental studies of lead apatites