Mineralogy and geochemistry of the Făgăraș marbles (Southern Carpathians, Romania)

Published: 27 March 2026| Version 1 | DOI: 10.17632/f9cdtgfbd8.1
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Description

The dataset comprises analytical results of EPMA performed on marbles from amphibolite facies (retrogressed to greenschist and sub-greenschist facies) in the Făgăraș Mountains, central Southern Carpathians. The marbles are components of an intriguing metamorphic unit (Făgăraș terrane) originated from the northern Gondwana margin that accreted to the roots of the Carpathian orogen during its pre-Alpine evolution. We used EPMA data combined with optical mineralogy (microscopic examination of thin sections) to achieve more consistent information on mineral assemblages in the metasedimentary carbonates of the Făgăraș terrane. These would further provide insights on the long and complicated geologic history not only of the marbles, but of the entire rock pile they are comprised within, from protolith to (poly)metamorphic and late hydrothermal activity. Most marbles are dolomitic, inherited from the sedimentary protolith, but also calcitic marbles are present, with calcite replacing dolomite during metamorphism. Samples were collected from marble bands outcropping in the upper Bâlea Valley, at Bâlea Lake, Capra Lake, Fundu Caprei glacial valley, Bâlea Tunnel, Peak 2000, Museteica Mt, and Lespezi Mt. The first version of this dataset contains two tables with the results of ion microprobe analytical data performed on carbonate, silicate and other minerals that form the marble bands in the central Făgăraș unit. In addition, BSE images and EDS analysis on carbonates and mineral micro-inclusions provide visual and analytical details regarding the geochemical composition of the Făgăraș marbles. The dataset stands as supplementary material for an ongoing study on the mineralogy, geochemistry and thermobarometry of the Făgăraș marble, a pilot approach that would allow in-depth knowledge on the geologic evolution of a little known (yet) Carpathian terrane.

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EPMA data acquisition was carried out at Rice University, Department of Earth, Environment and Planetary Science, using a Jeol JXA 8530F Hyperprobe, with a field emission assisted thermo-ionic (Schottky) emitter, equipped with five Wavelength Dispersive Spectrometers (WDS). Analytical conditions employed for the quantitative analysis were: 15 kV acceleration voltage, 10 nA beam current, defocused 1-5-micron beam size (depending on the size of the carbonate grain). The PRZ (JEOL) matrix correction was employed for quantification. Standards used for quantification were natural minerals, as follows: olivine (Fo93), dolomite, rhodonite, celestine and barite. Carbon wt% was estimated by difference. Some microprobe session used plagioclase for Ca and olivine for Mg. Every microprobe session started with calibrations and analyzing secondary standards. The reproducibility of secondary standards (carbonates and silicates) was achieved with errors below 2%. The data reduction was done by calculating the cation numbers normalized to 6 oxygen atoms. Silicon was analyzed in the same time with the other elements in order to evaluate the mixed effect of carbonate and quartz or other silicates in the analytical volume. The analytical conditions employed for silicate analysis were: 15 kV acceleration voltage, 20 nA beam current, ca. 50 nm beam size, except for feldspars, where a larger beam (20 microns) was used, in order to avoid loss of Na and K. The standards used for calibration were natural minerals: olivine (Fo93), plagioclase, rhodonite, rutile, chromite, pentlandite, jadeite, and biotite. The PRZ matrix correction method was used for quantification. The fast identification of mineral phases in all samples was done by Energy Dispersive Spectrometry (EDS) analysis at Rice University, Department of Earth, Environmental and Planetary Sciences, using a JEOL Silicon Drift (SD) X-ray Detector with 10mm² active area and 133eV resolution (attached to the JEOL JXA 8530F Hyperprobe). The analytical conditions used for EDS analysis were: 15 kV accelerating voltage, 20 nA beam current, live time 20 seconds. DeadTime (DT) during the analysis was 35-40% with count rates ranging from ~45,000 to ~100,000. The beam size used was “spot” size (~300 nm), due to the small size of the analyzed particles.

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Metamorphic Geochemistry, Metamorphic Petrology, Rare Earth Element, Zircon

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