LA-ICP-MS and SIMS U-Pb and U-Th zircon geochronological data of Late Pleistocene lava domes of the Ciomadul Volcanic Dome Complex (Eastern Carpathians)

This article provides laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and secondary ionization mass spectrometry (SIMS) U-Pb and U-Th zircon dates for crystals separated from Late Pleistocene dacitic lava dome rocks of the Ciomadul Volcanic Dome Complex (Eastern Carpathians, Romania). The analyses were performed on unpolished zircon prism faces (termed rim analyses) and on crystal interiors exposed through mechanical grinding an polishing (interior analyses). 206Pb/238U ages are corrected for Th-disequilibrium based on published and calculated distribution coefficients for U and Th using average whole-rock and individually analyzed zircon compositions. The data presented in this article were used for the Th-disequilibrium correction of (U-Th)/He zircon geochronology data in the research article entitled “The onset of the volcanism in the Ciomadul Volcanic Dome Complex (Eastern Carpathians): eruption chronology and magma type variation” (Molnár et al., 2018) [1].

& 2018 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Subject area
Earth Sciences More specific subject area Geochronology, Geochemistry Type of data Tables  How data was acquired Laser-ablation inductively coupled mass spectrometry (LA-ICP-MS); Thermo Element XR Sector Field (SF)-ICP-MS with Resonetics Resolution 155 laser ablation system (ETH Zürich, Switzerland) and Secondary ion mass spectrometry (SIMS; Heidelberg, Germany) Data format LA-ICP-MS: U-Th-Pb isotopic data in.xlsx format corrected for relative sensitivity, drift, alpha-dose and Th-disequilibrium SIMS: U-Th-Pb data in.xlsx format relative sensitivity-corrected and Th-disequilibrium-corrected

Experimental factors
Zircon grains were extracted from bulk lava rocks Experimental features Separated zircon grains were mounted in epoxy resin, polished and mapped by cathodoluminescence technique.

Data source location
Ciomadul Volcanic Dome Complex (Eastern Carpathians) as reported in Table 1.

Data accessibility
Supplementary materials

Value of the data
These data provide high-spatial resolution U-Pb and U-Th zircon ages for the Late Pleistocene Ciomadul Volcanic Dome Complex (Eastern Carpathians); these ages date zircon crystallization and define a maximum age of the eruption.
The difference between zircon crystallization and eruption ages represents the zircon residence time, which infer the time of magma residence underneath Ciomadul Volcanic Dome Complex.
The dataset can be used to refine Th-disequilibrium corrections for (U-Th)/He zircon geochronology [1].
Data enable recognition of redeposition, erosion, and sedimentary transport of volcanic rocks and components from the Ciomadul Volcanic Dome Complex.
These ages are valuable for detrital zircon geochronology in the basins of the Eastern Carpathians, and can identify sediment provenance.

Data
In this article, we report in-situ U-Th and U-Pb zircon geochronological data from dacitic lava of the Ciomadul Volcanic Dome Complex (Eastern Carpathians). Data were generated using different sample preparation strategies and analytical methods: LA-ICP-MS and SIMS analyses were carried out on sectioned and polished crystal interiors, as well as on unpolished crystal surfaces (rims). LA-ICP-MS U-Pb results of more than 500 spot analyses are listed from 8 crystal populations (sample) along Table 1 Details of sample localities and analyses types.

Sample code
Location GPS coordinates Lithology Analyses type Th half-life [13], all other half-lives [14] with 5 zircon reference materials (e.g. GJ-1, Plešovice, 91500, AUSZ7-1, AUSZ7-5 [2][3][4][5][6][7]) performed in three sessions. 46 U-Th and 50 U-Pb SIMS results are reported, representing 4 samples (secondary references were AS3 [8] for U-Th and 91500 for U-Pb). The dataset contains the LA-ICP-MS raw and processed data and the SIMS processed data. Validation reference materials were used to correct for alpha dose-dependent age offsets [18]. Correction was accomplished by modelling the dependence of age offset on total radiation dose, calculated from sample age and concentrations of U and Th [19] in each session. Th disequilibrium correction was performed after alpha dose-correction using the algorithm of [20], assuming a constant Th/U partition coefficient ratio of 0.33 7 0.063 (1σ) [12].

Sample collection
Localities with GPS coordinates and lithology of the samples are shown in Table 1.

Sample preparation
Zircon crystals were separated from the 63-125 µm size fraction of rock samples by standard gravity and magnetic separation methods.
For LA-ICP-MS analyses the separated zircon grains, except for the crystals of CSO-BAL03, were mounted in 1 in. epoxy resin mount and polished to a 1 µm finish. Before dating, zircons were checked by optical microscopic and cathodoluminescence (CL) imaging. CL imaging was produced using an AMRAY 1830 SEM equipped with GATAN MiniCL and 3 nA, 10 kV setup at the Department of Petrology and Geochemistry, Eötvös University, Hungary. Crystals of sample CSO-BAL03 were mounted in 1 in. epoxy resin mount and measured without polishing. For SIMS measurements zircon grains were mounted in epoxy and in indium, details of these preparatory works are presented in Table 2.

LA-ICP-MS and SIMS analyses
LA.ICP-MS analyses were performed at the Department of Earth Sciences, ETH Zürich, Switzerland, and the SIMS analyses at the HIP Lab of the Institute of Geosciences, Heidelberg University, Germany. Analytical setups are presented in Tables 2 and 3.