Detrital zircon U-Pb LA-MC-ICP-MS data, Villa Mónica, Cerro Largo and Olavarría formations (Tandilia System, Argentina)
Description
This dataset contains in situ U-Pb isotopic data for detrital zircons from three Neoproterozoic sedimentary units of the Tandilia System (Río de la Plata Craton, Buenos Aires Province, Argentina): the basal Villa Mónica Formation (sample VMF-01), the lower member of the Cerro Largo Formation (sample CL-INF) and the lower Olavarría Formation (sample OF-03), Olavarría area. The data support the manuscript "Provenance shift in the oldest sedimentary cover of the Río de la Plata Craton (Tandilia System, Argentina): new constraints from detrital zircon U-Pb geochronology" (Gómez-Peral et al., submitted to Journal of South American Earth Sciences). Analyses were performed by LA-MC-ICP-MS at the Centro de Pesquisas Geocronológicas (CPGeo), Universidade de São Paulo, Brazil. The system was a Thermo Scientific Neptune coupled to an Analyte Excite 193 nm excimer laser (20 µm spot, 6 Hz, 0.89 J/cm²). GJ-1 was used as the primary reference material and Plešovice as the secondary reference material; the results for both are included. Common Pb was corrected using the Stacey and Kramers (1975) model. The file contains one sheet per sample (Tables S1–S3), with isotopic ratios, Pb, Th and U concentrations, Th/U, apparent ages, concordance, the best age adopted, and whether each analysis was used or rejected. The best age is the ²⁰⁶Pb/²³⁸U age for analyses younger than 1300 Ma and the ²⁰⁷Pb/²⁰⁶Pb age for older ones. Analyses with concordance outside 90–110% (²⁰⁶Pb/²³⁸U vs ²⁰⁷Pb/²³⁵U ages), common Pb above 10% or 1σ uncertainties above 15% were rejected. A total of 279 analyses were accepted: 91 from VMF-01, 99 from CL-INF and 89 from OF-03. All uncertainties in the tables are 1σ.
Files
Steps to reproduce
Sampling: three samples were collected from outcrops and borehole cores in the Olavarría area (Tandilia System, Buenos Aires Province, Argentina): VMF-01 (basal Villa Mónica Formation), CL-INF (lower member of the Cerro Largo Formation) and OF-03 (lower Olavarría Formation). Zircon separation: samples were crushed and jaw-milled, and heavy minerals were concentrated with a Wilfley table and magnetic separation. Zircon grains were hand-picked at random, mounted in epoxy resin and polished to expose their interiors. Imaging: mounts were imaged by cathodoluminescence (SEM, CPGeo, 15 kV) to document internal textures and select spot locations. U-Pb analysis: LA-MC-ICP-MS at the Centro de Pesquisas Geocronológicas (CPGeo), Universidade de São Paulo, with a Thermo Scientific Neptune MC-ICP-MS coupled to an Analyte Excite 193 nm excimer laser (6 Hz, 4.5 mJ, 0.89 J/cm², 20 µm spot, He carrier gas). Each analysis consisted of 40 integrations of ~1 s: 10 for the blank and 30 during ablation. 206Pb, 208Pb, 232Th and 238U were measured in Faraday cups, and 202Hg, 204Pb and 207Pb in ion counters. 235U was calculated from 238U (238U/235U = 137.88), and the 204Hg interference was corrected using 202Hg/204Hg = 4.355. Data reduction: the blank was subtracted and common Pb was corrected with the Stacey and Kramers (1975) model. GJ-1 (608.5 ± 0.4 Ma) was the primary reference material, analysed approximately every 10 minutes to correct for drift and mass fractionation and to calibrate Pb, Th and U concentrations. Plešovice (337.13 ± 0.37 Ma) was analysed as a secondary reference material to monitor accuracy; results are in the sheet "Reference materials". Data selection: the best age is the 206Pb/238U age for analyses with 207Pb/206Pb ages younger than 1300 Ma, and the 207Pb/206Pb age for older analyses. Analyses were rejected when concordance (206Pb/238U vs 207Pb/235U ages) was outside 90–110%, common Pb exceeded 10%, or the 1σ uncertainty of the best age exceeded 15%. The "Status" and "Rejection reason" columns identify each case. All uncertainties are 1σ. Data visualization: age probability density plots and maximum depositional age calculations were produced with IsoplotR (Vermeesch, 2018) using the analyses marked "Used".
Categories
Funders
- Universidade de São PauloSão Paulo, São PauloGrant ID: Centro de Pesquisas Geocronológicas (CPGeo), Universidade de São Paulo (laboratory of M.A.S. Basei)