Petrography descriptions and U-Pb zircon datasets from the Archean Pavas Block, Uruguay's Precambrian
Description
Petrography and U-Pb zircon analyses of the granitic – gneisses and migmatites of the Pavas Block, a segment composed of pre-Neoproterozoic basement rocks located westward of the Neoproterozoic Dom Feliciano Belt.
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U-Pb isotopic data and zircon dating was produced at the Geochronological Laboratory of the Geosciences Institute from the University of São Paulo (Brazil). The LA-ICP-MS equipment locates at the CPGeo-IGc/USP and has an excimer laser of ArF gas (193 nm) coupled to the Neptune™ High-Resolution Multi-collector ICP-MS. The excimer laser used here provides a better regularity of abrasion, reducing the fractionation between masses due to its high optical quality and source stability (Sato et al., 2009). The ICP-MS analytical procedure was calibrated using the international standard zircon Temora-1 standard zircon (206Pb/238U = 0.06683). Results are displayed in 206Pb/238U vs. 207Pb/235U Wetherill’s Concordia diagram and 206Pb/238U vs. 207Pb/206Pb Tera-Wasserburg’s graph, using IsoplotR (Vermeersch, 2018). Wetherill’s Concordia diagrams served both to model magmatic protoliths’ concordant age and the systematic radiogenic lead loss due to subsequent geological processes. The zircons were ablated during 40 seconds in the 193 nm Excimer Laser Ablation System, at 7-6 Hz, 6mJ and full energy, obtaining spots of ca. 25 μm (Helium: MFC1 = 0.300 L/min, MFC2 = 0.300 L/min, Argon: Aux.= 0.95 L/min, sample = 0.978 L/min). Zircon's study on binocular microscope and SEM by cathodoluminescence was essential in this research to describe and document internal textures and relate them with the analytical data.