Data of thermal imprints of late Permian Emeishan basalt effusion: Evidence from zircon fission-track thermochronology

We present 271 detrital single-grain zircon fission track (ZFT) ages obtained for eight sandstones, which were sampled from the southwestern Yangtze Craton, southern China. Accessory minerals were concentrated using standard crushing, sieving, electro-magnetic and heavy liquid mineral separation techniques. Zircon grains were mounted on FEP Teflon and polished to expose their internal surfaces to 4π geometry. Two to three mounts of each sample were etched in KON:NaOH eutectic melt at ∼228 °C for 12–60 hours to reveal spontaneous fission tracks. Etched mounts were covered with a uranium-free muscovite external detector for the irradiation with thermal neutrons. CN2 standard uranium glasses were embedded with the age standards (Fish Canyon Tuff zircons). After irradiation, external mica detectors were removed from sample mounts and then etched in 48% HF at room temperature for 30 min to reveal induced tracks. Fission track counting was performed using a Zeiss Axiotron microscope at a total magnification of 1250 × . Zircon fission-track ages were calculated using the ζ-calibration technique. The central ages (with 1σ error) vary from 144.7 ± 4.9 Ma to 256.7 ± 9.6 Ma, with variable P(χ2) values of 0%–75%. ZFT ages of the five Cambrian to Ordovician samples are younger than their depositional ages, and thus were fully reset by post-depositional heating. ZFT ages of three Jurassic samples are partially reset, as they overlap with or slightly younger than the corresponding depositional ages.