DOI: 10.5285/612ab314-0398-42a2-8f33-65308a4157dc
title: Geochemical and geochronological data from the Falkland Islands, 2023-2024

description: Geological fieldwork was carried out in the Falkland Islands in March 2022 to help understand the depositional history and provenance of Late Permian sedimentary rocks of East Falkland. To accurately determine their depositional age and precise provenance we conducted a detailed analysis of zircon geochronology and geochemistry. The files provided here include full analytical details and datasets from the laboratories used for the acquisition of U-Pb zircon geochronology and Lu-Hf isotope geochemistry. The data were collected in the interval November 2023 to July 2024 across a number of laboratories: University College London and Australian National University (U-Pb zircon geochronology); British Geological Survey (Lu-Hf isotopes). The analyses were conducted by Ian Millar (Canberra, British Geological Survey) and Andrew Carter (University College London). The analyses were conducted to examine the provenance and depositional history of the sedimentary successions of the Falkland Islands.
description: Analytical methods:
Zircon U-Pb geochronology was conducted at five separate laboratories: 
University College London
Zircon U-Pb geochronology used laser ablation inductively coupled mass spectrometry (LA-ICP-MS) facilities (Agilent 7700 coupled to a New Wave Research 193 nm excimer laser) at the London Geochronology Centre based in University College London. Heavy minerals were separated from bulk sediment samples using standard density liquid and magnetic separation procedures. Zircon-enriched extracts were mounted in hard epoxy resin on glass slides and polished for analysis. Typical laser spot sizes of 25 micrometers were used with a 7-10 Hz repetition rate and a fluence of 2.5 J/cm2. Background measurement before ablation lasted 15 seconds and laser ablation dwell time was 25 seconds. The external zircon standard was Plesovice, which has a TIMS reference age 337.13 +/- 0.37 Ma (Slama et al., 2008). Standard errors on isotope ratios and ages include the standard deviation of 206Pb/238U ages of the Plesovice standard zircon. Time-resolved signals that record isotopic ratios with depth in each crystal were processed using GLITTER 4.5, data reduction software, developed by the ARC National Key Centre for Geochemical Evolution and Metallogeny of Continents (GEMOC) at Macquarie University and CSIRO Exploration and Mining. Processing enabled filtering to remove spurious signals owing to overgrowth boundaries, weathering, inclusions, or fractures. 
Australia National University
Detrital zircon ages were determined using a Sensitive High Resolution Ion Microprobe (SHRIMP) at the Australian National University. Zircons were mounted in epoxy resin, polished to expose the centers of the grains, and gold-coated. Internal zoning and grain characteristics were mapped by microphotography and cathodoluminescence imaging. Clean areas, free of cracks, inclusions and radiation damage were analyzed. Analysis was carried out with a primary O2- beam; secondary ion beam intensities were measured using an ion-counting detector. Calibration was carried out using zircon standards mounted together with the samples (mostly AS-3; Paces & Miller, 1993). Data were reduced for background, mass bias, calibration and common-Pb corrections using Isoplot (Ludwig, 2012). All errors on ages are at the 2sigma level.
Lu-Hf isotope analysis
Isotope analyses were carried out at NIGL using a Thermo Scientific Neptune Plus MC-ICP-MS coupled to a New Wave Research UP193UC Excimer laser ablation system. Helium was used as the carrier gas through the ablation cell with Ar make-up gas being connected via a T-piece and sourced from a Cetac Aridus II desolvating nebulizer. 0.01 l/min of nitrogen were introduced via the nebulizer in addition to Ar in order to minimize oxide formation. Lutetium (175Lu), Ytterbium (172Yb, 173Yb), and Hafnium (176Hf, 178Hf, 179Hf and 180Hf) isotopes were measured simultaneously during static 30 second ablation analyses. The spot size used was 25 µm; fluence = 8 J/cm2. 
Hf reference solution JMC475 was analyzed during the analytical session and sample 176Hf/177Hf ratios are reported relative to a value of 0.282160 for this standard. Correction for 176Yb on the 176Hf peak was made using reverse-mass-bias correction of the 176Yb/173Yb ratio empirically derived using Hf mass bias corrected Yb-doped JMC475 solutions (Nowell & Parrish, 2001). 176Lu interference on the 176Hf peak was corrected by using the measured 175Lu and assuming 176Lu/175Lu = 0.02653.
Hf-isotope data was processed using the Iolite data reduction package (Paton et al., 2011). 
Three zircon reference materials (91500, Mud Tank, GJ1) were analyzed throughout the analytical session. The 91500 zircon reference material was used as the primary standard in Iolite, and was used to normalize the 176Lu/177Hf ratio assuming a value of 0.000311 (Woodhead & Hergt, 2005).
description: U-Pb ages were calculated using the 206Pb/238U ratios for samples dated as &lt;1.1 Ga, and the 207Pb/206Pb ratios was used for older grains. Discordance was determined using (207Pb/235U - 206Pb/238U) / 206Pb/238U) and similar for 207Pb/206Pb ages. 
Lu_Hf analytical uncertainties for unknowns were propagated by quadratic addition to include the standard error of the mean of the analysis and the reproducibility of the 91500 reference material. εHf values were calculated using a 176Lu decay constant of 1.867 x 10-11y-1 (Söderlund et al., 2004), the present-day chondritic 176Lu/177Hf value of 0.0336 and 176Hf/177Hf ratio of 0.282785 (Bouvier et al., 2008).