New Developments in Incremental Heating Detrital 40Ar/39Ar Lithic (DARL) Geochronology using Icelandic River Sand

• Main Authors: Okwueze, Odinaka, Konrad, Kevin, Capaldi, Tomas
• Format: Text
• Language: English
• Published: 2024
• Subjects: Greenland; Iceland; North Atlantic
• Online Access: https://doi.org/10.5194/egusphere-2024-1299; https://egusphere.copernicus.org/preprints/2024/egusphere-2024-1299/

Iceland records over fifteen million years of complex volcanism resulting from the intersection of mid-ocean ridge and mantle plume upwelling. The Iceland mantle plume has been active for at least 70 Ma, with surface expressions in Greenland, the North Atlantic, and Iceland. The Iceland hotspot may exhibit periods of increased volcanic output linked to pulses of upwelling within the plume. Understanding Iceland’s magmatic history and potential pulsation could provide key insights into dynamic topography driving changes in deep-water oceanic circulation, late Cenozoic climate change and mantle plume – mid-ocean ridge interaction. Detrital geochronology is a powerful tool for capturing the magmatic history of a region. However, Iceland's fine-grained extrusive volcanic lithologies lack the typical detrital mineral phases such as zircon, sanidine, hornblende, and rutile that current geochronology methods utilize. Here we present a new methodology for capturing the magmatic history of fine grained extrusive volcanic rocks using single grain detrital 40 Ar/ 39 Ar incremental heating geochronology. The DARL (or Detrital Argon Lithics) method thus far has consisted of 40 Ar/ 39 Ar total fusion analyses, which pose a problem in the case of Iceland, due to the nature of its young glassy lava flows commonly displaying subatmospheric 40 Ar/ 36 Ar isochron intercepts and low 40 Ar*. This work represents a 40 Ar/ 39 Ar incremental heating pilot study on 19 single grains of Icelandic river sand (1–3 mm), collected from five different catchments. Fifteen of the 19 basaltic grains produced concordant age experiments that ranged from 0.2 to 13.5 Ma and uncertainties (2σ) from 1 % to 86 % with the grains under 1 Ma having the largest uncertainties. Preliminary results show that basaltic grains with less alteration (and corresponding lower atmospheric argon concentration) yield more accurate age determinations, though altered basaltic grains can still produce statistically valid age ...