Laser (U‐Th)/He thermochronology of detrital zircons as a tool for studying surface processes in modern catchments

Abstract

[1] Detrital mineral thermochronology of modern sediments is a valuable tool for interrogating landscape evolution. Detrital zircon (U-Th)/He thermochronology is of particular interest because zircons are durable and withstand transport in glacial and fluvial systems far better than, for example, apatite. However, because of the time-intensive nature of conventional zircon (U-Th)/He thermochronology, most previous studies of this kind have relied on data for a few tens of grains, even though conventional wisdom holds that a substantially larger number is necessary for a robust characterization of the population of cooling ages in a sample. Here, we introduce a microanalytical approach to detrital zircon (U-Th)/He thermochronology that addresses many factors that can complicate the interpretation of conventional zircon (U-Th)/He data, particularly with respect to alpha ejection and injection and U + Th zoning. In addition, this technique permits the effective dating of naturally abraded and broken grains, and, therefore, lessens the potential for sampling bias. We apply both conventional and laser microprobe techniques to a detrital sample from the Ladakh Range in the northwestern Indian Himalaya, showing that the two yield very similar principal modes of apparent ages. However, the laser microprobe data yield a broader spectrum of ages than that of the conventional data set, which we interpret to be caused by bias related to the selection requirements for zircons used for conventional dating. This method thus provides a time-efficient route to obtaining a higher-resolution distribution of dates from a single sample, which will, in turn, yield higher-fidelity constraints regarding catchment-wide erosion rates for surface process studies.Citation: Tripathy-Lang, A., K. V. Hodges, B. D. Monteleone, and M. C. van Soest (2013), Laser (U-Th)/He thermochronology of detrital zircons as a tool for studying surface processes in modern catchments,

Identifying spatial variations in glacial catchment erosion with detrital thermochronology

“…Recent work by Tripathy‐Lang et al . [] using zircon (U‐Th)/He laser ablation analyses presents a promising new tool to avoid any bias in grain selection by dating the center of randomly selected grains. However, this technique awaits application to apatite, which may prove challenging due to the lower He gas production in this mineral compared to zircon.…”

Badly Behaved Detrital (U‐Th)/He Ages: Problems With He Diffusion Models or Geological Models?

“…Quantitative analysis of this dispersion requires that it can be mapped, which in turn requires collecting tens of crystal ages as opposed to three to five crystal ages per sample, as required for inferring time‐temperature paths from broken crystals (Beucher et al, ; Brown et al, ). A promising approach the rapid acquisition of apatite (U‐Th)/He ages required to map the dispersion is to measure U, Th, and He in situ, negating several time‐consuming steps (Evans et al, ; Tian et al, ; Tripathy‐Lang et al, ; Vermeesch et al, ). An alternative approach is to gain as much data constraining the time temperature history of individual crystals either through dating the same crystal with multiple thermochronometric systems (Thomson et al, ) or through mapping the spatial distribution of helium using 4 He/ 3 He thermochronometry (Shuster & Farley, ) or in situ methods (Danišík et al, ).…”

A cirkon (U-Th)/He kormeghatározás módszertani alapjai és alkalmazása fiatal (<1 Ma) vulkánkitörések datálására

“…: TRIPATHY-LANG et al 2013. Felpolírozott szemcséken zajlik a mérés, így lehetséges előzetesen katódlumineszcens képeket is készíteni a vizsgált kristá lyokról, ezáltal megismerhetővé válik a belső felépítése a datált kristálynak.…”

“…Ennek kü lö -nösen a sziliciklasztos üledékek származáselem zé sé nél van nagy jelentősége. Hátránya az in situ eljárás nak, hogy a meg mért anyag kis mennyiségéből következően a mé rési adatok bizonytalansága, szórása jóval nagyobb, mint a konvencionális módszernél megszokott értékek (TRIPATHY-LANG et al 2013). Továbbá fiatal, tehát kis He-tartalmú minták mérése esetén gondot okozhat az, hogy nem a teljes kristály kigázosítása történik meg, hanem csak egy jóval kisebb térfogat He-tartalmát méri, amely jó eséllyel a műszer kimutatási határánál kevesebb 4 He-ot tartalmaz.…”