Webbläsaren som du använder stöds inte av denna webbplats. Alla versioner av Internet Explorer stöds inte längre, av oss eller Microsoft (läs mer här: * https://www.microsoft.com/en-us/microsoft-365/windows/end-of-ie-support).

Var god och använd en modern webbläsare för att ta del av denna webbplats, som t.ex. nyaste versioner av Edge, Chrome, Firefox eller Safari osv.

Sanna

Sanna Alwmark

Biträdande universitetslektor

Sanna

Radioisotopic age constraints of the Cambrian Ritland impact structure, Norway

Författare

  • William R. Hyde
  • Steven J. Jaret
  • Gavin G. Kenny
  • Anders Plan
  • Elias J. Rugen
  • Martin J. Whitehouse
  • Sanna Alwmark

Summary, in English

Secondary ion mass spectrometry U-Pb geochronology has been performed on zircon grains separated from impact melt rock from the 2.7 km-in-diameter Ritland impact structure, southwestern Norway. Scanning electron microscope-based imaging techniques, including electron backscatter diffraction analysis, reveal various zircon grain microtextures, including shock-recrystallization and high-temperature zircon decomposition. Analyses from unshocked zircon grains yield two distinct concordant age populations at 1.5 and ~2.5 Ga, interpreted to represent igneous crystallization ages. The former aligns with Telemarkian magmatism (1.52–1.48 Ga) which dominates the local area of the Sveconorwegian orogeny and the target sequence at Ritland. The latter indicates a more ancient zircon population in Southern Norway, representing detrital grains in cover sediments present at the time of impact in the Cambrian. Collectively, the U-Pb data form two distinct discordant arrays with poorly resolved lower intercept ages spanning the Cambro-Ordovician boundary. The melt rock at Ritland is highly altered, and significant postimpact Pb loss is observed throughout the U-Pb data, likely in response to burial-induced thermal overprinting during the Caledonian orogeny. Post-filtering and selection of the data to minimize the effects of nonimpact-specific Pb loss, the two discordia produce indistinguishable lower intercept ages of 586 ± 73 Ma (MSWD 1.6, n = 15) and 545 ± 48 Ma (MSWD = 11, n = 9) which coincide in the Cambrian–Late Ediacaran. We therefore provide radioisotopic support for previous stratigraphic age constraints for the formation of the structure (500–542 Ma).

Avdelning/ar

  • Geologiska institutionen

Publiceringsår

2025-08-14

Språk

Engelska

Sidor

2223-2238

Publikation/Tidskrift/Serie

Meteoritics and Planetary Science

Volym

60

Avvikelse

9

Dokumenttyp

Artikel i tidskrift

Förlag

Wiley-Blackwell

Ämne

  • Geology

Aktiv

Published

ISBN/ISSN/Övrigt

  • ISSN: 1086-9379