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.

Anders Scherstén

Anders Scherstén

Universitetslektor

Anders Scherstén

Hafnium isotope evidence for a transition in the dynamics of continental growth 3.2Gyr ago

Författare

  • Tomas Naeraa
  • Anders Scherstén
  • M. T. Rosing
  • A. I. S. Kemp
  • J. E. Hoffmann
  • T. F. Kokfelt
  • M. J. Whitehouse

Summary, in English

Earth's lithosphere probably experienced an evolution towards the modern plate tectonic regime, owing to secular changes in mantle temperature(1,2). Radiogenic isotope variations are interpreted as evidence for the declining rates of continental crustal growth over time(3-5), with some estimates suggesting that over 70% of the present continental crustal reservoir was extracted by the end of the Archaean eon(3,5). Patterns of crustal growth and reworking in rocks younger than three billion years (Gyr) are thought to reflect the assembly and break-up of supercontinents by Wilson cycle processes and mark an important change in lithosphere dynamics(6). In southern West Greenland numerous studies have, however, argued for subduction settings and crust growth by arc accretion back to 3.8 Gyr ago(7-9), suggesting that modern-day tectonic regimes operated during the formation of the earliest crustal rock record. Here we report in situ uranium-lead, hafnium and oxygen isotope data from zircons of basement rocks in southern West Greenland across the critical time period during which modern-like tectonic regimes could have initiated. Our data show pronounced differences in the hafnium isotope-time patterns across this interval, requiring changes in the characteristics of the magmatic protolith. The observations suggest that 3.9-3.5-Gyr-old rocks differentiated from a >3.9-Gyr-old source reservoir with a chondritic to slightly depleted hafnium isotope composition. In contrast, rocks formed after 3.2 Gyr ago register the first additions of juvenile depleted material (that is, new mantle-derived crust) since 3.9 Gyr ago, and are characterized by striking shifts in hafnium isotope ratios similar to those shown by Phanerozoic subduction-related orogens(10-12). These data suggest a transitional period 3.5-3.2 Gyr ago from an ancient (3.9-3.5 Gyr old) crustal evolutionary regime unlike that of modern plate tectonics to a geodynamic setting after 3.2 Gyr ago that involved juvenile crust generation by plate tectonic processes.

Avdelning/ar

  • Berggrundsgeologi

Publiceringsår

2012

Språk

Engelska

Sidor

627-627

Publikation/Tidskrift/Serie

Nature

Volym

485

Issue

7400

Dokumenttyp

Artikel i tidskrift

Förlag

Nature Publishing Group

Ämne

  • Geology

Aktiv

Published

ISBN/ISSN/Övrigt

  • ISSN: 0028-0836