Eoarchaean crustal evolution of the North Atlantic craton

• Main Authors: Lancaster, Penelope J., Storey, Craig D., Hawkesworth, Chris J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2011
• Subjects: /dk/atira/pure/core/subjects/earthsci; Earth Sciences; North Atlantic
• Online Access: https://researchportal.port.ac.uk/portal/en/publications/eoarchaean-crustal-evolution-of-the-north-atlantic-craton(3dbae5a5-f2d2-489c-8f33-e25637d182cb).html; https://researchportal.port.ac.uk/ws/files/1429736/Lancaster_2011.doc; http://minmag.geoscienceworld.org/content/75/3/1261.full.pdf+html

Recent studies suggest extraction of juvenile crust from the mantle has been globally continuous throughout Earth’s history, but the crustal record is biased by preservation, particularly from supercontinents [e.g. 1, 2]. As a result, crust older than the first supercontinent at c. 2.7 Ga is now rare and frequently strongly reworked. However, younger sedimentary rocks may preserve fragments of Archaean basement by sampling wide areas, including those which have since been buried or destroyed, thereby providing a more complete record of the ancient crust. Of these sedimentary rocks, coarse basal units are most likely to preserve local basement, constraining the likely geographical distribution of those source areas and providing greater context for any detrital material. Detrital zircons have been analyzed from basal units of the Meso/Neoproterozoic to Cambrian Stoer, Sleat, Ardvreck and Morar groups in NW Scotland to evaluate basement source ages and isotopic signatures. Widespread crustal extraction is recorded in Hf model ages between 4160–1410 Ma, peaking at c. 3350 Ma, with significant crystallisation and/or reworking between 3670–1070 Ma, peaking at c. 2700 Ma. Similar crystallisation and model ages have been identified around the North Atlantic Craton, suggesting a shared, but not consanguineous, origin. All four units contain Hf model ages that imply partial reworking of Eoarchaean crust, and model ages as old as 4200 Ma from the basal Ardvreck Gp. indicate the existence of much older crust in Scotland and the greater North Atlantic Craton. Such consistency around the craton reinforces the conclusion that crustal extraction and crystallisation are continuous, large-scale processes, and have been since the very earliest Earth.