History of crustal growth in Africa and the Americas from detrital zircon and Nd isotopes in glacial diamictites

• Published in: Precambrian research 2022-06, Vol.373, p.106641, Article 106641
• Main Authors: Gaschnig, Richard M., Horan, Mary F., Rudnick, Roberta L., Vervoort, Jeffrey D., Fisher, Christopher M.
• Format: Article
• Language: English
• Subjects: Continental crust; Detrital zircon; Glaciation; Hafnium isotopes; Neodymium isotopes; Provenance
• ISSN: 0301-9268; 1872-7433
• DOI: 10.1016/j.precamres.2022.106641

•Detrital zircon age and Hf isotope and whole-rock Nd isotope data are provided for Mesoarchean, Paleoproterozoic, Neoproterozoic, and Paleozoic glacial diamictites from around the world.•Hf and Nd isotope data record major episodes of crustal growth at 3.2, 2.8–2.7, 2.0–1.7, and 1.3–0.9 Ga,•Zircons older than 3.6 Ga are completely absent, as is Hf and Nd isotope evidence for reworking of greater than 3.6 Ga continental crust; such crust appears to have been rare. Diamictites produced by continental glaciations were deposited in the Mesoarchean (∼2.9 Ga), Paleoproterozoic (∼2.4–2.2 Ga), Neoproterozoic (∼0.75–0.58 Ga), and Paleozoic (∼0.3 Ga), and, with the exception of the Mesoarchean, occur on multiple modern continents. We examine the provenance of a selection of these diamictites from all four time periods and three continents via detrital zircon U-Pb geochronology and Hf isotope and whole-rock Nd isotope analyses. Mesoarchean samples from South Africa contain mostly Mesoarchean zircon, with a much smaller number of Paleoarchean grains. Zircon Hf and whole-rock Nd point towards their derivation from reworked Paleoarchean crust. Paleoproterozoic samples from North America share a similar unimodal zircon age distribution, with a peak at 2.7 Ga and a narrow range in Hf isotopes that is slightly superchondritic. Coupled with whole-rock Nd results, these data point to their derivation from reworked juvenile Mesoarchean crust. By contrast, the Nd isotope data and existing published detrital zircon U-Pb data for Paleoproterozoic diamictites from South Africa indicate a mix of Neoarchean and Mesoarchean sources. Neoproterozoic samples from Namibia share a Paleoproterozoic detrital zircon population with variable but subchondritic Hf isotope compositions, indicating derivation from reworked Neoarchean crust. Most samples also have Mesoproterozoic and Neoproterozoic zircon with both positive and negative εHf(i), and all have Nd isotope compositions yielding Paleoproterozoic model ages. A Neoproterozoic sample from Canada contains mostly Neoproterozoic detrital zircon with variable Hf isotope compositions, indicating a mix of juvenile and reworked Mesoproterozoic crust. Samples from different parts of the Paleozoic Dwyka Group in South Africa show significantly different provenance, with a western locality containing only zircon older than 2.0 Ga and a Neoarchean Nd model age. By contrast, eastern samples have Paleoproterozoic model ages and published detrital zir