Long-lived radioactive isotopes provide valuable information on the evolution of Earth's geological reservoirs. Coupled measurements of the 138La-138Ce and 147Sm-143Nd systems have attracted much interest, but some critical reservoirs, such as the deep continental crust, have yet to be investigated. To address this gap, we report Ce-Nd isotope measurements of 35 crustal samples from Canada, western Europe, and Siberia, with Archean to Phanerozoic ages. Most samples from western Europe and Siberia are interpreted to represent the deepest continental crust because of low SiO2 content (< 55 wt%) and generally mafic compositions. In contrast, Precambrian composites from the Canadian shield have highly felsic compositions (61–71 wt% SiO2) and represent the old upper continental crust. Xenoliths from the Massif Central (France) and samples from uplifted massifs in the Ivrea-Verbano zone (Italy) plot on the Ce-Nd mantle array. Precambrian Canadian composites and xenoliths from Udachnaya (Siberian Craton) plot to the left of the mantle array, with the Siberian samples farthest from the array. The La-Ce system yields a ca. 1.8 Ga age for the Siberian xenoliths, distinct from the ca. 2.7 Ga Sm-Nd errorchron age. The La-Ce system was most likely reset during a large-scale episode of delamination and rejuvenation of the Archean lower lithosphere established in Siberia. A change in the La/Ce ratio during this event explains an increasing deviation with time of the Ce-Nd isotopic composition of the Siberian deep crust from the mantle array. We introduce a new parameter (θ) to quantify the likelihood of any rock evolving away from the mantle array. It represents the angle between the evolution vector of a sample and the mantle array, and it is calculated from measured La/Ce and Sm/Nd ratios. Samples that plot to the right of the mantle array have θ > 0, whereas samples that plot to the left of the mantle array have θ < 0. The angle θ was used to compare our samples to a worldwide granulite compilation (1581 samples) because it is independent of the age and the initial isotopic composition of the samples. The majority of lower crust rocks have negative θ, suggesting they are prone to evolve to the left of the mantle array, but to a lesser extent than the Siberian samples that are characterized by the most negative θ values. Thus, the Siberian samples with the most unusual Ce-Nd isotopic compositions are the only group to plot close to the deep crust end-member calculated from classical mass-balance budget of the bulk silicate Earth. These results suggest that the lower crust sampled by Siberian xenoliths is only a minor component in the terrestrial deep crust. We use this database to estimate new parent/daughter ratios for the lower continental crust: 138La/142Ce = 0.00380 ±0.00007 and 147Sm/144Nd = 0.128 ±0.007. Measurements and models are finally reconciled when considering massive recycling of lower continental crust through Earth's history, totaling 3 to 4 present-day, continental crust masses.
Authors
Claudine Israel, Maud Boyet, Régis Doucelance, Pierre Bonnand, B. Dhuime, D. Ionov, H. Moreira, M.G. Jackson, A.V. Golovin
- Bibliographic Reference
- Claudine Israel, Maud Boyet, Régis Doucelance, Pierre Bonnand, B. Dhuime, et al.. First Ce-Nd isotope measurements of middle and lower continental crust samples support massive lower crust recycling over Earth's history. Lithos, 2023, 460-461, pp.107369. ⟨10.1016/j.lithos.2023.107369⟩. ⟨hal-04300088⟩
- DOI
- https://doi.org/10.1016/j.lithos.2023.107369
- HAL Collection
- ['IRD - Institut de recherche pour le développement', "INSU - Institut National des Sciences de l'Univers", 'Université de Bretagne occidentale - Brest (UBO)', 'Université des Antilles', 'HAL-Francophonie, Afrique et océan indien', 'Université de Clermont', 'CNRS - Centre national de la recherche scientifique', 'Institut de Physique du Globe de Paris', 'Université Paris Cité', 'Géosciences Montpellier', 'Laboratoire Magmas et Volcans', 'ACL en Sciences fondamentales', 'Université de Montpellier', 'Observatoire de Physique du Globe de Clermont-Ferrand', 'I-Site CAP 20-25', 'ANR', 'Université de Montpellier (2015-2021)', 'Université de Montpellier - EPE']
- HAL Identifier
- 4300088
- Institution
- ["Institut national des sciences de l'Univers", 'Institut de Recherche pour le Développement et la société', 'Université de La Réunion', 'Institut de Physique du Globe de Paris', 'Université Paris Cité', 'Université de Brest', 'University of California [Santa Barbara]', 'Siberian Branch of the Russian Academy of Sciences']
- Laboratory
- ['Laboratoire Magmas et Volcans', 'Institut de Physique du Globe de Paris', 'Géosciences Montpellier', 'Department of Earth Science [Santa Barbara)', 'Sobolev Institute of Geology and Mineralogy [Novosibirsk]']
- Published in
- France
Table of Contents
- 0.022558 54
- 0.022563 54
- 0.022568 54
- 0.022573 54
- 0.022578 54
- 0.001 0.003 0.005 0.007 54
- Ce Ce 54
- La Ce 54
- Siberia 54
- This study Literature xenolith Kimberlite 54
- Age 1828 376 Ma n 15 MSWD 11 54
- 0.5100 54
- 0.5105 54
- 0.5110 54
- 0.5115 54
- 0.5120 54
- 0.5125 54
- 0.5130 54
- 0.5135 54
- 0.00 0.05 0.10 0.15 0.20 0.25 54
- Nd Nd 54
- Sm Nd 54
- Age 2730 268 Ma n 15 MSWD 28 54
- Africa 23 56
- 5 Antarctica 56
- 3 1 56
- Asia 56
- 132 30 56
- Australia 56
- 2 0 56
- Europe 98 22 56
- America 110 25 56
- S. America 56
- 11 2 56
- Siberia 66 15 56
- Africa 56
- 274 24 56
- Antarctica 56
- 0 0 56
- Asia 56
- 274 24 56
- Australia 33 3 56
- Europe 256 23 56
- America 201 18 56
- America 73 6 56
- Siberia 25 2 56
- 0.025 57
- 0.050 57
- 0.075 57
- 0.100 57
- 0.125 57
- 0.150 57
- 0.175 57
- 0.200 57
- 0.225 57
- 0.250 57
- 0.001 0.003 0.005 0.007 0.009 57
- Sm Nd 57
- La Ce 57
- 20 40 60 80 100 120 57
