Reworking subducted sediments in arc magmas and the isotopic diversity of the continental crust: The case of the Ordovician Famatinian crustal section, Argentina

• Published in: Earth and planetary science letters 2022-10, Vol.595, p.117706, Article 117706
• Main Authors: Cornet, J., Laurent, O., Wotzlaw, J.-F., Antonelli, M.A., Otamendi, J., Bergantz, G.W., Bachmann, O.
• Format: Article
• Language: English
• Subjects: continental arcs; continental evolution; Earth Sciences; Geochemistry; O-Hf/U-Pb isotopes; Petrography; recycling; reworking; Sciences of the Universe; source contamination; Volcanology
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2022.117706

•Zircon O-Hf isotopes and high-precision U-Pb zircon dating on a mafic to felsic suite of plutonic and volcanic samples.•Source vs. Path contamination naturally exposed along a 750 km N-S paleo-arc axis in the Famatinian arc, Argentina.•Sediment subduction alters the isotopic composition of source arc magmas during a major continent-forming magmatic event. Since the onset of plate tectonics, continents have evolved through a balance between crustal growth, reworking, and recycling at convergent plate margins. The term “reworking” involves the re-insertion of crustal material into pre-existing crustal volumes, while crustal growth and recycling respectively represent gains from and losses to the mantle. Reworking that occurs in the mantle wedge (“source” contamination from slab material) or within the upper plate (“path” contamination), will have contrasting effects on crustal evolution. However, due to limited access to deep crustal and mantle rocks, quantifying source vs. path contamination remains challenging. Based on the 4-dimensional record of the fossil (Ordovician) Famatinian continental arc (Argentina), we demonstrate that source contamination plays a dominant role in imprinting mafic to granitic rocks with crustal oxygen-hafnium (O-Hf) isotopic compositions. We argue that source contamination at convergent plate margins significantly increased the diversity of O-Hf isotopic signatures of continents over geologic time. Our interpretation implies that crustal evolution models attributing this isotopic diversity dominantly to intra-crustal reworking may be over-simplistic and may underestimate continental growth in the last 2.5 billion years.