Potassium isotopes trace the formation of juvenile continental crust

Abstract

Constraining the processes associated with the formation of new (juvenile) continental crust from mantle-derived (basaltic) sources is key to understanding the origin and evolution of Earth’s landmasses. Here we present high-precision measurements of stable isotopes of potassium (K) from Earth’s most voluminous plagiogranites, exposed near El-Shadli in the Eastern Desert of Egypt. These plagiogranites exhibit a wide range of δ⁴¹K values (–0.31‰ ± 0.06‰ to 0.36‰ ± 0.05‰; 2 SE, standard error) that are significantly higher (isotopically heavier) than mantle values (–0.42‰ ± 0.08‰). Isotopic (⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd) and trace element data indicate that the large variation in δ⁴¹K was inherited from the basaltic source rocks of the El-Shadli plagiogranites, consistent with an origin through partial melting of hydrothermally-altered mid-to-lower oceanic crust. These data demonstrate that K isotopes have the potential to better constrain the source of granitoid rocks and thus the secular evolution of the continental crust.

Keywords

Potassium isotopes / Plagiogranites / Arabian–Nubian Shield / Neoproterozoic / Crustal growth

CRediT authorship contribution statement

Hamed Gamaleldien: Conceptualization, Data curation, Funding acquisition, Investigation, Methodology, Writing – original draft. Kun Wang: Formal analysis, Funding acquisition, Methodology, Writing – review & editing. Tim E. Johnson: Investigation, Writing – review & editing. Jian-Feng Ma: Methodology, Writing – review & editing. Mohamed Abu Anbar: Investigation, Methodology. Xinmu J. Zhang: Formal analysis. Hugo K.H. Olierook: Investigation, Writing – review & editing. Christopher L. Kirkland: Investigation, Writing – review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

H.G. thanks Z-X Li for assistance during fieldwork. We thank the Editorial Advisor Prof. M. Santosh, Associate Editor Dr. S. Glorie, and two anonymous reviewers for their comments. H.G. acknowledges funding from the Khalifa University start-up fund (8474000697/FSU-2024-006). K.W. acknowledges support from the McDonnell Center for the Space Sciences and NASA (Emerging Worlds Program Grant No. #80NSSC21K0379). T.E.J. acknowledges funding from the Australian Government through an Australian Research Council Discovery Project (DP200101104). This is a contribution to IGCP 648: Supercontinent Cycles and Global Geodynamics.

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