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.

References

[1] D.T. Aldiss. Plagiogranites from the ocean crust and ophiolites. Nature, 289 (1981), pp. 577-578,

[2] F.F. Basta, A.E. Maurice, B.R. Bakhit, K.A. Ali, W.I. Manton. Neoproterozoic contaminated MORB of Wadi Ghadir ophiolite, NE Africa: Geochemical and Nd and Sr isotopic constraints. Journal of African Earth Sciences, 59 (2011), pp. 227-242,

[3] H. Chen, Z. Tian, B. Tuller-Ross, R.L. Korotev, K. Wang. High-precision potassium isotopic analysis by MC-ICP-MS: an inter-laboratory comparison and refined K atomic weight. J Anal at Spectrom, 34 (2019), pp. 160-171,

[4] H. Chen, X.M. Liu, K. Wang. Potassium isotope fractionation during chemical weathering of basalts. Earth Planet Sci Lett, 539 (2020), Article 116192,

[5] R.G. Coleman, Z.E. Peterman. Oceanic plagiogranite. J Geophys Res, 80 (1975), pp. 1099-1108,

[6] P.A. Flagler, J.G. Spray. Generation of plagiogranite by amphibolite anatexis in oceanic shear zones. Geology, 19 (1991), pp. 70-73,

[7] P.A. Floyd, M.K. Yaliniz, M.C. Goncuoglu. Geochemistry and petrogenesis of intrusive and extrusive ophiolitic plagiogranites, Central Anatolian Crystalline Complex, Turkey. Lithos, 42 (1998), pp. 225-241,

[8] L. France, J. Koepke, B. Ildefonse, S.B. Cichy, F. Deschamps. Hydrous partial melting in the sheeted dike complex at fast spreading ridges: Experimental and natural observations. Contributions to Mineralogy and Petrology, 160 (2010), pp. 683-704,

[9] H. Gamaleldien, Z.-X. Li, Y. Kil, T. Abu-Alam. Origin of arc magmatic signature: A temperature-dependent process for trace element (re)-mobilization in subduction zones. Sci Rep, 9 (2019), p. 7098,

[10] H. Gamaleldien, L.S. Doucet, J.B. Murphy, Z.-X. Li. Geochemical evidence for a widespread mantle re-enrichment 3.2 billion years ago: implications for global-scale plate tectonics. Sci Rep, 10 (2020),

[11] H. Gamaleldien, Z. Li, M. Abu, J.B. Murphy, L.S. Doucet. Geochronological and isotopic constraints on Neoproterozoic crustal growth in the Egyptian Nubian Shield: Review and synthesis. Earth Sci Rev, 235 (2022), Article 104244,

[12] H. Gamaleldien, L.G. Wu, H.K.H. Olierook, C.L. Kirkland, U. Kirscher, Z.X. Li, T.E. Johnson, S. Makin, Q.L. Li, Q. Jiang, S.A. Wilde, X.H. Li. Onset of the Earth’s hydrological cycle four billion years ago or earlier. Nat Geosci, 17:6 (17) (2024), pp. 560-565,

[13] M. Hille, Y. Hu, T.Y. Huang, F.Z. Teng. Homogeneous and heavy potassium isotopic composition of global oceans. Sci Bull, 64 (2019), pp. 1740-1742,

[14] Y. Hu, F.Z. Teng, T. Plank, C. Chauvel. Potassium isotopic heterogeneity in subducting oceanic plates. Sci Adv, 6 (49) (2020), Article eabb2472,

[15] T.Y. Huang, F.Z. Teng, R.L. Rudnick, X.Y. Chen, Y. Hu, Y.S. Liu, F.Y. Wu. Heterogeneous potassium isotopic composition of the upper continental crust. Geochim Cosmochim Acta, 278 (2020), pp. 122-136,

[16] T.-Y. Huang, F.-Z. Teng, Z.-Z. Wang, Y.-S. He, Z.-C. Liu, F.-Y. Wu. Potassium isotope fractionation during granitic magmatic differentiation: Mineral-pair perspectives. Geochim Cosmochim Acta, 343 (2023), pp. 196-211,

[17] T.E. Johnson, C.L. Kirkland, Y. Lu, R.H. Smithies, M. Brown, M.I.H. Hartnady. Giant impacts and the origin and evolution of continents. Nature, 608 (2022), pp. 330-335,

[18] Kemp, A.I.S., Hawkesworth, C.J., 2014. Growth and Differentiation of the Continental Crust from Isotope Studies of Accessory Minerals, in: Treatise on Geochemistry. Elsevier, pp. 379–421. Doi:

[19] C.L. Kirkland, T.E. Johnson, J. Gillespie, L. Martin, K. Rankenburg, J. Kaempf, C. Clark. Bimodality in zircon oxygen isotopes and implications for crustal melting on the early Earth. Earth Planet Sci Lett, 625 (2024), Article 118491,

[20] J. Koepke, S.T. Feig, J. Snow, M. Freise. Petrogenesis of oceanic plagiogranites by partial melting of gabbros: An experimental study. Contributions to Mineralogy and Petrology, 146 (2004), pp. 414-432,

[21] W.W. Kuhnel, S.B. Jacobsen, Y. Li, Y. Ku, M.I. Petaev, S. Huang, Z. Wu, K. Wang. High-Temperature Inter-Mineral Potassium Isotope Fractionation: Implications for K-Ca-Ar Chronology. ACS Earth Space Chem, 5 (2021), pp. 2740-2754,

[22] W. Li, X.M. Liu, K. Wang, J. McManus, B.A. Haley, Y. Takahashi, M. Shakouri, Y. Hu. Potassium isotope signatures in modern marine sediments: Insights into early diagenesis. Earth Planet Sci Lett, 599 (2022), Article 117849,

[23] W. Li, L.A. Coogan, K. Wang, Y. Takahashi, M. Shakouri, Y. Hu, X.-M. Liu. Hydrothermal origin of heavy potassium isotope compositions in altered oceanic crust: Implications for tracing the elemental cycle. Earth Planet Sci Lett, 625 (2024), Article 118448,

[24] H. Liu, K. Wang, W.D. Sun, Y. Xiao, Y.Y. Xue, B. Tuller-Ross. Extremely light K in subducted low-T altered oceanic crust: Implications for K recycling in subduction zone. Geochim Cosmochim Acta, 277 (2020), pp. 206-223,

[25] J.F. Ma, X.L. Wang, A.Y. Yang, T.P. Zhao. Tracking Crystal-Melt Segregation and Accumulation in the Intermediate Magma Reservoir. Geophys Res Lett, 50 (2023), pp. e2022G-L102540,

[26] W.F. McDonough, S. Sun. The composition of the Earth. Chem Geol, 120 (1995), pp. 223-252,

[27] C.A. Parendo, S.B. Jacobsen, K. Wang. K isotopes as a tracer of seafloor hydrothermal alteration. Proc Natl Acad Sci, 114 (2017), pp. 1827-1831,

[28] C.A. Parendo, S.B. Jacobsen, J.I. Kimura, R.N. Taylor. Across-arc variations in K-isotope ratios in lavas of the Izu arc: Evidence for progressive depletion of the slab in K and similarly mobile elements. Earth Planet Sci Lett, 578 (2022), Article 117291,

[29] J.R. Reimink, T. Chacko, R.A. Stern, L.M. Heaman. Earth’s earliest evolved crust generated in an Iceland-like setting. Nat Geosci, 7 (2014), pp. 529-533,

[30] Rudnick, R.L., Gao, S., 2014. Composition of the Continental Crust, in: Treatise on Geochemistry. Elsevier, pp. 1–51. Doi:

[31] D.P. Santiago Ramos, L.A. Coogan, J.G. Murphy, J.A. Higgins. Low-temperature oceanic crust alteration and the isotopic budgets of potassium and magnesium in seawater. Earth Planet Sci Lett, 541 (2020), Article 116290,

[32] D.P. Santiago Ramos, S.G. Nielsen, L.A. Coogan, P.P. Scheuermann, W.E. Seyfried, J.A. Higgins. The effect of high-temperature alteration of oceanic crust on the potassium isotopic composition of seawater. Geochim Cosmochim Acta, 339 (2022), pp. 1-11,

[33] R.H. Smithies, Y. Lu, C.L. Kirkland, T.E. Johnson, D.R. Mole, D.C. Champion, L. Martin, H. Jeon, M.T.D. Wingate, S.P. Johnson. Oxygen isotopes trace the origins of Earth’s earliest continental crust. Nature, 592 (2021), pp. 70-75,

[34] Y. Sun, F.Z. Teng, Y. Hu, X.Y. Chen, K.N. Pang. Tracing subducted oceanic slabs in the mantle by using potassium isotopes. Geochim Cosmochim Acta, 278 (2020), pp. 353-360,

[35] F.Z. Teng, Y. Hu, J.L. Ma, G.J. Wei, R.L. Rudnick. Potassium isotope fractionation during continental weathering and implications for global K isotopic balance. Geochim Cosmochim Acta, 278 (2020), pp. 261-271,

[36] K. Wang, H.G. Close, B. Tuller-Ross, H. Chen. Global Average Potassium Isotope Composition of Modern Seawater. ACS Earth Space Chem, 4 (2020), pp. 1010-1017,

[37] K. Wang, S.B. Jacobsen. An estimate of the Bulk Silicate Earth potassium isotopic composition based on MC-ICPMS measurements of basalts. Geochim Cosmochim Acta, 178 (2016), pp. 223-232,

[38] Z.Z. Wang, F.Z. Teng, F.Y. Wu, Z.C. Liu, X.C. Liu, S.A. Liu, T.Y. Huang. Extensive crystal fractionation of high-silica magmas revealed by K isotopes. Sci Adv, 8 (2022), p. eabo4492,

[39] M. Zimmer, A. Kröner, K.P. Jochum, T. Reischmann, W. Todt. The Gabal Gerf complex: A precambrian N-MORB ophiolite in the Nubian Shield, NE Africa. Chem Geol, 123 (1995), pp. 29-51,