Tracing the emergence and evolution of Continental Crust in the Archean–Proterozoic using in-situ B isotopic analysis of Oceanic deposits

• Applicant: Dr. Avishai Abbo
• Subject Area: Mineralogy, Petrology and Geochemistry ; Geology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 539548092

The growth and accumulation of continental crust on Earth through time is a contested topic in Earth Science research, with implications on the onset of modern-style plate tectonics and its operation over different periods of the geologic record. Tracing crustal growth in the Early Earth from the fragments of preserved Archean-Proterozoic crust may carry biases related to preservation and difficulty in establishing a global regime from local or regional datasets, while in large global datasets it is nearly impossible to account for the equal validity and/or significance of every single point. Here I propose to trace the accumulation of continental crust on Earth, and specifically its exposure and emergence above sea-level, by monitoring boron isotopes in Archean-Proterozoic oceanic deposits – cherts and Iron Formations (IFs). Boron in the oceanic system is sourced mostly from continental erosion and consumed mainly through alteration of oceanic crust. Processes of continental crustal buildup and exposure will bear impact on the oceanic composition, which will in turn be preserved in the marine sediments I will analyze. As boron behaves conservatively and is completely mixed in seawater over ca. 10^3 years, the boron signal recorded in chemical oceanic deposits is a good indication of the global regime. Cherts and IFs are chemical marine deposits, precipitated directly from seawater, thus serving as an archive of oceanic chemistry. In the absence of exposed continental crust above sea-level, the ocean is expected to have a very low boron concentration in equilibrium with the oceanic crust or mantle. With increasing exposure and continental emergence, boron concentrations and isotopic composition of the ocean are expected to slowly approach modern values. Accounting for the different fractionation factors between seawater and silica/Fe-oxide, my new data will enable to establish oceanic boron elemental and isotopic evolution curves for the Archean-Proterozoic. Time dependent modelling accounting for the different boron inputs and outputs to and from the ocean should allow me to quantify the best fitting set of conditions, rising from obtained data, as for the extent of continental emergence, its timing, and the interplay between continental buildup and oceanic crust production through time. The proposed study will therefore tackle the question of crustal growth through time in a novel, revolutionary and underexplored fashion, and will provide a significant contribution to the study of crustal evolution, the onset of plate tectonics, and boron isotopes in the oceanic environment.

• DFG Programme: Research Grants