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Boron isotopic analysis of Oceanic deposits as a recorder of Continental emergence in the Archean

The onset of plate tectonics on Earth brought about rapid accumulation of continental crust, and the transition of continental crust from being mostly submarine to mostly subaerial. Tracking the timing and rate of continental emergence has broad implications on the onset of plate tectonics and to our understanding of its operation in its early days. Different approaches to study and trace continental emergence address the continental crust itself, whether in specific localities or in compilation of large datasets. Such approaches may be challenged as such that either represent local activity rather than the global regime, or that they might suffer from various kinds of biases. We attempt to overcome some of these shortcomings by utilizing Boron isotopic analysis of Archean and Proterozoic Oceanic sediments. Boron is a continental element that is concentrated in the continental crust over time. The Oceanic Boron budget is mostly controlled by the balance between influx from continental weathering carried by rivers and the out-flux during alteration of Oceanic crust. The onset of widespread continental emergence means the largest Boron influx into the Ocean begins to operate, thus greatly affecting the Oceanic B concentration and isotopic budget. We analyzed samples of Archean and Proterozoic Chert and Iron Formations for B isotopes using in-situ LA-MC-ICP-MS in order to construct the Oceanic Boron isotopic record from that time. Considering the fractionation between seawater and silica/Fe-oxides we observe that Archean seawater was 10-20‰ lighter than modern seawater, indicating a lower volume of emerged continental crust.


Avishai Abbo1, Horst Marschall1, Axel Gerdes1
1Goethe University Frankfurt, Germany
GeoMinKöln 2022