22-EPN3-093: The Origin of Metal-Rich Brine Component in the Ontong Java Plateau Magmas – Ion Probe Study of Boron Isotopes and Halogen Abundances in Volcanic Glasses
Virtual visit by Maxim Portnyaginy of the GEOMAR Helmholtz Centre for Ocean Research Kiel (Germany) to TA2.9 Ion Probe Facility (IPF), CRPG (France)
Dates of visit: 4-8 December 2023
Report Summary: We used a multi-collector ion probe CAMECA IMS 1270-E7 at CRPG, Nancy, to analyse boron isotope composition and bromine concentrations in a representative set of 20
Ontong Java Plateau volcanic glasses. The visit was virtual on agreement with the host lab.
The results were achieved within the granted period of analytical time. The data revealed wide variations d11B in glasses from –8.6 ‰ to +12.6 ‰. Strong correlations were found between d11B and Cl/K (positive correlation) and between d11B and K/B (negative correlation). The concentrations of Br in the OJP glasses were found to range from 0.9 to 8.3 ppm. The Br contents correlate strongly with Cl contents so that the Br/Cl ratio in glasses is relatively constant and ranges between 3.1–4.9×10-3. The new data allowed us to propose three possible alternative scenarios for the origin of halogen- and metal-rich
component involved in OJP magmatism, which are following: (1) the magmas might have assimilated seawater-derived salt with lower δ11 B than that of the seawater, (2) the magmas assimilated initially high-δ11 B and high Br/Cl brines, which might have changed their compositions to lower values due to interaction with low-δ11 B and low Br/Cl crustal rocks before interaction with OJP magmas, and (3) the magmas assimilated brines derived from seawater with lower δ11 B during the Cretaceous than that of the modern seawater. The hypotheses will be elaborated in future studies.
