The study overturns the assumption that oxygen isotopes in cherts directly reflect ancient climate conditions. Instead, the ratios of three oxygen isotopes-16O, 17O, and 18O-correlate with variations in geothermal heat flow across the seafloor. This insight offers scientists a new tool for reconstructing Earth's early thermal evolution.
Cherts analyzed from the Shatsky Rise oceanic plateau in the western Pacific, east of Japan, along with data from international drilling projects, reveal that isotope compositions shift with the amount of heat released from the underlying crust. Areas where magma has recently formed new crust show stronger heat flow, while older crust has cooled significantly.
Using a new calculation model, the researchers successfully determined how much heat once passed through Earth's crust, verifying their results with independent oceanic measurements. This marks the first time that paleo-heat flow has been directly quantified using oxygen isotope data in sedimentary rocks.
"Our method enabled us to measure - for the first time - how much heat flowed through the Earth's crust in the past and thus interpret and understand a piece of Earth's history," explains lead author Oskar Schramm, who conducted the study at Gottingen University's Geosciences Centre and now works at Ruhr University Bochum. Professor Michael Tatzel, who supervised the research, adds: "Next, we want to clarify why some cherts show unusual oxygen isotope patterns that were not in equilibrium with the seawater at the time they formed. Initial findings from our recent findings suggest that volcanic ash may play a crucial role."
Research Report:Oxygen isotopes in cherts record paleo-heat flow on Shatsky Rise (Western Pacific Ocean)
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