Oxygen isotopes in cherts record paleo−heat flow on Shatsky Rise (western Pacific Ocean)

Sedimentary cherts form from amorphous silica precursors that progressively crystallize into opal-CT and quartz during burial diagenesis. Recent studies have shown that the transformation kinetics of the silica polymorphs strongly depend on the prograde thermal history, suggesting a key role of basal heat flow in setting the 18O/16O and 17O/16O 18O/16O oxygen isotope ratios in chert (δ18Ochert, Δ′17Ochert). To investigate the relationship between paleo−heat flow and chert oxygen isotopes, we used Cretaceous to Neogene cherts that formed in the large igneous province Shatsky Rise in the western Pacific Ocean and a compilation of marine chert oxygen isotope ratios from previous studies. Using a reaction-advection-diffusion model, we demonstrate that the relationship between δ18Ochert, Δ′17Ochert, and the age of the underlying crust results from declining heat flow through sediment as the oceanic crust cools. Our reconstruction of heat flow at Shatsky Rise aligns with established geothermal background values. We propose that the Archean chert record indicates a diagenetic environment dominated by high heat flow that transitioned on billion-year time scales toward conditions resembling modern diagenesis.