Oxygen isotope (δ18O, Δ′17O) insights into continental mantle evolution since the Archean

Oxygen isotopic ratios are largely homogenous in the bulk of Earth's mantle but are strongly fractionated near the Earth's surface, thus these are robust indicators of recycling of surface materials to the mantle. Here we document a subtle but significant similar to 0.2 parts per thousand temporal decrease in delta O-18 in the shallowest continental lithospheric mantle since the Archean, no change in Delta'O-17 is observed. Younger samples document a decrease and greater heterogeneity of delta O-18 due to the development and progression of plate tectonics and subduction. We posit that delta O-18 in the oldest Archean samples provides the best delta O-18 estimate for the Earth of 5.37 parts per thousand for olivine and 5.57 parts per thousand for bulk peridotite, values that are comparable to lunar rocks as the moon did not have plate tectonics. Given the large volume of the continental lithospheric mantle, even small decreases in its delta O-18 may explain the increasing delta O-18 of the continental crust since oxygen is progressively redistributed by fluids between these reservoirs via high-delta O-18 sediment accretion and low-delta O-18 mantle in subduction zones.