Oxygen isotopic alteration rate of continental crust recorded by detrital zircon and its implication for deep-time weathering.

• Oxygen isotope alteration rate of continental crust retrieved from zircon record. • Oxygen isotope alteration rate of continental crust is controlled by weathering. • Weathering history is linked to major evolution events of the Earth system. Weathering plays a significant role in the Earth system through the exchange of material among the lithosphere, atmosphere, hydrosphere, and biosphere. Variation of continental weathering in deep-time, however, remains elusive. This work investigates continental weathering recorded by detrital zircon. Zircon can record the oxygen isotopic composition (δ 18 O) of its parent crust at the time of crystallization, the value of which principally reflects the time-integrated effect of crustal alteration. The Hf isotopes and U-Pb isotopes of zircon also help to constrain the alteration history between crust generation and zircon crystallization. A new algorithm is introduced to reconstruct the average δ 18 O alteration rate of continental crust (R δ 18O-CC) through time by solving a set of linear equations based on a large population of detrital zircons with varying temporal coverage across the history of crustal alteration. A nearly three-billion-year history of R δ 18O-CC from 3.2 Ga to 0.3 Ga can be reconstructed using more than 5,000 globally distributed detrital zircons with coupled U-Pb-Hf-O isotopic records. The reconstructed R δ 18O-CC shows an overall bell-shape long-term evolution centered at ∼2 Ga superposed with variations that are coupled with supercontinental assembly cycles. The long-term evolution of the reconstructed R δ 18O-CC seems to be correlated with solid-earth CO 2 degassing expected from the age distribution of deleted mantle and the supercontinental cycles. Thus, the R δ 18O-CC is interpreted to reflect weathering considering the control of solid-earth CO 2 degassing on the total weathering flux of continental crust. However, independent evidence on the solid-earth CO 2 degassing is unavailable, interpreting R δ 18O-CC as a weathering record requires further testing. Nevertheless, this work provides an example of how the time-integrated signal, with large noise-to-signal ratio, preserved in geological archives can be deconvolved using a large dataset. The result also demonstrates the great potential that weathering history may have in reconstructing the operation of the Earth system across deep-time. [ABSTRACT FROM AUTHOR]