META-ANALYSIS OF GLOBAL DETRITAL ZIRCON REVEALS BIAS BETWEEN MODERN AND ANCIENT SEDIMENTS

Detrital zircon have long been the hallmark for identifying sedimentary provenance and tracing magmatism through geologic time. The compilation of global datasets has been used to evaluate and constrain the secular change of geologic processes. As these database grow, it is assumed that the representative nature of our samples increases. However, recent work has shown that significant biases exists at multiple levels from zircon formation (magmatic bias), exhumation (tectonic bias), weathering (compositional bias), transport (sedimentary bias), dispersal (geographic bias), and temporal perpetuation (preservation bias). These biases make it difficult to decide how to truly arrive at a representative dataset.

Using a newly compiled zircon database, we identify a significant bias between modern and ancient sediments. We further argue that if we are to arrive at a database that is representative of extant crust, modern sediments provide the most straightforward and logical repository of a continental archive. While the evolution of the continental crust may be afforded through ancient sedimentary deposits, they do not capture the crust that formed in “modern” tectonic settings. Furthermore, by combining the zircon data from modern sediment with ancient sedimentary rocks, we preferentially bias older crust.

When evaluating crustal recycling through time using zircon U-Pb and Hf, the exclusion of zircon derived from ancient sedimentary rocks results in a shallower cumulative crustal recycling curve implying greater crustal reworking than previous estimates. This effect is further magnified when the spatial bias is removed by normalizing the data from individual modern river catchments. The cumulative crustal recycling curves of modern river catchments that drain active convergent margins demonstrate disproportionate recycling of Proterozoic mobile belts while Archean cratons are insulated from further reworking. This may imply the supercontinental preservation bias is restricted to post-Archean time.