PROXIMAL TONIAN SOURCES OBVIATE NEED FOR PAN-LAURENTIAN RIVERS TO EXPLAIN “GRENVILLIAN” DETRITAL ZIRCON

We re-evaluate the provenance of Mesoproterozoic detrital zircons in western Laurentia, challenging the long-held notion of their transport from the Grenville orogen via a massive transcontinental fluvial system. This interpretation overlooks critical geological evidence that favours more proximal sources and processes.

Firstly, Hf isotopic signatures of detrital zircon east and west of the Transcontinental Arch are distinctly different according to quantitative comparison of bivariate kernel density estimates, undermining the hypothesis of Grenville detritus being transported across this feature. Secondly, numerous Stenian-aged magmatic sources in western Laurentia, including the Llano Uplift, Pikes Peak batholith, and the southwestern Laurentia large igneous province, provide plausible proximal contributors for the observed zircons. Lastly, the similarity between Tonian and Stenian U-Pb zircon age distributions in northern Laurentian strata increases significantly after the Devonian. This timing corresponds to the late-Paleozoic draining of western Laurentia and the westward flushing of Grenville detritus across the Transcontinental Arch.

These observations suggest that post-Devonian dispersal processes better explain the distribution of Grenville-aged detritus, negating the need for a Proterozoic transcontinental river system. We conclude that Tonian zircons in western Laurentia are plausibly derived from more proximal sources and later sedimentary redistribution.