DOMINANCE AND PERSISTENCE OF THE GRENVILLE MAGMATIC SIGNATURE IN THE DETRITAL ZIRCON RECORD: INSIGHT INTO EXHUMATION OF THE GRENVILLE OROGEN AND POTENTIAL TECTONIC INTERACTION OF LAURENTIA AND AMAZONIA DURING GRENVILLIAN COLLISION

A virtual ‘mountain’ of detrital zircon (DZ) U-Pb ages for late Mesoproterozoic to modern sediments demonstrate the dominance and persistence of Grenvillian DZ in Laurentian clastic systems. The dominance reflects the size of the orogen, and the volume and zircon fertility of Grenvillian magmatic phases: major Shawinigan (Geon 11) and Ottawan (Geon 10); moderate Elzevirian (late Geon 12) and pre-Elzevirian (late Geon 13); and minor Rigolet (early Geon 9). ⁴⁰Ar-³⁹Ar ages show the Grenville orogen began exhuming 1.1-1.0 Ga with slow exhumation through ~0.6 Ga. Ottawan and some Shawinigan orogenic crust could not have been fully exhumed until the latest Neoproterozoic. Latest Mesoproterozoic and earliest Neoproterozoic Laurentian clastic sequences are dominated by Geon 13, 12, and 11 age modes with insignificant Geon 10; variable Geon 14 from the Granite Rhyolite province; and variable 1100 Ma ages from bimodal Midcontinent Rift magmatism. Latest Neoproterozoic clastic sequences are dominated by Geons 13-9, representing the final emergence of the full Grenville DZ signature. The persistence of Grenville dominance attests to the enormous amount of sediment eroded from the exhuming Grenville orogen from 1.1 to 0.7 (the Great Grenvillian Sedimentation Event: GGSE) that was reworked during formation of the Great Unconformity. Basal Cambrian sequences along the Laurentian margin reworked the Neoproterozoic sediments and likewise exhibit the Grenville DZ signature. Sequential Phanerozoic sequences repeatedly recycle Grenville DZ. In contrast, cratonic western Amazonia (W. Brazil), which collided with southeast Laurentia during the Grenville orogeny, lacks DZ evidence for a continental-scale GGSE. However, the proto-Andean margin buried beneath the Andean clastic wedge (ACW) in Peru, and modern Amazon R. fluvial systems, do show Grenvillian dominance. This is interpreted as Grenvillian orogenic crust being more extensive beneath the ACW and/or spillover of sediment from southeastern Laurentia onto westernmost Amazonia. The Sunsás Province of western Amazonia is not a significant source for Grenvillian DZ: it is a low volume magmatic event and does not include the full range and proportion of Geon 13-9 magmatic rocks apparent in DZ age distributions from the Andean basement and Amazon River fluvial systems.