One of Earth's greatest mountain-building episodes, the Grenvillian orogeny, occurred with the assembly of the supercontinent Rodinia at the end of the Mesoproterozoic era, about 1.2-1.0 billion years ago. Weathering and erosion of the Grenvillian mountain chain, the roots of which can be traced today for nearly 12,000 km, produced huge volumes of sedimentary detritus that were dispersed by an enormous system of braided rivers. Erosion, denudation, and sediment throughput were enhanced by a lack of vegetation and vigorous continental weathering under a climate that favored strong chemical alteration. The enormity of the erosional episode and broad extent of river system that drained the Grenvillian Mountains was first recognized with the advent of detrital zircon geochronology as a tool of provenance analysis. Initially, zircon grains of Grenvillian age were recovered from early Neoproterozoic sedimentary basins located in northwestern Canada, more than 3000km away from the nearest probable sources in the Grenville Province of eastern Laurentia. Paleocurrents derived from cross-bedding in thick fluvial deposits preserved in these basins showed regionally consistent west-northwesterly transport, lending support to the paleogeographic model. Correlative strata, located thousands of kilometers to the south, in the Canadian and US Cordillera, exhibit similar detrital zircon age distributions providing further support for the large-scale river system. These data also indicate that the fluvial system was laterally extensive and likely originated from multiple sources along the great length of the Grenvillian mountain front. Deposits representing the proximal parts of the system have now been recognized in the subsurface of the central US, where they comprise several stratigraphic sequences that can be tied to the various stages of tectonic evolution of the Grenvillian orogeny. The sequences correlate well with outcrop exposures preserved in the Midcontinent Rift system and Great Lakes region to the north. Among these are syn-collisional rift deposits and post-collisional foreland basin deposits displaying features such as axial flow patterns that indicate deposition by trunk rivers flowing parallel to the mountain front. Similar stratigraphic successions are preserved around the North Atlantic in Scotland, Shetland, East Greenland, Svalbard, and Norway. Detrital zircon grains from these successions are dominated by late Paleoproterozoic and late Mesoproterozoic ages inferred to have been derived from source terranes of the Grenville Province in eastern Laurentia. Detrital zircon geochronology indicates that Grenville-age detritus was reworked into numerous Phanerozoic successions around the globe. Some of this detritus was derived directly from uplift and erosion of Grenville Province rocks or recycling of detritus from Grenvillian foreland basin deposits during Appalachian-Hercynian orogenesis and assembly of the Pangea supercontinent. Late Mesoproterozoic detritus has been continually recycled into younger stratigraphic successions and remains a significant component of modern river sediments.
- Detrital zircon geochronology
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)