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TitleEvolution of the Late Cretaceous Nanaimo Basin, British Columbia, Canada: definitive provenance links to northern latitudes
AuthorMahoney, J B; Haggart, J W; Grove, M; Kimbrough, D L; Isava, V; Link, P K; Pecha, M E; Fanning, C M
SourceGeosphere vol. 17, no. 6, 2021 p. 2197-2233, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20200721
PublisherGeological Society of America
Mediapaper; digital; on-line
File formatpdf; html
ProvinceBritish Columbia
NTS92B/05; 92B/06; 92B/11; 92B/12; 92B/13; 92B/14; 92C/09; 92C/10; 92C/15; 92C/16; 92F/01; 92F/02; 92F/07; 92F/08; 92F/09; 92F/10; 92F/15; 92F/16; 92G
Subjectstectonics; geochronology; sedimentology; stratigraphy; paleontology; geochemistry; Science and Technology; Nature and Environment; Upper Cretaceous; basin evolution; paleogeography; tectonic evolution; orogenies; terranes; subsidence; magmatism; radiometric dating; uranium lead dating; detrital minerals; zircon dates; argon argon dating; isotopic studies; clasts; provenance; sediment dispersal; depositional history; models; nomenclature; stratigraphic analyses; biostratigraphy; lithostratigraphy; Nanaimo Basin; Canadian Cordillera; Coast Mountains Batholith; Belt Supergroup; Idaho Batholith; Atlanta Lobe; Lemhi Subbasin; Mesoproterozoic; Wrangellia; Coast Plutonic Complex; Laurentia; Yakutat Group; Pelona-Orocopia- Rand Schists; Phanerozoic; Mesozoic; Cretaceous; Precambrian; Proterozoic
Illustrationsgeoscientific sketch maps; schematic cross-sections; stratigraphic sections; block diagrams; tables; plots; time series; bar graphs; photographs; geochronological charts
ProgramGSC Pacific Division
Released2021 11 08
AbstractAccurate reconstruction of the Late Cretaceous paleogeography and tectonic evolution of the western North American Cordilleran margin is required to resolve the long-standing debate over proposed large-scale, orogen-parallel terrane translation. The Nanaimo Basin (British Columbia, Canada) contains a high-fidelity record of orogenic exhumation and basin subsidence in the southwestern Canadian Cordillera that constrains the tectonic evolution of the region. Integration of detrital zircon U-Pb geochronology, conglomerate clast U-Pb geochronology, detrital muscovite 40Ar/39Ar thermochronology, and Lu-Hf isotopic analysis of detrital zircon defines a multidisciplinary provenance signature that provides a definitive linkage with sediment source regions north of the Sierra Nevada arc system (western United States).
Analysis of spatial and temporal provenance variations within Nanaimo Group strata documents a bimodal sediment supply with a local source derived from the adjacent magmatic arc in the southern Coast Mountains batholith and an extra-regional source from the Mesoproterozoic Belt Supergroup and the Late Cretaceous Atlanta lobe of the Idaho batholith. Particularly robust linkages include: (1) juvenile (epsilon-Hf > +10) Late Cretaceous zircon derived from the southern Coast Mountains batholith; (2) a bimodal Proterozoic detrital zircon signature consistent with derivation from Belt Supergroup (1700-1720 Ma) and ca. 1380 Ma plutonic rocks intruding the Lemhi subbasin of central Idaho (northwestern United States); (3) quartzite clasts that are statistical matches for Mesoproterozoic and Cambrian strata in Montana and Idaho (northwestern United States) and southern British Columbia; and (4) syndepositional evolved (epsilon-Hf > -10) Late Cretaceous zircon and muscovite derived from the Atlanta lobe of the Idaho batholith. These provenance constraints support a tectonic restoration of the Nanaimo Basin, the southern Coast Mountains batholith, and Wrangellia to a position outboard of the Idaho batholith in Late Cretaceous time, consistent with proposed minimal- fault- offset models (< ~1000 km).
Summary(Plain Language Summary, not published)
The coastal region of western Canada is geologically complex, characterized by extensive faulting and translocation movements that have taken place over the past 200 million years of Earth history. These movements of geological regions, or terranes, have resulted from the processes of plate tectonics, or the actions that drive the tectonic plates forming the Earth's outer crust. Many of the rocks of Vancouver Island, British Columbia, are hypothesized to have formed at low, tropical latitudes about 200 million years ago, as evidenced by tropical-type fossil organisms that are found within them, and were then transported northward on the tectonic plates. But just when these rocks moved from their equatorial origin to their modern-day high temperate location is a matter of geological debate: some geologists believe that these rocks must have moved north by about 170 million years ago, while others postulate that this movement took place as recently as 65 million years ago. The authors of this contribution have utilized a variety of geochemical techniques to determine that the source of the sediments in rocks about 80 million years of age found along the southeastern region of Vancouver Island can be tied closely to unique geological sources in Idaho and northwest Montana, thus establishing that these Vancouver Island rocks were at their present latitudinal position by at least 80 million years ago. Ancient river systems of that time transported the sediments from their source in Idaho and Montana to the southern Vancouver Island region.

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