Recalibrating Rodinian rifting in the northwestern United States

A lack of precise age constraints for Neoproterozoic strata in the northwestern United States (Washington State), including the Buffalo Hump Formation (BHF), has resulted in conflicting interpretations of Rodinia amalgamation and breakup processes. Previous detrital zircon (DZ) studies identified a...

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Bibliographic Details
Published in:Geology (Boulder) 2021-02, Vol.49 (6), p.617-622
Main Authors: Brennan, Daniel T, Li, Zheng-Xiang, Rankenburg, Kai, Evans, Noreen J, Link, Paul K, Nordsvan, Adam R, Kirkland, Christopher L, Mahoney, J. Brian, Johnson, Tim, McDonald, Bradley J
Format: Article
Language:English
Subjects:
Ablation
absolute age
Age
Amalgamation
Breakup
Buffalo Hump Formation
Crystallization
Deposition
Geochronology
Geochronometry
Geology
Geophysics
Identification
Isotopes
Laser ablation
Lasers
Laurentia
Lead
lithostratigraphy
Lu/Hf
Neoproterozoic
nesosilicates
orthosilicates
plate tectonics
Precambrian
Proterozoic
Radiometric dating
Rifting
Rodinia
Sedimentary rocks
silicates
solid Earth (tectonophysics)
Stevens County Washington
U/Pb
United States
upper Precambrian
Washington
Zircon
zircon group
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Summary:A lack of precise age constraints for Neoproterozoic strata in the northwestern United States (Washington State), including the Buffalo Hump Formation (BHF), has resulted in conflicting interpretations of Rodinia amalgamation and breakup processes. Previous detrital zircon (DZ) studies identified a youngest ca. 1.1 Ga DZ age population in the BHF, interpreted to reflect mostly first-cycle sourcing of unidentified but proximal magmatic rocks intruded during the amalgamation of Rodinia at ca. 1.0 Ga. Alternatively, the ca. 1.1 Ga DZ population has been suggested to represent a distal source with deposition occurring during the early phases of Rodinia rifting, more than 250 m.y. after zircon crystallization. We combined conventional laser-ablation split-stream analyses of U-Pb/Lu-Hf isotopes in zircon with a method of rapid (8 s per spot) U-Pb analysis to evaluate these opposing models. Our study of ∼2000 DZ grains from the BHF identified for the first time a minor (∼1%) yet significant ca. 760 Ma population, which constrains the maximum depositional age. This new geochronology implies that the BHF records early rift deposition during the breakup of Rodinia and correlates with sedimentary rocks found in other late Tonian basins of southwestern Laurentia.
ISSN:0091-7613
1943-2682
DOI:10.1130/G48435.1