Recalibrating Rodinian rifting in the northwestern United States

Abstract

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.

How old are the Jack Hills metasediments really?: The case for contamination of bedrock by zircon grains in transported regolith

“…This comparison of reference zircon data in inverse Concordia space did not reveal any discernible systematic trends to indicate the presence of additional surface-derived common lead associated with the fast pulse protocol (Brennan et al, 2021), giving confidence that the method is well suited to characterizing the age distribution of a large sample pool. Statistically, the fast ablation sample data were somewhat more scattered, but with no change to the indicated amount of discordance (Brennan et al, 2021).…”

“…Because the fast pulse protocol utilised here does not include pre-ablation cleaning pulses to remove possible surface contamination, an assessment was undertaken previously by Brennan et al (2021), comparing the Pb isotope data from fast pulse analyses to a corresponding 'conventional' LA-ICP-MS data set collected on the same grains, reference materials and instrumentation. This comparison of reference zircon data in inverse Concordia space did not reveal any discernible systematic trends to indicate the presence of additional surface-derived common lead associated with the fast pulse protocol (Brennan et al, 2021), giving confidence that the method is well suited to characterizing the age distribution of a large sample pool. Statistically, the fast ablation sample data were somewhat more scattered, but with no change to the indicated amount of discordance (Brennan et al, 2021).…”

Supplemental Material: Neoproterozoic to early Paleozoic tectono-stratigraphic framework for central Idaho: Windermere Supergroup in the northern sector of the U.S. Cordillera

“…Detrital zircon studies of Neoproterozoic-Cambrian strata in northeastern Washington (Linde et al, 2017;Box et al, 2020;Brennan et al, 2021a) have established a general provenance framework. The ca.…”

“…For example, in the conterminous U.S. sector of the Laurentian margin, prior workers have described at least three punctuated phases of protracted rifting: (1) ca. 780-740 Ma (e.g., Dehler et al, 2017;Brennan et al, 2021a), (2) ca. 670-600 Ma, and (3) younger than ca.…”

A tectonic model for the Transcontinental Arch: Progressive migration of a Laurentian drainage divide during the Neoproterozoic–Cambrian Sauk Transgression

“…780 Ma Gunbarrel magmatic event (Harlan et al., 2003). Related localized sedimentation occurred shortly after (Brennan et al., 2021; Dehler et al., 2017; Lund et al., 2003; Karlstrom et al, 2000) and along most of the western margin by ca. 720 Ma (e.g.…”