Arc Tempos, Tectonic Styles, and Sedimentation Patterns During Evolution of the North American Cordillera: Constraints From the Retroarc Detrital Zircon Archive
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The North American Cordillera orogenic system experienced interrelated cycles of magmatic arc lulls and flare-ups with associated shifts in isotopic signatures, varying extensional to contractional deformation, and changing basin sedimentation patterns during protracted (>100 Myr) subduction and terrane accretion. Here we evaluate the retroarc sedimentary archive of arc magmatism using integrated U-Pb geochronologic and Hf isotopic analysis of arc-derived zircon grains from Triassic to Cretaceous foreland basin strata spanning southern Nevada to Montana. Zircon U-Pb age data record early arc magmatism from ca. 260–210 Ma with a Late Triassic flare-up, a 205–180 Ma lull, a 175–145 Ma Jurassic flare-up, a 140–125 Ma lull, and a 120–85 Ma Cretaceous flare-up, consistent with pluton age patterns in the arc. Triassic age zircon grains have a wide range of ε values that reflect varying depleted mantle to evolved crustal components during early arc growth. Jurassic-age grains have overall evolved ε in the southern Nevada and Utah regions, to mostly juvenile values in the Montana region, consistent with a Jurassic arc system built on variably evolved to more juvenile crust going northward. Zircon ε values show a distinct pulldown from 120–85 Ma, with median ε decreasing from about +10 to -10, consistent with isotopic shifts in the Sierra Nevada and Idaho plutonic complexes that migrated inboard and interacted with thickened continental crust. A compilation of zircon data from forearc strata shows broadly similar age and isotopic patterns, although the 140–125 Ma lull is better recorded and the Cretaceous flare-up less well recorded compared to the retroarc. The Jurassic and Cretaceous flare-ups and associated shifts in isotopic signatures occurred during episodes of increasing plate convergence rates and terrane accretion, decreasing dip of subducting slabs, intraplate shortening, and enhanced foreland subsidence. Paleo-tectonic reconstructions highlight spatial and temporal interconnections among arc tempo, deformation styles, and sedimentation in forearc and retroarc basins, linked to both subduction dynamics and feedbacks among crustal thickening, migration of arcs into more fertile host crust, formation and removal of eclogitic arc roots, and magmatic flare-ups within the orogenic system. Hf Hf Hf Hf
Arc tempo; Cordilleran cycle; Detrital zircon; Foreland basin; Hf isotope; U-Pb geochronology
Tectonics and Structure
Arc Tempos, Tectonic Styles, and Sedimentation Patterns During Evolution of the North American Cordillera: Constraints From the Retroarc Detrital Zircon Archive.
Earth-Science Reviews, 216