Late Devonian magmatism and clastic deposition in the upper Earn Group (central Yukon, Canada) mark the transition from passive to active margin along western Laurentia

The Earn Group of central Yukon records the transition from a passive to an active margin along western Laurentia in Late Devonian. Fine-grained clastic rocks and chert lower contain late Early Middle Devonian fossils were deposited offshelf environment. upper comprises mixture sandstone conglomerate, fine-grained siliciclastic rocks, widespread crystal lithic tuff. Zircons this succession are precisely dated using chemical abrasion isotope dilution thermal ionization mass spectrometry (CA–ID–TIMS) methods on igneous (ca. 363 Ma) detrital 378–363 grains ages confirmed by Frasnian Famennian fossils. Abrupt, along-strike facies changes within Glenlyon–Tay River area occur across mapped faults that inferred have originated as syndepositional extension Occurrences ca. Ma tuff horizons all provide temporal correlation area. Diorite plutons intrude Paleozoic U–Pb zircon crystallization dates 364 Ma. diorite has calc-alkaline composition consistent with arc magmatism or crustal contamination. is coincident onset allochthonous Yukon–Tanana terrane, related rifting opening Slide Mountain ocean back-arc setting. Magmatic thus represent part remnant continental stranded behind Mississippian.