Upper Triassic Karmutsen Formation of Western Canada and Alaska: A Plume-Generated Oceanic Plateau Formed Along a Mid-Ocean Ridge Nucleated on a Late Paleozoic Active Margin

Linking the Wrangellia flood basalts to the Galápagos hotspot

“…The terrane is characterized by similar sequences of Triassic rocks. These rocks, dominated by thick, massive Middle to Upper Triassic tholeiitic flows and pillow lava (i.e., Nikolai Greenstone and Karmutsen Formation), overlie Devonian through Permian volcanic, volcaniclastic, siliciclastic, and carbonate rocks 1 , 10 – 13 . The volcanic rocks are thought to be derived from a “plume-type Pacific mantle source” that was similar to the Ongtong Java or Caribbean oceanic plateaux and may have contributed to the Carnian mass extinction 14 – 19 .…”

“…The flood basalts of Wrangellia (Nikolai and Karmutsen lavas) are variably altered but most are tholeiitic with a minor amount of mildly alkalic flows 13 , 15 – 18 . The Mg# of the basalts ranges from ~ 72 to ~ 27 indicating some rocks are compositionally primitive or near primitive (Mg# = 72–65) whereas others are differentiated (Mg# < 65).…”

“…Thus, the circumstances that led to the accretion of Wrangellia to North America and not the associated island chain requires an explanation. One such explanation could be that Wrangellia was built upon an older, relatively buoyant substrate (e.g., arc basement), whereas the island track was built directly upon oceanic crust 13 . Regardless, if the island chain subducted then the verification of its existence is problematic.…”

Linking the Wrangellia Flood Basalts to the Galápagos Hotspot

“…The flood basalts of Wrangellia (Nikolai and Karmutsen lavas) are variably altered but most are tholeiitic with a minor amount of mildly alkalic flows 13,[15][16][17][18] . The Mg# of the basalts ranges from ~72 to ~27 indicating some rocks are compositionally primitive or near primitive (Mg# = 72-65) whereas others are differentiated (Mg# < 65).…”