U. S. Geological survey pamphlet introduction, tectonic definitions, acknowledgments



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Middle (Narvak) thrust panelÑChiefly structurally interleaved diabase, pillow basalt, tuff, chert, graywacke, argillite, minor limestone, and volcanogenic sandstone, conglomerate, and tuff. Locally abundant gabbro and diabase. Cherts range in age from Late Devonian to Early Jurassic. Limestones mainly Carboniferous. Devonian corals, brachiopods, and graptolites from shale and limestone beds in extreme eastern Alaska. Major accumulations of late Carboniferous and Late Triassic basaltic volcanism; however, many volcanic sequences are not yet well dated. Basalts interpreted as oceanic island or plateau basalt based on associated sedimentary facies and trace-element discriminant patterns. Includes Tozitna, Innoko, and Woodchopper Canyon terranes of Jones and others (1981, 1987) and Grantz and others (1991), and Rampart Group of east-central Alaska.

Narvak thrust panel structurally and stratigraphically complex; generally highly faulted and locally folded. Metamorphosed to greenschist facies and locally blueschist facies, as indicated by glaucophane, at base of thrust panel. Narvak thrust panel structurally overlies Coldfoot terrane to north and Ruby terrane to south; structurally overlain by Koyukuk terrane, and locally in southwestern Alaska, protolith forms stratigraphic basement to Koyukuk terrane. Narvak thrust panel depositionally overlain by Cretaceous clastic deposits of Yukon-Koyukuk Basin, and by Late Cretaceous and early Tertiary Yukon-Kanuti and Kuskokwim Mountains igneous belts. Narvak thrust panel interpreted as a subduction zone complex composed chiefly of oceanic crust and seamounts. Locally in southwestern Alaska, Narvak thrust panel may be stratigraphically overlain by rocks of Koyukuk terrane. REFERENCES: BrosgŽ and others, 1969; Murchey and Harris, 1985; Barker and others, 1988; Jones and others, 1988; Pallister and Carlson, 1988; Pallister and others, 1989; Patton and others, 1977, 1989, 1992; Patton, 1992a, b.





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