Alaska Range melange

Unit symbol: Kmar
Age range Cretaceous (145 to 66 Ma)
Lithology: Tectonite
Group name: Mélanges
Fault-bounded tectonic and probably sedimentary mélange (olistostrome) of Paleozoic and upper Mesozoic rocks that consist of three distinct, intensely deformed, sheared, and intermixed rock suites (Csejtey and others, 1992). Suite one consists of “medium- to thin-bedded, greenish-gray to tan-colored, locally black, cherty tuff, chert, argillite, and fine-grained volcanic sandstone” that commonly shows slightly graded bedding (Csejtey and others, 1992). It contains “Radiolaria, and conodont fragments in cherty tuffs and associated rocks range in age from Late(?) Devonian to Mississippian” (Csejtey and others, 1992, p. 29). Suite two consists of “dark-gray to black, flysch-like rocks of argillite, slate, shale, fine- to medium-grained graywacke, subordinate bedded chert, and both chert-pebble and polymictic conglomerate” (Csejtey and others, 1992, p. 29) that is lithologically identical to flysch of unit Kfy. In the Mount Hayes quadrangle, minor andesite and dacite are associated with the flysch-like assemblage (Nokleberg and others, 1992a). Suite three is “lenses and elongate blocks of medium-gray, generally medium-bedded and rarely massive, fine- to medium-grained fossiliferous limestone” that contains megafossils and conodonts of Silurian to Middle Devonian age (Csejtey and others, 1992). North of the Denali Fault System, (Csejtey and others, 1992) report that the mélange contains a “poorly exposed small sliver of serpentinized ultramafic rocks, altered basalt, green and maroon tuff, and recrystallized chert, all of unknown age.” In general, the mélange is spatially associated with the Denali Fault System; however, a large area of the exposure extends along the west side of Broad Pass, trending away from the fault system

Source map information

Source map Csejtey, Bela, Jr., Nelson, W.H., Jones, D.L., Silberling, N.J., Dean, R.M., Morris, M.S., Lanphere, M.A., Smith, J.G., and Silberman, M.L., 1978, Reconnaissance geologic map and geochronology, Talkeetna Mountains quadrangle, northern part of Anchorage quadrangle, and southwest corner Healy quadrangle, Alaska: U.S. Geological Survey Open-File Report 78-558-A, 60 p., 1 sheet, scale 1:250,000.
Symbol DSga
Unit name Graywacke, argillite, and shale
Description This unit is poorly known. The component rocks identified are medium to dark gray, sheared and tightly folded with vertical dips, and occur intercalated in beds as much as 1 m thick.
Lithology Sedimentary

Correlated geologic units

Label Kmar
Description Melange south of McKinley Fault
Geologic age Silurian to Cretaceous
Geologic setting Melange
Lithology Form Importance
Melange < Tectonite Melange, matrix Major