Mélange facies

Unit symbol: KJm
Age range Cretaceous or Jurassic? (201.3 to 100.5 Ma)
Lithology: Tectonite
Group name: West-central Alaska mélange (Angayucham)
Tectonic assemblage of blocks of carbonate rocks, chert, metagraywacke, and altered mafic extrusive and intrusive rocks in a matrix of phyllite exposed in low hills surrounding the Yukon-Koyukuk Basin. The mélange locally varies in metamorphic grade from pumpellyite to greenschist facies (Patton and others, 2009; Till and others, 2008a). Till and others (2008a) report a block of mafic schist on the Baird Mountains and Ambler River quadrangle boundary that contains abundant blue amphibole, probably crossite. Age of the mélange is not well controlled; Till and others (2008a) report Mississippian radiolarians from metachert and metalimestone bodies yielding Middle and Late Devonian and Ordovician conodonts (Pallister and Carlson, 1988, cited in Till and others, 2008a). Patton and others (2009) suggested that the mélange probably formed during time of tectonic emplacement of Angayucham-Tozitna terrane structurally above the Arctic Alaska and Ruby terranes during the Early Cretaceous. Includes unit KJm of Patton and others (2009), but does not include that part of unit KJm of Karl and others (1989a) in the northwest part of the Baird Mountains quadrangle, which has been assigned here to the Okpikruak Formation (unit Kofm). The outcrop pattern of this part of unit KJm of Karl and others (1989a) projects into the adjoining Noatak quadrangle where, it was mapped as Okpikruak Formation at the top of the Kelly River allochthon by C.G. Mull and H.S. Sonneman (Exxon, unpub. report, 1968–1974)

Source map information

Source map Karl, S.M., Dumoulin, J.A., Ellersieck, Inyo, Harris, A.G., and Schmidt, J.M., 1989, Preliminary geologic map of the Baird Mountains and part of the Selawik quadrangles, Alaska: U.S. Geological Survey Open-File Report 89-551, 65 p., 1 sheet, scale 1:250,000.
Symbol MzPzm
Unit name Melange and phyllite
Description Dark gray to black siliceous phyllite with fault-bounded blocks of marble, ribbon chert, dolostone, metabasite, schist, and serpentinite.
Lithology Sedimentary

Correlated geologic units

Label MzPzl
Description Melange between Angayucham-Tozitna and Arctic Alaska and Ruby terranes
Geologic age Jurassic to Early-Cretaceous
Geologic setting Melange
Lithology Form Importance
Melange < Tectonite Melange, blocks Major