Khaz Complex

Unit symbol: Kkbm
Age range Cretaceous and older (163.5 to 89.8 Ma)
Lithology: Tectonite
Group name: Kelp Bay Group, undivided
Formerly mapped as the Khaz Formation of the Kelp Bay Group, Karl and others (2015) renamed it the Khaz Complex, which reflects that the unit is a mélange and does not have an internal stratigraphy, nor clear stratigraphic relation to surrounding unit. The Khaz Complex includes chaotically deformed rocks composed of blocks of greenstone, greenschist, tuff, graywacke, argillite, chert, limestone, and phyllite in a foliated argillaceous and tuffaceous matrix (Johnson and Karl, 1985). Unit is dominantly slaty argillite and tuff enclosing blocks of varying lithology, where the blocks and matrix are disrupted and displaced along thrust, strike-slip, and extensional-slip faults (Karl and others, 2015). As shown here, unit also includes the Freeburn assemblage of Johnson and Karl (1985), a collage composed of kilometer-scale, fault-bounded, lozenge-shaped blocks of metasedimentary and metavolcanic rocks, which form a continuous belt on Chichagof and Yakobi Islands immediately west of the Border Ranges Fault. The dominant lithologies include tuffaceous argillite, tuff, massive greenstone, and graywacke turbidite. Other common lithologies include chert, limestone, and phyllite. Age of formation of the mélange is not well controlled; Brew and others (1988) reported late Tithonian (Late Jurassic) Buchia fischherina from argillite matrix, and Valanginian to Hauterivian radiolarians were reported from float near Sitka. Limestone blocks in the mélange contain poorly preserved scleractinian corals, and sandstone blocks contain Buchia piochii(?) of Tithonian age and Buchia subokensis and Buchia okensis of Berriasian (earliest Cretaceous) age (Karl and others, 2015). Potassium-argon ages of 98 to 95 Ma (Decker and others, 1980), on sericite concentrated from phyllite, yielded an apparent metamorphic age for the Khaz Complex of early Late Cretaceous

Source map information

Source map Johnson, B.R., and Karl, S.M., 1985, Geologic map of western Chichagof and Yakobi Islands, southeastern Alaska: U.S. Geological Survey Miscellaneous Investigations Series Map I-1506, pamphlet, 15 p., 1 sheet, scale 1:125,000.
Symbol Kfl
Unit name Limestone within Freeburn assemblage
Description Limestone blocks within the Freeburn assemblage. Protolith age for limestone is probably Triassic, based on Triassic age of adjacent (Whitestripe) limestone unit. Emplacement age is the age of the Freeburn Assemblage, a tectonic unit that formed in the Cretaceous.
Lithology Sedimentary

Correlated geologic units

Label KJkl
Description Khaz melange and related units, limestone blocks, southeast Alaska, including limestone blocks in Freeburn Assemblage
Geologic age Permian to Triassic
Geologic setting Melange
Lithology Form Importance
Marble < Metacarbonate < Metasedimentary < Metamorphic Major