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 Karl, S.M., Haeussler, P.J., Himmelberg, G.R., Zumsteg, C.L., Layer, P.W., Friedman, R.M., Roeske, S.M.,and Snee, L.W., 2015, Geologic map of Baranof Island: U.S. Geological Survey Scientific Investigations Map SIM-3335, pamphlet 82 p., 1 sheet, scale 1:250,000.
Symbol KJkk
Unit name Khaz Complex of the Kelp Bay Group
Description The Khaz Complex is a name revision herein for the Khaz Formation of Loney and others (1975). The name is revised because the term formation is used for stratigraphic units; rocks of the the Khaz Complex do not retain internal stratigraphy, do not have stratigraphic relations to adjacent units, and are characterized by pervasive ductile to brittle high strain deformation textures. The Khaz Complex is composed dominantly of slatey argillite and tuff that contain blocks of various sedimentary, volcanic, plutonic, and metamorphic lithologies. The argillite, tuff, and graywacke matrix lithologies are locally massive, locally retain turbidite depositional features, and locally contain slump structures and slumped blocks. Chaotic deformation disrupts layering. Tectonic blocks incorporated into the matrix include volcanic and sedimentary rocks from the downgoing oceanic plate, sedimentary and igneous rocks from the accretionary wedge, metamorphic rocks from deeper in the subduction complex, and rocks derived from the upper plate that are mixed by multiple generations of faults. The Khaz Complex correlates with other components of the mélange facies of the upper Mesozoic Chugach accretionary complex of Plafker and others (1976), including parts of the Uyak Complex on Kodiak Island, the McHugh Complex of the Chugach Mountains, and the mélange facies of the Yakutat Group
Lithology Sedimentary

Correlated geologic units

Label KJsx
Description Khaz Complex or melange associated with the Sitka Graywacke, including Freeburn assemblage
Geologic age Jurassic to Early-Cretaceous
Geologic setting Melange
Lithology Form Importance
Melange < Tectonite Melange, matrix Major