Kakhonak Complex and Tlikakila complex of Carlson and Wallace (1983)

Unit symbol: JPk
Age range Jurassic, Triassic, and older? (259.9 to 145 Ma)
Lithology: Metamorphic
Group name: Kakhonak Complex and Tlikakila complex of Carlson and Wallace (1983)
Kakhonak Complex is a lithologically diverse and complex assemblages of metamorphosed mafic plutonic, volcanic, and sedimentary rocks found on west side of Cook Inlet, defined by Detterman and Reed (1980), associated with the Alaska-Aleutian Range batholith and similar rocks in the Talkeetna Mountains. Detterman and Hartsock (1966) mapped metalimestone, argillite, quartzite, metatuff, greenstone, and phyllite as undivided metamorphic rocks in the Kenai and Iliamna quadrangles. Detterman and Reed (1980) named these rocks the Kakhonak Complex and described unit that largely consists of roof pendants within the Alaska-Aleutian Range batholith and along the eastern margin of the Jurassic part of the batholith. They thought that the Kakhonak Complex represented, in part, the metamorphic equivalent of Upper Triassic Kamishak and Lower Jurassic Talkeetna Formations, which are in the vicinity. However, quartzite and quartz-mica schist within the Kakhonak Complex have no direct equivalent within the sedimentary rocks of the area, which indicates that other protoliths may have contributed to the complex. Because Permian rocks were known from Puale Bay, south of the map area, a possible Paleozoic age was not ruled out by Detterman and Reed (1980); subsequent analysis of Alaska Peninsula drill cores has conclusively demonstrated the presence of Paleozoic rocks on the peninsula (R.B. Blodgett, written commun., 2011). Internal contacts are typically faults, resulting in a tectonic mix of lithologies. Although most of the rocks of this complex are greenschist facies, the rocks range in metamorphic grade from not metamorphosed to granulite facies. Intrusive rocks provide a minimum age for the Kakhonak Complex. On the west side of the batholith, the lithologically similar Tlikakila complex of Carlson and Wallace (1983; see also Wallace and others, 1989; Amato and others, 2007) straddles Lake Clark and the Lake Clark Fault without apparent offset. Nelson and others (1983) mapped a unit somewhat more extensive than the Tlikakila complex as shown by Wallace and others (1989) or Amato and others (2007); Nelson and others (1983) described “a diverse complex of metamorphosed and highly deformed rocks, whose protoliths include calcareous to siliceous clastic rocks, limestone, thin-bedded chert, massive basalt, massive to layered gabbro and pyroxenite, and ultramafic rocks. Most of complex metamorphosed to greenschist facies but ranges from nonmetamorphosed to amphibolite facies” (Nelson and others, 1983). 40Ar/39Ar ages on mica from metasedimentary rocks range between 192 and 176 Ma (Amato and others, 2007) provide a minimum age for metamorphism, which is somewhat older than K/Ar and U/Pb ages determined on nearby parts of the Jurassic phase of the Alaska-Aleutian Range batholith (unit Jgr, 172 to 160 Ma). Detrital zircon data from a single sample of chert-pebble conglomerate (Amato and others, 2007) potentially indicates a Paleozoic source terrane for the conglomerate. The age distribution of the zircons is similar to that for the Terra Cotta Mountains Sandstone (D.C. Bradley, oral commun., 2012; unit Stc here). Unit also includes migmatitic border rocks of the Jurassic plutons and undifferentiated metamorphic and plutonic rocks in the Talkeetna Mountains quadrangle (units Jpmu and Jgdm of Csejtey and others, 1978)

Source map information

Source map Schmidt, J.M., 2007, Unpublished data.
Symbol Jpmu
Unit name Plutonic and metamorphic rocks, undifferentiated
Description Intermixed mosaic of most of the previously discussed Jurassic metamorphic and plutonic rocks (Jtr, Jgd, Jgdm, Jqd, Jgs, and Jps). Two rock types, amphibolite and sheared quartz diorite, dominate the terrane.
Lithology Metamorphic

Correlated geologic units

Label Jpmu
Description Metamorphic and plutonic rocks, undifferentiated, Jurassic,
Geologic age Early-Jurassic to Middle-Jurassic
Geologic setting Metamorphic, undivided
Lithology Form Importance
Metamorphic Indeterminate, major