Saint Elias suite of Gordey and Makepeace (2003) and similar rocks

Unit symbol: KJse
Age range Early Cretaceous and Late Jurassic (163.5 to 132.9 Ma)
Lithology: Igneous - Plutonic
Group name: Saint Elias suite of Gordey and Makepeace (2003) and similar rocks
Chiefly quartz monzodiorite, but compositionally diverse: ranges from granite to diorite. Generally foliated and locally gneissic, especially in plutons enclosed in the Strelna Metamorphics of Plafker and others (1989) (included in unit PIPsm, here). Also includes rocks locally known as the Chitina Valley batholith composed mainly of diorite, leucodiorite, and tonalite, but includes gabbro, especially near contacts (Winkler and others, 1981). Generally medium-grained but varies from fine- to coarse-grained and pegmatitic. Ranges from weakly foliated to nonfoliated in interior of plutons to strongly foliated and locally mylonitic near contacts. K/Ar and 40Ar/39Ar dates indicate plutonic ages as old as 162 Ma (Brew and others, 2013) and possibly as young as 117 Ma (Dodds and Campbell, 1988); metamorphic ages are as young as 52 Ma (Roeske and others, 2003). Unit includes the metaplutonic rocks of metamorphic complex of Gulkana River of Nokleberg (USGS, written commun., 1997) as well as isolated fine- to medium-grained, hypidiomorphic granular textured granitic and minor monzonite and diorite dikes, stocks, and small plutons that are largely undated. A single K/Ar hornblende date of 129 Ma (Nokleberg and others, 1992b) suggests at least part of the metamorphic complex is Early Cretaceous in age. These central Alaska exposures are locally metamorphosed to lower greenschist facies. A southern extension of this unit of similar quartz diorite and tonalite plutons is in the Mount Fairweather, Sitka, and Juneau quadrangles as the suite extends through the Yukon and British Columbia of Canada (Gordey and Makepeace, 2003; Massey and others, 2005). On Chichagof Island, these plutons are spatially associated with others that have yielded Middle Jurassic ages; the diorite and tonalite plutons of unit KJse may also form sills and dikes within the Whitestripe Marble and along the contacts of the Whitestripe Marble and Goon Dip Greenstone (Johnson and Karl, 1985) along both sides of the Peril Strait Fault. Where mapped in the Mount Fairweather quadrangle, unit also includes Jurassic trondhjemite (Roeske and others, 1992) that has not been distinguished as a separate unit; it is the same age as the trondhjemite of the Talkeetna Mountains and northern Alaska Peninsula (unit Jtr) and may have originated from the same magmatic system. While the older country rocks of these two units bear some similarities, the voluminous Jurassic sedimentary section and Talkeetna magmatic arc products (which are spatially associated with the trondhjemite) are not associated with the Saint Elias Suite or Chitina Valley batholith

Source map information

Source map Winkler, G.R., Silberman, M.L., Grantz, Arthur, Miller, R.J., and MacKevett, E.M., Jr., 1981, Geologic map and summary geochronology of the Valdez quadrangle, southern Alaska: U.S. Geological Survey Open-File Report 80-892-A, 2 sheets, scale 1:250,000. and modifications by Winkler, 1997).
Symbol Jc
Unit name Chitina Valley batholith
Description Weakly to strongly foliated compositionally diverse plutonic rocks. Dominant lithology is fine-to medium-grained hypidiomorphic granular quartz monzodiorite, but quartz diorite, tonalite, and granodiorite are nearly as abundant.
Lithology Igneous

Correlated geologic units

Label KJse
Description Saint Elias Suite, biotite hornblende granodiorite; lesser tonalite; locally quartz monzodiorite, quartz diorite, granite, and quartz monzonite
Geologic age Middle-Jurassic to Valanginian
Geologic setting Intrusive
Lithology Form Importance
Granodiorite < Granitic < Plutonic < Igneous Pluton Major
Quartz-diorite < Dioritic < Plutonic < Igneous Pluton Minor
Tonalite < Granitic < Plutonic < Igneous Pluton Minor