Foliated granitic rocks of Southeast Alaska

Unit symbol: Ksfg
Age range middle Cretaceous? (145 to 89.8 Ma)
Lithology: Igneous - Plutonic
Group name: Foliated granitic rocks of southeast Alaska
Medium-grained, very light-gray to gray biotite-hornblende granodiorite that has local quartz diorite, quartz monzodiorite, tonalite, and granite phases. Foliation, defined by the alignment of mafic minerals, is usually present. This unit consists of plutonic bodies within the Skagway and Mount Fairweather quadrangles and a large area of foliated quartz monzonite and granodiorite in the Ketchikan quadrangle associated with the Coast Plutonic Complex of Brew and Morrell (1979b). Foliations generally parallel those in the host rocks except for local divergences near contacts. Contact aureoles in the host rocks are generally narrow zones of hornfels (D.A. Brew, written commun., 2002). Age control is generally lacking, but nonfoliated plutons of similar composition in the vicinity yield cooling ages of about 120 to 110 Ma. The rocks in the Ketchikan quadrangle yield Eocene K/Ar ages and a U/Pb lower intercept age of 107 Ma (Rubin and Saleeby, 2000). An unpublished U/Pb TIMS multigrain zircon age was much older, ~177 Ma (S.M. Karl, unpub. data); the sample, collected near Haines, displays some evidence of inheritance, yet may indicate inclusion of Jurassic plutonic rocks in this unit

Source map information

Source map Gilbert, W.G., 1988, Preliminary geology and geochemistry of the north Chilkat Range: Alaska Division of Geological and Geophysical Surveys Report of Investigations 88-8, 2 sheets, scale 1:36,200.
Symbol Kgdf
Unit name Foliated granodiorite
Description Weakly to strongly foliated, fine- to coarse-grained biotite-hornblende granodiorite. Subordinate granite, quartz monzodiorite, quartz diorite. Color index 10-30, biotite mostly less than hornblende in abundance. Equigranular, locally seriate. Locally abundant diabase xenoliths.
Lithology Igneous

Correlated geologic units

Label Kgdf
Description Foliated granodiorite
Geologic age Aptian to Albian
Geologic setting Intrusive
Lithology Form Importance
Granodiorite < Granitic < Plutonic < Igneous Pluton Major