Geologic Map of Alaska: Syenitic rocks

Syenitic rocks

Unit symbol:	Ksy
Age range	Cretaceous, Coniacian to Albian (113 to 86.3 Ma)
Lithology:	Igneous - Plutonic
Group name:	Granitic rocks of central and southeast Alaska

Nepheline syenite, syenite, monzonite, and subordinate alkaline plutonic rocks and dikes including malignite, ijolite, shonkinite, and pyroxenite (Patton and Miller, 1968). Part of the “western Yukon-Koyukuk plutonic suite” of Miller (1989), a potassic and ultrapotassic belt that outcrops from the northeast corner of the Bettles quadrangle to Saint Lawrence Island. K/Ar and 40Ar/39Ar ages range from about 95 to 113 Ma with the majority of ages between 105 and 109 Ma

Source map information

Source map	Patton, W.W., Jr., Wilson, F.H., Labay, K.A., and Shew, Nora, 2009, Geologic map of the Yukon-Koyukuk basin, Alaska: U.S. Geological Survey Scientific Investigations Map SIM-2909, 26 p., 2 sheets, scale 1:500,000.
Symbol	Ksy
Unit name	Syenite, monzonite, and nepheline syenite
Description	Composed of syenite, monzonite, and subordinate quartz monzonite, monzodiorite, quartz syenite, and nepheline syenite and related mafic alkaline rocks including malignite, ijolite, shonkinite, and pyroxenite. Unit occurs in two separate Early Cretaceous plutonic belts (fig. 3, sheet 2): a western belt that can be traced from Shungnak quadrangle westward through Selawik quadrangle and southward into the Candle quadrangle and an eastern belt that extends from the northeastern part of Bettles quadrangle to southwestern part of the Nulato quadrangle. Unit is widespread in the western belt, but is confined to a single composite pluton at the northeastern end of the eastern belt
Lithology	Igneous

Correlated geologic units

Label	Ksy
Description	Syenite
Geologic age	Albian to Santonian
Geologic setting	Intrusive

Lithology	Form	Importance
Monzonite < Syenitic < Plutonic < Igneous	Pluton	Major
Syenite < Syenitic < Plutonic < Igneous	Pluton	Major