Intermediate granitic rocks

Unit symbol: Klgr
Age range Late Cretaceous (83.6 to 72.1 Ma)
Lithology: Igneous - Plutonic
Group name: Intermediate granitic rocks
Granitic rocks including alaskite, granite, quartz monzonite, and dominantly granodiorite of Late Cretaceous age, generally between 85 and 70 Ma. Sparsely distributed in western and south-central Alaska, the largest exposures are the isolated pluton in the Hooper Bay quadrangle and a number of monzogranite to quartz monzodiorite plutons on the Seward Peninsula. Important additional exposures include the so-called tin granites of the Seward Peninsula (Till and others, 2010; 2011). Other areas of significant exposure are in the Talkeetna Mountains north of Anchorage and across the Susitna basin in the Tyonek quadrangle. In the Yukon-Koyukuk Basin (Shungnak, Hughes, and Melozitna quadrangles), large and small plutons of granodiorite and quartz monzonite are spatially associated with the syenitic rocks of unit Ksy, but these rocks are significantly younger than unit Ksy. A small pluton in the Circle quadrangle yields a K/Ar cooling age of 72.8 Ma and is included in this unit; however, given its setting (Wilson and others, 1984), the age may be reset and the pluton may be an older Cretaceous pluton more typical of the Yukon-Tanana Upland. Similarly, other plutons of this unit in the Circle and Big Delta quadrangle yield discordant ages and may also be thermally reset plutons of older Cretaceous age (see, for example, Smith and others, 1994). A number of small, dioritic plutons of Late Cretaceous age also occur in the eastern Taylor Mountains and Lake Clark and Iliamna quadrangles

Source map information

Source map Winkler, G.R., compiler, 1992, Geologic map and summary geochronology of the Anchorage 1° x 3° quadrangle, southern Alaska: U.S. Geological Survey Miscellaneous Investigations Series Map I-2283, scale 1:250,000.
Symbol Kw
Unit name Willow Creek pluton
Description Pervasively altered, zoned pluton; based on its distinctive aeromagnetic signature it is interpreted to extend at least to northern boundary of map area. Pluton has a 30- to 200-m wide outer margin of hornblende quartz diorite and lesser hornblende tonalite. Core is hornblende-biotite granodiorite, and lesser hornblende-biotite quartz monzonite and biotite quartz monzonite. Foliation is common, particularly along margins. Pluton hosts mineralized veins.
Lithology Igneous

Correlated geologic units

Label Kgdt
Description Granodiorite
Geologic age Campanian
Geologic setting Intrusive
Lithology Form Importance
Granodiorite < Granitic < Plutonic < Igneous Pluton Major
Tonalite < Granitic < Plutonic < Igneous Pluton Minor
Quartz-monzonite < Syenitic < Plutonic < Igneous Pluton Minor
Diorite < Dioritic < Plutonic < Igneous Pluton Incidental
Quartz-diorite < Dioritic < Plutonic < Igneous Pluton Incidental
Quartz-monzodiorite < Dioritic < Plutonic < Igneous Pluton Incidental