Granodiorite to quartz monzodiorite

Unit symbol: TKgd
Age range Tertiary, Paleocene, or Late Cretaceous, Maastrichtian (72.1 to 56 Ma)
Lithology: Igneous - Plutonic
Group name: Granitic rocks of southern and interior Alaska
Typically described as granodiorite, quartz diorite, tonalite, monzonite, and quartz monzodiorite, these plutons compositionally overlap with unit TKg, described above, but are the more mafic plutons in this age range. Also widespread, they tend lie at the periphery of the TKg belt of plutons. They are locally weakly foliated and hypidiomorphic-granular or seriate in texture. K/Ar ages on biotite and hornblende range between 73.5 and 60.0 Ma—very slightly older than unit TKg. An outlier to the belt, a fine-grained hornblende granodiorite, is found on Saint Matthew Island and yielded a K/Ar age on hornblende of 62.3±2.0 Ma (Patton and others, 1975)

Source map information

Source map Wilson, F.H., and Hults, Chad, 2006, Unpublished data.
Symbol TKg
Unit name Granitic rocks
Description Fine-, medium-, and coarse-grained, light- to dark-gray, rarely pink plutonic granitic rocks. Chiefly quartz monzonite, granodiorite, and quartz diorite. Subdivision of quartz diorite and diorite from original Hoare and Coonrad (1978) unit.
Lithology Igneous

Correlated geologic units

Label TKqd
Description Quartz diorite and diorite dikes, stocks, and small plutons
Geologic age Maastrichtian to Paleocene
Geologic setting Intrusive
Lithology Form Importance
Diorite < Dioritic < Plutonic < Igneous Pluton Indeterminate, major
Quartz-diorite < Dioritic < Plutonic < Igneous Pluton Indeterminate, major
Quartz-monzodiorite < Dioritic < Plutonic < Igneous Pluton Minor
Granodiorite < Granitic < Plutonic < Igneous Pluton Minor
Gabbroic < Plutonic < Igneous Pluton Incidental
Gabbro < Gabbroic < Plutonic < Igneous Pluton Incidental