Quartz monzodiorite

Unit symbol: KJg
Age range Cretaceous to Jurassic (163.5 to 100.5 Ma)
Lithology: Igneous - Plutonic
Group name: Plutonic rocks and dikes
An elongate, medium-gray, medium-grained, hypidiomorphic granular hornblende-biotite quartz monzodiorite that contains variable amounts of clinopyroxene located in extreme northwest part of Kenai quadrangle, northeast part of Lake Clark quadrangle, and southwest part of Tyonek quadrangle (Nelson and others, 1983; Wilson and others, 2006a, 2009, 2012, in press [Scientific Investivgations Map 2942]). Magmatic flow structures locally present; hornblende and plagioclase are aligned north-northeast. Body is sandwiched between Jurassic plutons on the east and early Tertiary or Late Cretaceous and Eocene plutons on the west, all considered part of the Alaska-Aleutian Range batholith of Reed and Lanphere (1969, 1972). Two samples yielded strongly discordant K/Ar biotite and hornblende ages between 97.5 and 58.8 Ma (Reed and Lanphere, 1973; Nelson and others, 1983)

Source map information

Source map Nelson, W.H., Carlson, Christine, and Case, J.E., 1983, Geologic map of the Lake Clark quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-1114A, 1 sheet, scale 1:250,000.
Symbol KJi
Unit name Cretaceous(?) and Jurassic(?) intrusive rocks -- Quartz monzodiorite
Description Medium-gray, medium-grained, hypidiomorphic granular hornblende-biotite quartz monzodiorite containing variable amounts of clinopyroxene. Flow structures locally present and hornblende and plagioclase is aligned in a north-northeast direction.
Lithology Igneous

Correlated geologic units

Label KJg
Description Granitic rocks and minor monzonite
Geologic age Late-Jurassic to Early-Cretaceous
Geologic setting Intrusive
Lithology Form Importance
Granodiorite < Granitic < Plutonic < Igneous Pluton Major
Diorite < Dioritic < Plutonic < Igneous Dike or sill Minor
Monzonite < Syenitic < Plutonic < Igneous Dike or sill Minor