Dikes and subvolcanic rocks

Unit symbol: TKhi
Age range Tertiary and (or) Cretaceous (83.6 to 56 Ma)
Lithology: Igneous - Plutonic
Group name: Undivided dikes and sills
Widely distributed in western Alaska, unit consists of a wide variety of shallow intrusive rocks including rhyolite, dacite, trachyte, and andesite plugs, domes, sills, and dikes, and larger, more coarsely crystalline bodies of granite, granodiorite, tonalite, and monzonite porphyry (Patton and others, 2009; Patton and others, in press [Scientific Investivgations Map 3015]). Typical rock is composed of a fine-grained felsic groundmass with phenocrysts of plagioclase, quartz, biotite, and hornblende. Unit forms numerous large sills, dikes, and domes intruding Cretaceous and older sedimentary rocks primarily in the Iditarod, Sleetmute, Russian Mission, northwestern Holy Cross, and northeastern Kwiguk quadrangles. Limited age control from K/Ar, 40Ar/39Ar, and U/Pb techniques in southwest Alaska suggests an age range between about 72 and 60 Ma. Unit is compositionally similar to and, where age control exists, is also similar in age to units TKg and TKgd. Unit is texturally transitional between TKg, TKgd, and unit TKv. Unit is also found less commonly in the Selawik, Bettles, Hughes, Lime Hills, Dillingham, and Lake Clark quadrangles. In the Selawik, Bettles, and Hughes quadrangles, age control is lacking, but association with mid-Cretaceous plutons suggests that these small intrusions may be older than those in southwest Alaska

Source map information


Correlated geologic units

Label TKgp
Description Hypabyssal granite porphyry dikes, sills, and plugs
Geologic age Campanian to Paleocene
Geologic setting Extrusive
Lithology Form Importance
Hypabyssal-rhyolite < Felsic-hypabyssal < Hypabyssal < Igneous Dike or sill Indeterminate, major