Undivided granitic rocks

Unit symbol: Tpgr
Age range Tertiary, late Paleocene (66 to 56 Ma)
Lithology: Igneous - Plutonic
Group name: Granitic rocks of southern and interior Alaska
Predominantly medium-grained composite plutons of granite and quartz monzonite and lesser granodiorite and quartz syenite. Biotite is the chief mafic mineral and hornblende is locally present, especially in the granodiorite phases. Muscovite is a common component of the granite. Unit is widespread, although the bulk of the exposure is in the western Alaska Range and Tyonek quadrangle or spatially associated with the Alaska-Aleutian Range batholith of Reed and Lanphere (1973) in the Lake Clark and Iliamna quadrangles. It is primarily distinguished from unit Tkg by age determinations. Unit includes the Styx River batholith of Reed and Elliott (1970), rocks of map units Ti7, Ti10, and Ti11 of Nelson and others (1983), much of the McKinley series of Reed and Nelson (1980) and unit Tbgd of Csejtey and others (1978). Outliers occur in Unalakleet and Table Mountain quadrangles. In the Lime Hills and western Tyonek quadrangles, it is difficult to distinguish between this map unit and unit TKg; without additional mapping and data, the density of lithologically similar plutons makes distinction of these two units especially difficult

Source map information

Source map Haeussler, P.J., 2007, Unpublished data.
Symbol Tpd
Unit name Biotite diorite
Description Diorite, quartz diorite, quartz monzodiorite and quartz monzonite in a large compositionally variable pluton which outcrops over an area of about 7 square miles (11 km2 ) (Solie and others, 1991). Generally coarse- to medium-grained, a fine-grained variant is also found. More mafic phases contain olivine, both clino- and orthopyroxene, and biotite, whereas more quartz- and potassium-feldspar-rich phases contain amphibole and/or biotite (Solie and others, 1991)
Lithology Igneous

Correlated geologic units

Label Tpd
Description Biotite diorite
Geologic age Paleocene
Geologic setting Intrusive, tonalite-granodiorite
Lithology Form Importance
Diorite < Dioritic < Plutonic < Igneous Pluton Indeterminate, major
Quartz-diorite < Dioritic < Plutonic < Igneous Pluton Indeterminate, major
Quartz-monzodiorite < Dioritic < Plutonic < Igneous Pluton Indeterminate, major
Quartz-monzonite < Syenitic < Plutonic < Igneous Pluton Indeterminate, major