Basalt and tuff

Unit symbol: Tpv
Age range Tertiary, Pliocene (5.333 to 1.806 Ma)
Lithology: Igneous - Volcanic
Group name: Younger volcanic rocks, undivided
Olivine basalt lava flows as thick as 10 m and locally diabasic intrusive rocks are found in the northwest corner of the Taylor Mountains quadrangle. These columnar-jointed flows, which form a large tilted plateau, yielded K/Ar ages of 4.62±0.14 Ma (from plagioclase) and 4.72±0.1 Ma (whole rock) (Reifenstuhl and others, 1985); D.C. Bradley (written commun., 2010) reported a whole rock 40Ar/39Ar plateau age of 4.63±0.07 Ma. An outcrop of olivine basalt at Kazik Hill in the northeast Taylor Mountains quadrangle is undated, but also included here. Map unit also includes the Intricate Basalt of Detterman and Reed (1980) in the Iliamna quadrangle, a glassy to porphyritic black to dark-green olivine-augite basalt, which occurs largely in the vicinity of Intricate Bay, but also occurs south of Gibraltar Lake, and includes mafic dikes not shown here. Detterman and Reed (1980) reported K/Ar whole rock dates of 4.4±0.5 and 5.1±1.0 Ma on an olivine basalt dike that cuts the Naknek Formation. Unit also includes Gibraltar Lake Tuff, which has an upper nonwelded member of light-gray to white crystal ash-flow tuff that has a maximum thickness of 152 to 182 m; locally capped by basalt flows of Intricate Basalt. Lower member is at least 300 m thick, consists of light- to medium-gray and tan rhyolitic crystal and lithic welded tuff; locally, interbedded porphyritic rhyolite flows. Detterman and Reed (1980) had little age control; however, based on geomorphic character and comparison with other Tertiary age units, they suggested that the age was more likely Pliocene than Oligocene

Source map information

Source map Hoare, J.M., and Condon, W.H., 1969-1970, Unpublished data.
Symbol Tb
Unit name Extrusive igneous rocks
Description Olivine basalt flows
Lithology Igneous

Correlated geologic units

Label Tib
Description Intricate Basalt
Geologic age Pliocene
Geologic setting Extrusive
Lithology Form Importance
Basalt < Mafic-volcanic < Volcanic < Igneous Flow Major
Andesite < Mafic-volcanic < Volcanic < Igneous Flow Incidental