Geologic Map of Alaska: Wrangell Lava

Wrangell Lava

Unit symbol:	Twv
Age range	Tertiary, Pliocene to Oligocene (33.9 to 1.806 Ma)
Lithology:	Igneous - Volcanic
Group name:	Volcanic rocks, undivided

Consists of basaltic andesite, andesite, and dacite lava flows; andesitic lahar deposits and andesite to dacite porphyry, diorite, and quartz diorite. This is the older part of the Wrangell Lava in the McCarthy and Nabesna quadrangle, exposed on either side of the Totshunda Fault and in the adjacent Yukon. Includes the Sonya Creek and other Tertiary volcanic centers. Includes rhyolitic rocks, domes, hypabyssal, and plutonic rocks (Richter and others, 2006). K/Ar ages of volcanic rocks range between 26.3±0.8 and 8.8±0.9 Ma, whereas intruding plutons have K/Ar ages that range from 9.4±0.7 to 3.41±0.46 Ma

Source map information

Source map	Richter, D.H., Preller, C.C., Labay, K.A., and Shew, N.B., 2006, Geology of Wrangell-Saint Elias National Park and Preserve, southcentral Alaska: U.S. Geological Survey Scientific Investigations Series Map SIM-2877, 15 p., 1 sheet, scale 1:350,000.
Symbol	Th
Unit name	Hypabyssal rocks
Description	Dacite, andesite, and rhyodacite porphyry. Typically strongly porphyritic. Correlates with younger porphyry of Nabesna quadrangle and with hypabyssal rocks associated with the Wrangell Lava in Alaska and Canada. Subdivision of unit Th of MacKevett (1978) south of range divide and Chitna River valley
Lithology	Igneous

Correlated geologic units

Label	Twd
Description	Wrangell Lava, dome and hypabyssal rocks
Geologic age	Pliocene
Geologic setting	Extrusive

Lithology	Form	Importance
Hypabyssal-dacite < Felsic-hypabyssal < Hypabyssal < Igneous	Dome	Indeterminate, major
Hypabyssal-dacite < Felsic-hypabyssal < Hypabyssal < Igneous	Dome	Indeterminate, major
Hypabyssal-rhyolite < Felsic-hypabyssal < Hypabyssal < Igneous	Dome	Indeterminate, major
Andesite < Mafic-volcanic < Volcanic < Igneous	Dome	Minor