Contact metamorphosed and hydrothermally altered rocks

Unit symbol: QTm
Age range Quaternary or late Tertiary (5.333 to 0.0117 Ma)
Lithology: Metamorphic
Group name: Contact metamorphosed and hydrothermally altered rocks
Contact-metamorphosed and hydrothermally altered rocks found on the southwest Alaska Peninsula and Umnak Island in the Aleutian Islands. On the Alaska Peninsula, protoliths probably consist of, in order of importance, Late Cretaceous Hoodoo Formation (unit Khk), Tertiary volcanic rocks (unit Tvu), and Late Cretaceous Chignik Formation (unit Kcs); may also include Tertiary intrusive rocks (unit Tmi or Tgw) at lower elevations. Pervasive alteration prevents separation of altered rocks into their respective units. Rocks are hard, very fine-grained, and intensely fractured; sulfide mineralization is common, and resultant iron staining is ubiquitous on weathered surfaces (Wilson and others, 1995). On central Umnak Island, volcanic rocks are locally intensely silicified, potassium feldspathized, and hydrothermally altered over a large area (Byers, 1959)

Source map information

Source map Byers, F.M., Jr., 1959, Geology of Umnak and Bogoslof Islands, Aleutian Islands, Alaska: U.S. Geological Survey Bulletin 1028-L, p. 267-369, 3 plates, scales 1:63,360, 1:96,000, and 1:300,000.
Symbol QTvq
Unit name Volcanic rocks of central Umnak
Description Intensely silicified, potassium feldspathized rocks
Lithology Igneous

Correlated geologic units

Label QTc
Description Quaternary or Tertiary metamorphic rocks, particularly in Mt. Dana area on Port Moller map
Geologic age Pliocene to Pleistocene
Geologic setting Metamorphic, undivided
Lithology Form Importance
Hornfels < Granoblastic < Metamorphic Hornfels Indeterminate, major