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 Wilson, F.H., Detterman, R.L., Miller, J.W., and Case, J.E., 1995, Geologic map of the Port Moller, Stepovak Bay, and Simeonof Island quadrangles, Alaska: U.S. Geological Survey Miscellaneous Investigation Map I-2272, 2 sheets, scale 1:250,000.
Symbol QTc
Unit name Contact-metamorphosed rocks
Description Contact-metamorphosed and hydrothermally altered rocks found in mountains east of Mount Dana in Port Moller C-4 1:63,360-scale quadrangle. Protoliths probably consist of, in order of importance, Late Cretaceous Hoodoo Formation (Kh), Tertiary volcanic rocks (Tvu), and Late Cretaceous Chignik Formation (Kc); may also include Tertiary intrusive rocks (Tiu) 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
Lithology Metamorphic

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