Schist of the Telsitna River

Unit symbol: Pxqm
Age range Proterozoic (1600 to 541 Ma)
Lithology: Metamorphic
Group name: Basement of the White Mountain sequence
Chiefly pelitic and quartzose metasedimentary rocks of greenschist facies exposed in west-central Alaska in the northeastern Medfra, southeastern Ruby and southwestern Kantishna River quadrangles. Micaceous quartzite and quartz-chlorite schist grade into quartz-muscovite-biotite-garnet schist; calc-schist and marble are subordinate. Unit locally includes small bodies of greenstone and greenschist-facies metabasite, granitic gneiss, and metamorphosed quartz porphyry. The porphyry is fine-grained, foliated, and banded felsic volcanic rock composed of large phenocrysts of embayed quartz and plagioclase in a very fine-grained quartzo-feldspathic groundmass that has a distinct micaceous overprint. Zircon fractions from two suites of samples of metamorphosed quartz porphyry yielded upper intercept ages of 850±30 Ma and 1,265±50 Ma, interpreted to be crystallization ages (Patton and others, 1980, 2009). Metamorphic minerals from the schist yield K/Ar isotopic cooling ages that range from 921 to 284.2 Ma (Patton and others, 2009), which indicate that this terrane of metamorphic rocks likely did not experience the mid-Cretaceous metamorphism commonly seen in other metamorphic rocks in Alaska

Source map information

Source map Patton, W.W., Jr., Moll, E.J., Dutro, J.T., Jr., Silberman, M.L., and Chapman, R.M., 1980, Preliminary geologic map of the Medfra quadrangle, Alaska: U.S. Geological Survey Open-File Report 80-811A, 1 sheet, scale 1:250,000.
Symbol PzpCv
Unit name Metavolcanic rocks
Description Tan, light-gray, pink, and green banded fine-grained felsic volcanic rocks having well-developed foliation. Chiefly porphyry composed of large phenocrysts of embayed quartz and plagioclase in a very fine grained quartzo-feldspathic groundmass which has a distinct micaceous overprint.
Lithology Metamorphic

Correlated geologic units

Label YZnv
Description Felsic metavolcanic rocks of Nixon Fork basement
Geologic age Mesoproterozoic to Tonian
Geologic setting Extrusive
Lithology Form Importance
Metavolcanic < Metaigneous < Metamorphic Major