Green amphibole-bearing schist

Unit symbol: MzPzgs
Age range Jurassic metamorphism (419.2 to 145 Ma)
Lithology: Metamorphic
Group name: Kisaralik anticlinorium of Box and others (1993) (Togiak-Tikchik Complex)
Schist recrystallized in part to greenschist metamorphic facies mineral assemblage of albite-epidote-chlorite-actinolite. Schist contains interbeds of thin-bedded, white or green metachert that contains white mica-rich laminae (Box and others, 1993); overlain by crystalline limestone, phyllite, and minor amounts of chlorite, graphite, and quartz-sericite schist (Hoare and Coonrad, 1959a). Mapped as Mesozoic to Paleozoic metabasalt and minor metachert (MzPzb) by Box and others (1993); protolith was diabase and basalt that had “trace-element chemical compositions of lavas are similar to modem mid-ocean ridge basalts and range from light REE-depleted to slightly light REE-enriched varieties” (Box and others, 1993). Although protolith age is unknown, it was suggested to be Devonian to Ordovician by Hoare and Coonrad (1959a). Unit is bounded on west by the Golden Gate Fault; nearshore facies of the Kuskokwim Group (Kkn) depositionally overlie unit at the north end of its exposure. Age of metamorphism may be Late Jurassic based on a K/Ar age of 146.0±15.0 Ma on actinolite. MzPzgs is physically separate from the other rocks of this group; Box and others (1993) inferred that a thrust fault placed the other rocks of the anticlorinorium structurally over this schist

Source map information

Source map Box, S.E., Moll-Stalcup, E.J., Frost, T.P., and Murphy, J.M., 1993, Preliminary geologic map of the Bethel and southern Russian Mission quadrangles, southwestern Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-2226-A, 1 sheet, scale 1:250,000.
Symbol MzPzb
Unit name Metabasalt and minor metachert, Goodnews terrane
Description Weakly to strongly foliated metabasalt having variable recrystallization to greenschist-facies assemblage of albite-epidote-chlorite-actinolite. Interbedded sequences of thin-bedded, white to green metachert having white mica-rich laminae. Mid-ocean ridge chemical (REE) affinities.
Lithology Metamorphic

Correlated geologic units

Label Jgs
Description Metabasalt and minor metachert, southwest Alaska
Geologic age Paleozoic to Jurassic
Geologic setting Extrusive
Lithology Form Importance
Metavolcanic < Metaigneous < Metamorphic Greenschist Indeterminate, major