Totatlanika Schist

Unit symbol: MDts
Age range Early Mississippian to Late Devonian (393.3 to 346.7 Ma)
Lithology: Metamorphic
Group name: Totatlanika Schist (Yukon-Tanana crystalline complex)
Low-grade, multiply-deformed, locally mylonitic assemblage of gritty semischist that contains clear to bluish-gray quartz “eyes,” chloritic quartzo-feldspathic schist and augen gneiss, phyllitic schist and semischist, phyllite, metavolcanic rocks, quartzite, marble, and greenstone. Porphyritic volcanic and sedimentary textures preserved in places; metavolcanic compositions range from mafic to felsic. Fossil age is poorly defined; conodonts collected from one marble interbed were Middle Devonian to Early Mississippian, and crinoids, corals, and gastropods were less precisely dated (Wahrhaftig, 1968). Meta-andesite from the northeastern Big Delta quadrangle yields an upper intercept U/Pb zircon age of 375 Ma that is interpreted as an extrusive age of the protolith (Dusel-Bacon and others, 1993; revised to 374±3 Ma, Cynthia Dusel-Bacon, written commun., 2014). Dusel-Bacon and others (2006) report U/Pb (SHRIMP) zircon ages between 372±3 and 360±5 Ma for meta-igneous rocks included in the Totatlanika Schist. Unit consists of the Totatlanika Schist of the Fairbanks and Healy quadrangles (Péwé and others, 1966; Csejtey and others, 1992), various units of the Totatlanika Schist in the Chena River area (Smith and others, 1994), unit Pzsg of Weber and others (1978) in the Big Delta quadrangle, and the blastomylonite subunit of unit PzpCs of Foster (1992)

Source map information

Source map Csejtey, Bela, Jr., Mullen, M.W., Cox, D.P., and Stricker, G.D., 1992, Geology and geochronology of the Healy quadrangle, south-central Alaska: U.S. Geological Survey Miscellaneous Investigations Series Map I-1961, 63 p., 2 sheets, scale 1:250,000.
Symbol MDt
Unit name Totatlanika Schist
Description Predominantly metavolcanic and metavolcaniclastic (both felsic and mafic), and subordinate amounts of intercalated metasedimentary rocks such as black pelitic schist, and at one locality a thin interbed of fossiliferous marble.
Lithology Metamorphic

Correlated geologic units

Label MDt
Description Totatlanika Schist, metavolcanic and metavolcaniclastic rocks, Early Mississippian to Middle Devonian,
Geologic age Middle-Devonian to Early-Mississippian
Geologic setting Metamorphic, undivided
Lithology Form Importance
Metavolcanic < Metaigneous < Metamorphic Major
Pelitic-schist < Metaclastic < Metasedimentary < Metamorphic Minor
Marble < Metacarbonate < Metasedimentary < Metamorphic Incidental