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 Weber, F.R., Foster, H.L., Keith, T.E.C., and Dusel-Bacon, Cynthia, 1978, Preliminary geologic map of the Big Delta quadrangle, Alaska: U.S. Geological Survey Open-File Report 78-529A, scale 1:250,000.
Symbol Pzsg
Unit name Semischist, greenschist, quartzite, phyllite, marble, and greenstone
Description Semischist or sheared grit; greenish gray or gray and fine to coarse grained; very quartzitic to very feldspathic; clear, gray, or bluish-gray quartz grains 1 to 5 mm in diameter characteristic; interlayered with quartz-chlorite mica schist and others combinations of greenschist rocks, tan quartzite, gray and tan phyllite, marble, and greenstone. Possibly equivalent to the Totatlinika Schist in the northern Alaska Range.
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