Marble along the west side of the Coast plutonic complex of Brew and Morrell (1979b)

Unit symbol: Pm
Age range Permian? protolith (298.9 to 252.2 Ma)
Lithology: Metamorphic
Group name: Metamorphic rocks associated with the Coast plutonic complex of Brew and Morrell (1979b)
Light-brown-weathering, massive to laminated, light-, bluish-, and dark-gray marble on Revillagigedo Island (Silberling and others, 1982; Berg and others, 1978, 1988). This marble contains locally conspicuous, dark-green, dark-gray, or rusty-weathering pyritic phyllite and semischist, polymictic sedimentary breccia or conglomerate that has angular to subrounded clasts of basalt, marble, and felsic(?) metatuff in a matrix of green metatuff and dark-gray argillite, schistose fragmental (volcaniclastic?) rocks, and greenish-black basalt dikes and sills (Berg and others, 1988). Marble on Revillagigedo Island and on the mainland east of Admiralty Island (the “Taku terrane”) may not be correlative with Permian carbonate rocks elsewhere in southeast Alaska (the “Alexander terrane”) based its association with Middle Triassic strata not present to the west (Silberling and others, 1982). Rocks of this unit are exposed widely in southeast Alaska west of the Coast Plutonic Complex of Brew and Morrell (1979b); where not mapped separately, are included in unit MzPzss

Source map information

Source map Berg, H.C., Elliott, R.L., and Koch, R.D., 1988, Geologic map of the Ketchikan and Prince Rupert quadrangles, southeastern Alaska: U.S. Geological Survey Miscellaneous Investigations Series Map I-1807, pamphlet, 27 p., scale 1:250,000.
Symbol Pm
Unit name Marble
Description Most of this unit is light brown weathering, massive to laminated, light gray, bluish gray, and dark gray marble. Less abundant, but locally conspicuous other lithologies mapped with it include (a) dark green, dark gray, or rusty weathering pyritic phyllite and semischist, (b) polymictic sedimentary breccia or conglomerate containing relict angular to subrounded clasts of basalt, marble, and felsic(?) metatuff as much as a meter long in a matrix of green metatuff and dark gray argillite, (c) schistose fragmental (volcaniclastic?) rock comprising elongate strongly flattened relict clasts as much as several cm long of quartzite or felsic(?) metavolcanic rocks enclosed by rusty-weathering, fine-grained, pyrite-quartz-muscovite-mariposite(?)-calcite or -dolomite schist, and (d) greenish black basalt dikes and sills. Thin sections of the marble typically show sugary to coarsely garnoblastic aggregates of calcite or dolomite and minor quartz, muscovite, graphite, and pyrite.
Lithology Metamorphic

Correlated geologic units

Label Pm
Description Marble, Taku terrane
Geologic age Permian
Geologic setting Sedimentary, carbonate
Lithology Form Importance
Marble < Metacarbonate < Metasedimentary < Metamorphic Major
Phyllite < Metaclastic < Metasedimentary < Metamorphic Minor
Mafic-hypabyssal < Hypabyssal < Igneous Dike or sill Incidental
Metasedimentary < Metamorphic Incidental