Four Winds complex of Gilbert and others (1987) and similar rocks

Unit symbol: SZfw
Age range Silurian to Neoproterozoic (635 to 419.2 Ma)
Lithology: Metamorphic
Group name: Four Winds complex of Gilbert and others (1987), Retreat Group, and orthogneiss
Consists of a variety of rocks, including interbedded black phyllite, mafic and felsic schist, metachert and medium-gray marble, amphibolite, greenschist, and greenstone; also includes sheared metabasalt and orthogneiss along the west side of Chilkat Inlet and the Chilkat River. Gilbert and others (1987) divided these rocks into four informal units that consist of intercalated metasedimentary and metavolcanic rocks, metabasite, metavolcanic rocks, and gneiss. For partially contiguous rocks to the south in the Skagway quadrangle, Redman and others (1985) used the informal term Cheetdeekahyu group. According to Gilbert and others (1987), metamorphic grade of the Four Winds complex increases to the northeast from greenschist to amphibolite facies. Gilbert and others (1987) suggested that the Four Winds complex is overlain by Mississippian to Devonian age rocks, and hence assigned a pre-Devonian age. Karl and others (2006) report a U/Pb TIMS age of 455±5 Ma from zircon in a metamorphosed(?) felsic dike within the complex on Mount Cheetdeekahyu. They also dated a xenocrystic zircon from the dike that yielded a concordant age of 544±9 Ma, which is similar to the age of orthogneiss that intrudes the Retreat Group at False Point Retreat on Admiralty Island, as well as other orthogneiss bodies that intrude schist of the Wales Group on Prince of Wales Island

Source map information

Source map Gilbert, W.G., 1988, Preliminary geology and geochemistry of the north Chilkat Range: Alaska Division of Geological and Geophysical Surveys Report of Investigations 88-8, 2 sheets, scale 1:36,200.
Symbol Pzam
Unit name Argillaceous marble
Description Light gray, very argillaceous schistose marble, and buff weathering, tan calc-schist and calc-phyllite. Commonly contains quartz segregations up to 15 cm thick. Contains minor intervals of muscovite schist (metatuff), and metabasite, argillaceous marble, and black phyllite, in intervals up to 3 m thick.
Lithology Metamorphic

Correlated geologic units

Label Pzfw
Description Four Winds Complex, undivided
Geologic age Neoproterozoic to Silurian
Geologic setting Metamorphic, undivided
Lithology Form Importance
Phyllite < Metaclastic < Metasedimentary < Metamorphic Major
Gneiss < Metamorphic Indeterminate, major
Marble < Metacarbonate < Metasedimentary < Metamorphic Indeterminate, major
Metasiltstone < Metaclastic < Metasedimentary < Metamorphic Indeterminate, major
Quartzite < Metaclastic < Metasedimentary < Metamorphic Indeterminate, major
Schist < Metamorphic Indeterminate, major