Strelna Metamorphics and related rocks

Unit symbol: PIPsm
Age range early Permian to Middle Pennsylvanian (315.2 to 252.2 Ma)
Lithology: Metamorphic
Group name: Strelna Metamorphics and related rocks
Variably metamorphosed, but largely lower greenschist-facies metasedimentary and metavolcanic rocks that are generally considered a metamorphic equivalent of the Skolai and Mankomen Groups (Richter and others, 2006). Includes the Uranatina River metaplutonic complex of Winkler and others (1981) and the Dadina Schist of Carboniferous and possibly older age exposed near Mount Drum (Richter and others, 1994). Unit includes quartzofeldspathic and quartz-mica schist, which locally has compositional layering reflecting original bedding; greenstone derived from mafic to intermediate volcanic rocks; locally abundant marble interbeds; tectonically emplaced ultramafic rock; and marble lenses, as well as metachert and orthogneiss. Metamorphic grade generally increases to amphibolite facies near contacts with the Uranatina River metaplutonic complex. Tightly folded and pervasively faulted in most localities. Generally undated, the Strelna Metamorphic Complex is on trend with similar strata containing age-diagnostic conodonts in marble (Plafker and others, 1985). Uranatina metaplutonic complex is part of a 10-by-15-km tectonic inclusion in the McHugh Complex that consists of compositionally banded quartz gabbro, amphibolite, and hornblende-biotite dioritic and quartz dioritic orthogneiss. Foliation of the rocks is swirled or tightly folded in many places and large hornblende or hornblende-plagioclase pods have grown in the hinges of many folds. Unit yields Cretaceous and Jurassic cooling ages, as well as a Permian K/Ar age (267±8 Ma) on pegmatite (Winkler and others, 1981) and is known to contain, at least locally, Middle Pennsylvanian metagranodiorite (Plafker and others, 1989). Metamorphic grade of the Strelna Metamorphic Complex increases toward the Chitina Valley batholith and near plutons of the Saint Elias suite (unit KJse) (Richter and others, 2006). The northern part of this unit, locally mapped as the metamorphic complex of Gulkana River (W.J. Nokleberg, written commun., 1997), trends across the northern part of the Gulkana quadrangle and into the northeast part of the Talkeetna Mountains quadrangle. Also see description of the Skolai and Mankomen Groups, undivided (unit PIPms)

Source map information

Source map Csejtey, Bela, Jr., Nelson, W.H., Jones, D.L., Silberling, N.J., Dean, R.M., Morris, M.S., Lanphere, M.A., Smith, J.G., and Silberman, M.L., 1978, Reconnaissance geologic map and geochronology, Talkeetna Mountains quadrangle, northern part of Anchorage quadrangle, and southwest corner Healy quadrangle, Alaska: U.S. Geological Survey Open-File Report 78-558-A, 60 p., 1 sheet, scale 1:250,000.
Symbol Pls
Unit name Marble
Description Forms lenticular interbeds, as much as a few tens of meters thick, within basaltic to andesitic late Paleozoic metavolcanogenic sequence (Pzv). Rock is light gray to white, medium to coarse grained, thick-bedded to massive marble.
Lithology Metamorphic

Correlated geologic units

Label JPzmb
Description Skolai Group, marble, Early Permian to Middle Pennsylvanian
Geologic age Moscovian to Cisuralian
Geologic setting Sedimentary, carbonate
Lithology Form Importance
Marble < Metacarbonate < Metasedimentary < Metamorphic Greenschist Major