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 Winkler, G.R., Silberman, M.L., Grantz, Arthur, Miller, R.J., and MacKevett, E.M., Jr., 1981, Geologic map and summary geochronology of the Valdez quadrangle, southern Alaska: U.S. Geological Survey Open-File Report 80-892-A, 2 sheets, scale 1:250,000. and modifications by Winkler, 1997).
Symbol Pzs
Unit name Skolai Group -- greenstone unit
Description Diverse Upper Paleozoic volcanic, volcaniclastic, and marine sedimentary rocks. Unit consists largely of two lithologies, map unit Pzs is dark, greenish-gray poorly bedded greenstone, characterized by prehnite-pumpellyite mineral assemblages, locally retaining relict pillows and map unit Pzm is subordinate light- or medium-gray and buff calcareous rocks, mostly recrystallized to marble but containing scanty fragments of fossils, interbedded with minor dark-gray calcareous siltstone and shale.
Lithology Metamorphic

Correlated geologic units

Label JPam
Description Meta-hornblende andesite, Late Paleozoic(?); Amphibolite and quartz diorite, Middle to Early Jurassic metamorphic age; also Skolai Group, greenstone
Geologic age Paleozoic
Geologic setting Extrusive
Lithology Form Importance
Amphibolite < Metamorphic Greenschist Indeterminate, major
Amphibolite < Metamorphic Zeolitic (prehnite-pumpellyite) Indeterminate, major
Amphibolite < Metamorphic Amphibolite Indeterminate, major
Marble < Metacarbonate < Metasedimentary < Metamorphic Greenschist Indeterminate, major
Mica-schist < Schist < Metamorphic Zeolitic (prehnite-pumpellyite) Indeterminate, major