Metagabbro and metasedimentary rocks

Unit symbol: Pznp
Age range Paleozoic? (541 to 358.9 Ma)
Lithology: Metamorphic
Group name: Metagabbro and metasedimentary rocks (Nome Complex)
Metagabbro and poorly exposed metasedimentary rocks on the western side of the Kigluaik Mountains exposed in tors and rubble (Till and others, 2011). Unit description derived from Till and others (2011) for their unit Pznp. Coarse-grained metagabbro bodies form flat-topped hills generally less than a kilometer across; one body exposed along sea cliffs is 9 km long. Metasedimentary rocks include metagraywacke and tuffaceous metasedimentary rocks and both metaigneous and metasedimentary rocks preserve original igneous and sedimentary features. Metagabbro is geochemically similar to metabasite from Till’s units Ocs and DOx (Ayuso and Till, 2007; units Ocs and DOnx, here). The geometries of outcrop-scale structures are similar to those in the more completely recrystallized and deformed part of the Nome Complex. Hannula and others (1995) reported three pumpellyite- and actinolite-bearing samples from northern parts of the unit and one crossite-bearing sample from the central part, which indicate that metamorphic grade increases from northwest to southeast within the unit. The contact between Till and others’ (2011) units Pznp and Ocs to the southwest corresponds to the garnet isograd of Hannula and others (1995). |np may be equivalent to Ocs

Source map information

Source map Till, A.B., Dumoulin, J.A., Werdon, M.B., and Bleick, H.A., 2011, Bedrock geologic map of the Seward Peninsula, Alaska, and accompanying conodont data: U.S. Geological Survey Scientific Investigations Map 3131, 2 sheets, scale 1:500,000, 1 pamphlet, 75 p., and database, available at http://pubs.usgs.gov/sim/3131/.
Symbol Pznp
Unit name Metagabbro and metasediments, Nome Complex
Description Massive tors and rubble piles of metagabbro and poorly exposed metasedimentary rocks on the western side of the Kigluaik Mountains. Metagabbro bodies form flat-topped hills generally less than a kilometer across; one body exposed along sea cliffs is 9 km long. Metasedimentary rocks are poorly exposed and include metagraywacke and tuffaceous metasediments. Original igneous and sedimentary features are preserved in the unit. In thin section, metagabbro is coarse grained and partially to completely recrystallized to actinolite, epidote, chlorite, titanite, albite and quartz (Hannula and others, 1995; Till, unpublished data). The metagabbros are geochemically similar to metabasites from units Ocs and DOx (Ayuso and Till, 2007). The geometries of outcrop-scale structures are similar to those in the more completely recrystallized and deformed part of the Nome Complex. Hannula reports three pumpellyite and actinolite bearing samples from northern parts of the unit and one crossite-bearing sample from the central part, which indicates that metamorphic grade increases from northwest to southeast within the unit. The contact between Pznp and Ocs to the southwest corresponds to the garnet isograd of Hannula and others (1995). |np may be equivalent to Ocs. Equivalent to unit "Pzmvu" of Hannula and others (1995)
Lithology Metamorphic

Correlated geologic units

Label Pzng
Description Nome Complex metagabbro and metasedimentary rocks
Geologic age Paleozoic
Geologic setting Intrusive, gabbro
Lithology Form Importance
Metagabbro < Metaintrusive < Metaigneous < Metamorphic Indeterminate, major
Metasedimentary < Metamorphic Indeterminate, major