Metavolcanic rocks and sills

Unit symbol: Dv
Age range Devonian (419.2 to 358.9 Ma)
Lithology: Metamorphic
Group name: Volcanic rocks and sills
Mafic and lesser felsic metavolcanic rocks and greenstone sills interlayered in Hunt Fork Shale and Beaucoup Formation (Brosgé and Reiser, 2000) and, locally, in the Kanayut Conglomerate (Mull and Werdon, 1994). It is mappable as two separate metavolcanic units in most places: a mafic metavolcanic and a felsic metavolcanic unit. Mafic unit consists of pillow basalt, amygdaloidal basalt, and basalt capped by tuffaceous limestone, commonly schistose and altered to calcic greenstone; may, in part, have been olivine basalt flows, about 10 to 80 m thick (Brosgé and others, 1979). Unit also includes younger (presumed Carboniferous) mafic to intermediate metavolcanic rocks in the Howard Pass quadrangle that are associated with limestone of the Lisburne Group and the Nuka Formation (Mull and Werdon, 1994). Felsic rocks, a minor part of the unit, include metamorphosed crystal and lithic tuff, volcanic breccia, and minor porphyry of rhyolitic compositions, now mostly recrystallized to fine crystalline quartz-sericite schist (Brosgé and Reiser, 2000). This unit is distinct form the Ambler sequence (unit Das) in being typically associated with the Hunt Fork Shale (unit Degh) and in being a dominantly mafic unit

Source map information

Source map Brosge', W.P., Reiser, H.N., Dutro, J.T., Jr., and Detterman, R.L., 1979, Bedrock geologic map of the Phillip Smith Mountains quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-879-B, 2 sheets, scale 1:250,000.
Symbol mr
Unit name Mafic Rocks
Description Orange and dark green weathering clinopyroxene gabbro and diabase, commonly altered to calcitic greenstone; commonly schistose near margins. Occur in bodies 1-100m thick, some with fine-grain chilled margins, or in contact with hornfels in the adjacent slate.
Lithology Igneous

Correlated geologic units

Label Dvt
Description Basaltic and andesitic flows, tuff, breccia, and volcanic conglomerate altered to greenstone, interbedded in Hunt Fork Shale
Geologic age Devonian
Geologic setting Extrusive
Lithology Form Importance
Greenstone < Metaigneous < Metamorphic Major
Andesite < Mafic-volcanic < Volcanic < Igneous Flow Indeterminate, major
Andesite < Mafic-volcanic < Volcanic < Igneous Volcaniclastic Indeterminate, major