Upper Jurassic-Lower Cretaceous volcanic rocks

Predominantly volcanic rocks, mostly metamorphosed to greenstone and greenschist; includes some sedimentary rocks
State Washington
Name Upper Jurassic-Lower Cretaceous volcanic rocks
Geologic age Jurassic-Cretaceous on San Juan Islands; possibly Eocene in King County
Lithologic constituents
Major
Metamorphic > Metaigneous > GreenstoneIncludes greenstone tuff of Lopez structural complex and greenstone, metadiabase, metatuff, and serpentinite of Lummi formation; relative abundance unknown.
Igneous > VolcanicIncludes andesite flows, tuff, and breccia, basalt, and dacite of outcrop in King County and possibly dacite, andesite, and basalt of Fidalgo complex. Also includes Eagle Cliff basalt.
Metamorphic > Schist (Greenschist)
Minor
Igneous > PlutonicIncludes gabbro and possibly diorite, trondhjemite, granite, and quartz diorite of Fidalgo complex.
Incidental
Sedimentary > ClasticIncludes conglomerate and sandstone in King County and limestone in Lummi formation.
Comments Volcanic rocks in King County include andesite flows, tuff, and breccia with minor dacite and basalt, and minor volcaniclastic sandstone, conglomerate, and siltstone (Tabor and others, 1993, Dragovich and others, 2002). Outcrops on San Juan Islands consist mostly of greenstone with metasedimentary and metavolcanic rocks as well as unmetamorphosed igneous rock (Dragovich and others, 2002).
Stratigraphic units Eagle Cliff porphyrite; Lummi formation (in part); Lopez structural complex (in part); Fidalgo complex (in part)
References

Huntting, M.T., Bennett, W.A.G., Livingston, V.E.Jr., and Moen, W.S., 1961, Geologic Map of Washington: Washington Division of Mines and Geology, scale 1:500,000.

Brandon, M.T., 1989, Geology of the San Juan-Cascade Nappes, northwestern Cascade Range and San Juan Islands, in Joseph, N. L. (Ed.), Geologic Guidebook for Washington and Adjacent Areas: prepared for the 85th Annual Meeting of the Cordilleran Section, Geological Society of America, May 8-11, 1989, Spokane, Washington: Washington Division of Geology and Earth Resource Infomation Circular 86, p. 137-162.

Tabor, R.W., Frizzell, V.A.,Jr., Booth, D.B., Waitt, R.B., Whetten, J.T., Zartman, R.E., 1993, Geologic Map of the Skykomish River 30- by 60-Minute Quadrangle, Washington: U. S. Geological Survey Miscellaneous Investigations Series Map I-1963, scale 1:100,000.

Dragovich, J.D., Logan, R.L., Schasse, H.W., Walsh, T.J., Lingley, W.S., Jr., Norman, D.K., Gerstel, W.J., Lapen, T.J., Schuster, J.E., Meyers, K.D., 2002, Geologic Map of Washington-Northwest Quadrant: Washington Division of Geology and Earth Resources Geologic Map GM-50, scale 1:250,000.

Garver, J., 1988, Stratigraphy, depositional setting, and tectonic significance of the clastic cover to the Fidalgo Ophiolite, San Juan Islands, Washington: Canadian Journal of Earth Sciences, v. 25, p. 417-432.

NGMDB product
Counties King - San Juan - Skagit - Whatcom