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Geology, Petrology, And Paleomagnetism Of Eocene Basalts From The Black Hills, Washington Coast Range, Brian R. Globerman

WWU Graduate School Collection

Geologic mapping in the Black Hills area strongly suggests that the middle Eocene basalts of the Crescent Formation and over- lying upper Eocene and Oligocene sedimentary rocks constitute a structurally coherent terrane that is bounded by northeast- and northwest-trending faults. I interpret the Black Hills as a homocline which dips about 10° to 15° to the west. Units within the block are commonly cut by normal and reverse faults, but are not appreciably folded.

Major- and trace-element geochemical analyses indicate that the Black Hills suite is co-magmatic, and is composed of hyper- sthene-normative tholeiites which were apparently derived by plagioclase …