Cenozoic evolution of the continental margin of Oregon and Washington

Snavely, Parke Detweiler; Wells, Ray E.

doi:10.3133/ofr91441b

Cited by 30 publications

(24 citation statements)

References 32 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Middle Eocene submarine and subaerial basalts that are overlain by Middle to Upper Eocene sedimentary rocks (Snavely and Wells, 1996). The basalts, which are interbedded with continental margin sediments in a series of basins, have individual formation names (Roseburg, Siletz River, Crescent, and Metchosin) but are collectively known as Siletzia (Fig.…”

Section: Introductionmentioning

confidence: 99%

Petrology of the Grays River volcanics, southwest Washington: Plume-influenced slab window magmatism in the Cascadia forearc

Chan

Tepper

Nelson

2012

Geological Society of America Bulletin

View full text Add to dashboard Cite

The Grays River volcanics are part of the Coast Range basalt province and consist of ~3500 m of tholeiitic basalt fl ows and volcani clastic rocks that erupted in the Cascadia forearc from 42 to 37 Ma. Chemical and isotopic data, combined with migration of the location of magmatism through time, indicate that Grays River volcanics magmatism was related to subduction of a plumeinfl uenced spreading ridge that produced a northward-migrating slab window. Involvement of a mantle plume source is indicated by ocean-island basalt (OIB)-like incompatible element enrichments and radiogenic Pb isotopic compositions ( 206 Pb/ 204 Pb > 19.3).These Pb isotope data are distinct from most Cascade arc rocks and from Cascadia sediment, but they overlap with compositions of other Coast Range basalts. A slab window setting accounts for the northward-younging age progression of the Grays River volcanics as well as geochemical traits, including low B/Be, that indicate the Grays River magmas ascended through the mantle wedge and subducting slab without acquiring an arc signature. Differentiation of Grays River magmas was dominated by clinopyroxene fractionation, which resulted in evolved compositions (Mg# = 59-32), low Sc contents, and Sr contents that increase with fractionation. Geochemical differences between the Grays River volcanics and other Cascadia forearc volcanic units that range from ca. 55 Ma (Crescent Basalts) to <3 Ma (Boring Lavas) were mainly caused by transient changes in tectonic setting (i.e., arrival of a mantle plume, ridge subduction) and do not record progressive chemical modifi cation of the mantle wedge.

show abstract

Section: Introductionmentioning

confidence: 99%

Petrology of the Grays River volcanics, southwest Washington: Plume-influenced slab window magmatism in the Cascadia forearc

Chan

Tepper

Nelson

2012

Geological Society of America Bulletin

View full text Add to dashboard Cite

show abstract

“…The tectonics of the Pacific Northwest region are dominated by the oblique, northeastward subduction of the Juan de Fuca plate beneath western North America. Subduction of oceanic lithosphere during the Tertiary has led to the formation of two major geologic provinces in the region: the Coast Range province on the west, which includes the Olympic subduction complex (OSC) plus the Puget Lowland, and the Cascade province on the east (Figure 1) [ Brandon and Calderwood , 1990; Snavely and Wells , 1996].…”

Section: Introductionmentioning

confidence: 99%

Crustal structure and relocated earthquakes in the Puget Lowland, Washington, from high‐resolution seismic tomography

et al. 2002

View full text Add to dashboard Cite

The availability of regional earthquake data from the Pacific Northwest Seismograph Network (PNSN), together with active source data from the Seismic Hazards Investigation in Puget Sound (SHIPS) seismic experiments, has allowed us to construct a new high‐resolution 3‐D, P wave velocity model of the crust to a depth of about 30 km in the central Puget Lowland. In our method, earthquake hypocenters and velocity model are jointly coupled in a fully nonlinear tomographic inversion. Active source data constrain the upper 10–15 km of the model, and earthquakes constrain the deepest portion of the model. A number of sedimentary basins are imaged, including the previously unrecognized Muckleshoot basin, and the previously incompletely defined Possession and Sequim basins. Various features of the shallow crust are imaged in detail and their structural transitions to the mid and lower crust are revealed. These include the Tacoma basin and fault zone, the Seattle basin and fault zone, the Seattle and Port Ludlow velocity highs, the Port Townsend basin, the Kingston Arch, and the Crescent basement, which is arched beneath the Lowland from its surface exposure in the eastern Olympics. Strong lateral velocity gradients, consistent with the existence of previously inferred faults, are observed, bounding the southern Port Townsend basin, the western edge of the Seattle basin beneath Dabob Bay, and portions of the Port Ludlow velocity high and the Tacoma basin. Significant velocity gradients are not observed across the southern Whidbey Island fault, the Lofall fault, or along most of the inferred location of the Hood Canal fault. Using improved earthquake locations resulting from our inversion, we determined focal mechanisms for a number of the best recorded earthquakes in the data set, revealing a complex pattern of deformation dominated by general arc‐parallel regional tectonic compression. Most earthquakes occur in the basement rocks inferred to be the lower Tertiary Crescent formation. The sedimentary basins and the eastern part of the Olympic subduction complex are largely devoid of earthquakes. Clear association of hypocenters and focal mechanisms with previously mapped or proposed faults is difficult; however, seismicity, structure, and focal mechanisms associated with the Seattle fault zone suggest a possible high‐angle mode of deformation with the north side up. We suggest that this deformation may be driven by isostatic readjustment of the Seattle basin.

show abstract

“…They crop out in a northward-dipping homoclinal sequence along the northwestern coast of the Olympic Peninsula, part of almost 6000 m of Eocene to Miocene marine sediments. The entire sedimentary sequence unconformably overlies pillow basalts and breccias of the Crescent volcanics, which were exotic oceanic ridge and seamount terranes that accreted to North America in the early Eocene [24][25][26]. The Makah Formation is conformably overlain by the Oligocene Pysht Formation, which is better exposed in the north-central coast of the Olympic Peninsula between Clallam Bay and Lyre River [27] to the east of our study area.…”

Section: Geologic Settingmentioning

confidence: 99%

Magnetostratigraphy and Tectonic Rotation of the Eocene-Oligocene Makah and Hoko River Formations, Northwest Washington, USA

Prothero

Draus

Burns

2009

International Journal of Geophysics

View full text Add to dashboard Cite

The Eocene-Oligocene Makah Formation and subjacent middle Eocene Hoko River Formation of the northwestern Olympic Peninsula, Washington, yield mollusks, crustaceans, foraminifera, and early neocete whales; their age has never been precisely established. We sampled several sections; most samples showed a stable single-component remanence held largely in magnetite and passed a Class I reversal test. The upper Refugian (late Eocene) and lower Zemorrian (early Oligocene) rocks at Baada Point correlate with Chron C13r (33.7-34.7 Ma) and Chron C12r (30-33 Ma). The Ozette Highway section of the Makah Formation spanned the early Refugian to late Refugian, with a sequence that correlates with Chrons C15r-C13r (33.7-35.3 Ma), and a long reversed early Zemorrian section that correlates with Chron C12r (30-33 Ma). The type section of the Hoko River Formation correlates with Chron C18r (40.0-41.2 Ma). The area sampled shows about 45• of post-Oligocene counterclockwise tectonic rotation, consistent with results obtained from the Eocene-Oligocene rocks in the region.

show abstract

Cenozoic evolution of the continental margin of Oregon and Washington

Cited by 30 publications

References 32 publications

Petrology of the Grays River volcanics, southwest Washington: Plume-influenced slab window magmatism in the Cascadia forearc

Petrology of the Grays River volcanics, southwest Washington: Plume-influenced slab window magmatism in the Cascadia forearc

Crustal structure and relocated earthquakes in the Puget Lowland, Washington, from high‐resolution seismic tomography

Magnetostratigraphy and Tectonic Rotation of the Eocene-Oligocene Makah and Hoko River Formations, Northwest Washington, USA

Contact Info

Product

Resources

About