Preliminary bedrock geologic map of the Waldport and Tidewater quadrangles, Oregon

Snavely, Parke Detweiler; MacLeod, N.S.; Wagner, H.C.

doi:10.3133/ofr72351

Cited by 3 publications

(4 citation statements)

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“…Snavely and Baldwin (1948) and Snavely et al (1968Snavely et al ( , 1976aSnavely et al ( , 1976bSnavely et al ( , 1976c mapped and described the type area of the SRV between Newport and Corvallis, Oregon (Fig. 1).…”

Section: Newport Areamentioning

confidence: 98%

“…Our analysis is based on our geologic mapping of Siletzia over the past three decades (Wells, 1981(Wells, , 1989aWells et al, 1995Wells et al, , 2000Wells and Sawlan, 2014), building on the earlier framework by Snavely et al (1976aSnavely et al ( , 1976bSnavely et al ( , 1976cSnavely et al ( , 1993bSnavely et al ( , 1996 and Tabor and Cady (1978). Age assignments of marine strata interfi ngering and overlying the basalts of Siletzia are based on the calcareous nannoplankton (coccolith) framework, which is tied to the global biostratigraphic zonation (Bukry, 1971(Bukry, , 1973 CP-Coccolith Paleogene zones of Okada and Bukry, 1980;Bukry andSnavely, 1988, Gradstein et al, 2012).…”

Section: Approachmentioning

confidence: 98%

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Geologic history of Siletzia, a large igneous province in the Oregon and Washington Coast Range: Correlation to the geomagnetic polarity time scale and implications for a long-lived Yellowstone hotspot

et al. 2014

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Siletzia is a basaltic Paleocene and Eocene large igneous province in coastal Oregon, Washington, and southern Vancouver Island that was accreted to North America in the early Eocene. New U-Pb magmatic, detrital zircon, and 40 Ar/ 39 Ar ages constrained by detailed fi eld mapping, global nannoplankton zones, and magnetic polarities allow correlation of the volcanics with the 2012 geologic time scale. The data show that Siletzia was rapidly erupted 56-49 Ma, during the Chron 25-22 plate reorganization in the northeast Pacifi c basin. Accretion was completed between 51 and 49 Ma in Oregon, based on CP11 (CP-Coccolith Paleogene zone) coccoliths in strata overlying onlapping continental sediments. Magmatism continued in the northern Oregon Coast Range until ca. 46 Ma with the emplacement of a regional sill complex during or shortly after accretion. Isotopic signatures similar to early Columbia River basalts, the great crustal thickness of Siletzia in Oregon, rapid eruption, and timing of accretion are consistent with offshore formation as an oceanic plateau. Approximately 8 m.y. after accretion, margin parallel extension of the forearc, emplacement of regional dike swarms, and renewed magmatism of the Tillamook episode peaked at 41.6 Ma (CP zone 14a; Chron 19r). We examine the origin of Siletzia and consider the possible role of a long-lived Yellowstone hotspot using the reconstruction in GPlates, an open source plate model. In most hotspot reference frames, the Yellowstone hotspot (YHS) is on or near an inferred northeast-striking KulaFarallon and/or Resurrection-Farallon ridge between 60 and 50 Ma. In this confi guration, the YHS could have provided a 56-49 Ma source on the Farallon plate for Siletzia, which accreted to North America by 50 Ma. A sister plateau, the Eocene basalt basement of the Yakutat terrane, now in Alaska, formed contemporaneously on the adjacent Kula (or Resurrection) plate and accreted to coastal British Columbia at about the same time. Following accretion of Siletzia, the leading edge of North America overrode the YHS ca. 42 Ma. The voluminous high-Ti basaltic to alkalic magmatism of the 42-35 Ma Tillamook episode and extension in the forearc may be related to the encounter with an active YHS. Clockwise rotation of western Oregon about a pole in the backarc has since moved the Tillamook center and underlying Siletzia northward ~250 km from the probable hotspot track on North America. In the reference frames we examined, the YHS arrives in the backarc ~5 m.y. too early to match the 17 Ma magmatic fl are-up commonly attributed to the YHS. We suggest that interaction with the subducting slab may have delayed arrival of the plume beneath the backarc.

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Section: Newport Areamentioning

confidence: 98%

Section: Approachmentioning

confidence: 98%

Geologic history of Siletzia, a large igneous province in the Oregon and Washington Coast Range: Correlation to the geomagnetic polarity time scale and implications for a long-lived Yellowstone hotspot

et al. 2014

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“…The Cape Foulweather basalt of Government Point, Oregon is associated with lavas and tuff breccias which grade northward into water-laid tuff, basaltic sandstone and siltstone (Snaveley et al 1973;1976) which were sampled (192,193). Similarly two samples (194,195) of basaltic sandstone derived from erosion of the upper Eocene Yachats basalt (Snaveley & MacLeod 1974) in the central Oregon coastal area were collected.…”

Section: Mafic Sands From Volcanic Sourcesmentioning

confidence: 99%

Petrography and geochemistry of feldspathic and mafic sediments of the northeastern Pacific margin

Kamp

Leake

1985

Transactions of the Royal Society of Edinburgh: Earth Sciences

181

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This study attempts to ascertain whether the differing provenance sources and plate tectonic settings of deposition of clastic sediments and rocks can be identified by chemical means, thus opening the increased use of these rocks and their metamorphosed derivatives in plate tectonic modelling. Mineralogically immature feldspathic and mafic sands, muds, sandstones and shales from Mesozoic, Cenozoic and Holocene clastic deposits in California, Oregon, Alaska and Colorado have been both modally and chemically analysed providing a valuable data base (217 samples; 216 samples chemically analysed, many for 28 elements).There is significant upward chemical variation in the Great Valley sequence of California which mimics previously described petrographic variation and in turn reflects provenance changes with igneous episodes and erosional stripping of the Sierra Nevada in late Mesozoic time. Differing sandstone petrofacies result in varying chemical signatures and while the provenances of monomict sediments are easiest to identify, polymict sources involving granitoid or ophiolitic material can often be identified by potassium feldspar or Cr contents. The distinction of K which is derived from detrital potassium feldspar from K derived from detrital illite, micas or other sheet minerals, is best made by a Niggli al–alk plot against k. Mafic sandstones derived from mafic volcanic or plutonic rocks preserve essentially mafic igneous chemistry and could be possible parent sources of some amphibolites which grade into metasediments. The lithified erosion products of the Sierra Nevada calc-alkaline igneous rocks have higher Niggli al–alk and higher average Niggli si at any given mg value than the fresh igneous rocks enabling meta-arkoses to be distinguished from meta-igneous rocks.Applying previously published chemical criteria gives the actual plate tectonic setting of deposition of most of the sandstones studied. This suggests that the chemical composition of sandstones can yield much more information about the provenance and plate tectonic setting than hitherto recognised.

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“…The Yachats Basalt consists of seaward-dipping basalt flows about 37 m.y. old that were erupted from a west-northwestoriented dike swarm intruding the accreted Siletz terrane onshore (Snavely and MacLeod, 1974;Snavely et al, 1976;Wells et al, 2014;Wells and Blakely, 2019). Wells et al (2014) have argued that the Yachats Basalt, as well as several other middle-to-late Eocene volcanic units (Figure 1A), formed in a margin parallel extensional stress field and were subsequently rotated approximately 50 °clockwise along with the entire Oregon block of the Siletz terrane.…”

Section: Introductionmentioning

confidence: 99%

Deformation of the Juan de Fuca Plate Beneath the Central Cascadia Continental Margin (44°-45°N) in Response to an Upper Plate Load

Tréhu,

Davenport,

Kenyon

et al. 2023

Earth Sci. Syst. Soc.

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A 3D crustal model for the central Cascadia continental shelf and Coast Range between 44°N and 45°N shows that the crystalline crust of the forearc wedge beneath the coastline is characterized by a NW-trending, vertical slab of high-velocity rock interpreted to represent the dike complex that fed the Yachats Basalt, which was intruded into the forearc approximately 37 million years ago. A spatial correlation is observed between downward deflection of the crust of the subducting Juan de Fuca plate, inferred from inversion of PmP arrivals to image the Moho surface, and the high velocity (and consequently high density) anomaly underlying the Yachats Basalt. Apparent subsequent rebound of the subducting plate at greater depth suggests a primarily elastic response of the subducting plate to this load. Calculations for a range of plausible values for the magnitude of the load and the width and depth of the depression indicate that the effective elastic thickness of the subducted Juan de Fuca plate is < 6 km. Although our simple analytical models do not include partial support of the load of the slab by the adjacent upper plate crust or time dependence to account for the motion of the slab beneath the load, incorporation of those effects should decrease rather than increase the apparent strength of the subducted plate. We conclude that the subducted Juan de Fuca plate beneath the central Oregon margin is elastically thin and has the potential to store elastic strain energy before rupturing. Our model of a well-defined, focused and static upper plate load that locally deforms the subducted plate within the nominally seismogenic or transitional part of the Cascadia plate boundary may be unique in providing a relatively straightforward scenario for estimating the mechanical properties of the subducted Juan de Fuca plate. We extrapolate from these results to speculate that elastic deformation of the subducting plate may contribute to the low level of seismicity throughout much of the Cascadia forearc in the inter-seismic period between great earthquakes but note that our local results do not preclude faulting or elasto-plastic deformation of a thin and weak plate as it subducts. These results also suggest that the subducting plate should deform in response to larger scale variations in upper plate thickness and density.

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Preliminary bedrock geologic map of the Waldport and Tidewater quadrangles, Oregon

Cited by 3 publications

References 0 publications

Geologic history of Siletzia, a large igneous province in the Oregon and Washington Coast Range: Correlation to the geomagnetic polarity time scale and implications for a long-lived Yellowstone hotspot

Geologic history of Siletzia, a large igneous province in the Oregon and Washington Coast Range: Correlation to the geomagnetic polarity time scale and implications for a long-lived Yellowstone hotspot

Petrography and geochemistry of feldspathic and mafic sediments of the northeastern Pacific margin

Deformation of the Juan de Fuca Plate Beneath the Central Cascadia Continental Margin (44°-45°N) in Response to an Upper Plate Load

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