Tholeiitic and alkalic basalts of the Eocene Siletz River Volcanics, Oregon Coast Range

Snavely, Parke Detweiler; MacLeod, N.S.; Wagner, Holly Clyde

doi:10.2475/ajs.266.6.454

Cited by 102 publications

(57 citation statements)

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“…The pillow basalt forms large sheet fl ows and feeder tubes (Fig. 5), similar to the upper part of the SRV in Oregon ( Snavely et al, 1968). Locally the pillow basalt is overlain by porphyritic, subaerial columnar and blocky jointed basalt fl ows, vesicular submarine basalt lapilli breccias, and fringing fossiliferous shallow-water basaltic sandstones characteristic of an oceanic island environment (Wells, 1981;Wells and Sawlan, 2014).…”

Section: Willapa Hillsmentioning

confidence: 94%

“…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%

“…The bulk of the unit consists of submarine tholeiitic pillow basalt, pillow breccia, lapilli breccia, and thin deep-water mudstone interbeds exposed in broad northeast-striking anticlinoria. Although the base of the sequence near Corvallis consists of pillow basalt with mid-oceanic ridge basalt (MORB) affi nity, most of the lower tholeiitic unit has higher TiO 2 (2.5%-2.9%) typical of ocean island lavas (Snavely et al, 1968). At Ball Mountain, 30 km north of Newport, the sub marine fl ows are capped by subaerial tholeiitic and alkali basalt.…”

Section: Newport Areamentioning

confidence: 99%

“…These volcanic complexes include the Siletz River Volcanics (SRV) of Oregon, the Crescent Formation of Washington, and the Metchosin igneous complex of southern Vancouver Island. They are composed dominantly of tholeiitic and alkalic submarine and subaerial basalt, with attendant intrusive rocks, submarine breccias, marine sediments, and rare silicic fl ows that formed islands and seamounts built on ocean crust (Snavely et al, 1968). Together, they compose a large oceanic terrane that was accreted to North America in the Eocene (Snavely and MacLeod, 1974;Simpson and Cox, 1977;Duncan, 1982;Heller and Ryberg, 1983;Wells et al, 1984;McCrory and Wilson, 2013).…”

Section: Introductionmentioning

confidence: 96%

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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: Willapa Hillsmentioning

confidence: 94%

Section: Newport Areamentioning

confidence: 98%

Section: Newport Areamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

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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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“…Detailed studies of samples from the Juan de Fuca Ridge (Kay et al, 1970); Siletz River Volcanics (Snavely et al, 1968); Carnegie and Cocos ridge sites of DSDP Leg 16 (Yeats et al, 1973); and elsewhere indicate that the basaltic host rocks have close similarities in texture, mineralogy, and chemistry. Although the basalts are predominantly tholeiites, samples from Leg 34 may have affinities to alkali olivine basalts according to Hart et al (1974).…”

Section: Host Rocks and Occurrence Of Pyritementioning

confidence: 99%

Sulfur Isotope Reconnaissance of Epigenetic Pyrite in Ocean-floor Basalts, Leg 34 and Elsewhere

Field¹,

Dymond²,

Heath³

et al. 1976

Initial Reports of the Deep Sea Drilling Project

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Sulfur isotope analyses of 10 epigenetic occurrences of pyrite in ocean-floor basalts yield an unexpectedly large range of á 34 S values (from -24.2 to +23.O°/oo) for sulfides that are inferred to be of hydrothermal origin. The existing geologic, mineralogical, and isotopic data do not permit an unambiguous interpretation of the chemical and thermal characteristics of these hydrothermal systems. They fit either of two hypothetical models that assume isotopic equilibration between varying proportions of oxidized and reduced species of sulfur, but with pyrite deposition either (1) at 150°C and less from an infinite reservoir of heavy (+21°/oo) seawater sulfur, or (2) at 300°C and less from a finite reservoir of deep-seated (O°/oo) "magmatic" sulfur. Further detail and elaboration of these or alternative models must await additional mineralogical and isotopic studies, particularly of coexisting hydrothermal assemblages.

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Chemical Characteristics and Origin of Oceanic Ridge Volcanic Rocks

Kay¹,

Hubbard²,

Gast³

1972

Collected Reprint Series

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Tholeiitic and alkalic basalts of the Eocene Siletz River Volcanics, Oregon Coast Range

Cited by 102 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

Sulfur Isotope Reconnaissance of Epigenetic Pyrite in Ocean-floor Basalts, Leg 34 and Elsewhere

Chemical Characteristics and Origin of Oceanic Ridge Volcanic Rocks

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