Petrology of late Eocene lavas erupted in the forearc of central Oregon

Davis, Alicé S.; Snavely, Parke Detweiler; Gray, Leda-Beth; Minasian, D.L.

doi:10.3133/ofr9540

Cited by 6 publications

(11 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Major element and trace element chemistry by Snavely and MacLeod (1974), Phillips et al (1989); Barnes and Barnes (1992), Davis et al (1995) Parker et al (2010, and Chan et al (2012) characterized the fl ows as enriched (E) MORB and ocean island basalt (OIB) lavas. Parker et al (2010) and Chan et al (2012) suggested that the Yachats, Cascade Head and Grays River volcanics may have been sourced in the asthenosphere beneath the Farallon plate, possibly from a plume or slab window source.…”

Section: Tillamook Magmatic Episodementioning

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

View full text Add to dashboard Cite

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.

show abstract

Section: Tillamook Magmatic Episodementioning

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

View full text Add to dashboard Cite

show abstract

“…The Oregon Coast Range is dominated by the Tyee Formation, made up primarily of turbidites deposited during the Eocene (Heller et al, 1987). In addition to these sedimentary units, our selected landscape also contains the Yachats Basalt, which erupted mostly as sub-areal flows between 3 and 9 m in thickness during the late Eocene (Davis et al, 1995). Erosion rates inferred from 10 Be concentrations in stream sediments are between 0.11 to 0.14 mm yr −1 (Heimsath et al, 2001;Bierman et al, 2001), similar to rock uplift rates of 0.05-0.35 mm yr −1 inferred from marine terraces (Kelsey et al, 1994).…”

Section: An Example Of Lithologic Variabilitymentioning

confidence: 99%

How concave are river channels?

et al. 2018

View full text Add to dashboard Cite

Abstract. For over a century, geomorphologists have attempted to unravel information about landscape evolution, and processes that drive it, using river profiles. Many studies have combined new topographic datasets with theoretical models of channel incision to infer erosion rates, identify rock types with different resistance to erosion, and detect potential regions of tectonic activity. The most common metric used to analyse river profile geometry is channel steepness, or k s . However, the calculation of channel steepness requires the normalisation of channel gradient by drainage area. This normalisation requires a power law exponent that is referred to as the channel concavity index. Despite the concavity index being crucial in determining channel steepness, it is challenging to constrain. In this contribution, we compare both slope-area methods for calculating the concavity index and methods based on integrating drainage area along the length of the channel, using so-called "chi" (χ) analysis. We present a new χ-based method which directly compares χ values of tributary nodes to those on the main stem; this method allows us to constrain the concavity index in transient landscapes without assuming a linear relationship between χ and elevation. Patterns of the concavity index have been linked to the ratio of the area and slope exponents of the stream power incision model (m/n); we therefore construct simple numerical models obeying detachment-limited stream power and test the different methods against simulations with imposed m and n. We find that χ-based methods are better than slope-area methods at reproducing imposed m/n ratios when our numerical landscapes are subject to either transient uplift or spatially varying uplift and fluvial erodibility. We also test our methods on several real landscapes, including sites with both lithological and structural heterogeneity, to provide examples of the methods' performance and limitations. These methods are made available in a new software package so that other workers can explore how the concavity index varies across diverse landscapes, with the aim to improve our understanding of the physics behind bedrock channel incision.

show abstract

“…Magmas produced in this setting are generally small in volume but diverse in composition, ranging from basalts with mid-ocean-ridge (MORB) or ocean-island (OIB) traits (Kimura et al, 2005) to adakites (Benoit et al, 2002), boninites and high-Mg andesites (Deschamps and Lallemand, 2003), and a variety of felsic rocks (Madsen et al, 2006). Mechanisms proposed to account for forearc magmatism are also diverse, the most common being subduction of a spreading ridge (Madsen et al, 2006), rifting of the overriding plate (Davis et al, 1995), breakoff of the downgoing plate (Schoonmaker et al, 2005), magma leakage along transform faults (Gill, 1981), and the presence of a mantle plume (MacPherson and Hall, 2001). Because forearc igneous rocks record events and processes operating at the entryway to a subduction zone, they are particularly useful for understanding subduction processes as well as for reconstructing plate motions and geometries.…”

Section: Introductionmentioning

confidence: 98%

“…46-32 Ma dominantly basaltic volcanism in the Oregon and southern Washington Coast Ranges. Units included in the latter are, from south to north, the Yachats Basalt and the Basalt of Cascade Head (Davis et al, 1995;Parker et al, 2010), various small alkalic intrusions (Oxford, 2006), the Tillamook volcanics (Magill et al, 1981), the Goble volcanics (Beck and Burr, 1979), and the Grays River volcanics, which are the subject of this paper . The majority of these mafi c eruptive centers were subaerial, and they subdivided the forearc basin into smaller marginal basins that subsequently fi lled with slope mudstones and turbidite sandstones (Niem et al, 1992b;Moothart , 1992).…”

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

Petrology of late Eocene lavas erupted in the forearc of central Oregon

Cited by 6 publications

References 18 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

How concave are river channels?

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

Contact Info

Product

Resources

About