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Siletzia Terrane

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Journal Article
Journal: Geology
Published: 12 February 2025
Geology (2025) 53 (4): 380–384.
... are coeval with and have similar depositional settings as the precollisional strata of Siletzia. Our findings are consistent with the initial construction of both terranes as conjugate oceanic plateaus that formed on different sides of an Eocene spreading ridge offshore the Pacific Northwest...
FIGURES
Journal Article
Journal: Lithosphere
Publisher: GSW
Published: 17 October 2018
Lithosphere (2018) 10 (6): 792–805.
... the interval of time between accretion of the Siletzia terrane to the west and inception of the Cascade arc. The sequence dominantly consists of moderately evolved tholeiitic basalts (9.3–3.1 wt% MgO; Mg# = 0.66–0.29) and scarce rhyolites that erupted in the forearc but are chemically and isotopically similar...
FIGURES | View All (9)
Image
Generalized stratigraphy of Yakutat and Siletzia terranes from Plafker (1987) and Wells et al. (2000). Left side shows Yakutat terrane exposed in the Samovar Hills, a nunatak surrounded by the Malaspina Glacier (Alaska; photos by R. Wells). J-K acc.—Jurassic–Cretaceous accretionary. Upper left photo shows subaerial Eocene Kultieth formation unconformably overlying vertically dipping accretionary complex of Yakutat Formation. Lower left photo shows Yakutat Formation thrust over Eocene marine mudstone of Oily Creek (Cr.). Person below thrust is 2 m tall. Upper right photo shows 10-m high-cliff of fluvial Eocene Tyee Formation (with permission from Santra et al., 2013). Tyee unconformably overlies thrust separating Siletz River Volcanics from overlying Mesozoic accretionary complex of the Dothan Formation. Note that the early history of the Yakutat terrane is very similar to that of Siletzia. Lower right photo shows pillow basalt of the Siletz River Volcanics (SRV).
Published: 01 August 2014
Figure 10. Generalized stratigraphy of Yakutat and Siletzia terranes from Plafker (1987) and Wells et al. (2000) . Left side shows Yakutat terrane exposed in the Samovar Hills, a nunatak surrounded by the Malaspina Glacier (Alaska; photos by R. Wells). J-K acc.—Jurassic–Cretaceous accretionary
Journal Article
Journal: GSA Bulletin
Published: 30 June 2023
GSA Bulletin (2024) 136 (1-2): 725–740.
...) document collapse of this plateau and define a SW-younging age progression attributed to breakoff and rollback of the Farallon slab following accretion of the Siletzia terrane at ca. 50 Ma. All of the rocks have chemical traits of arc magmas, likely inherited from their lower-crustal sources, but low B...
FIGURES | View All (15)
Series: GSA Field Guide
Published: 24 September 2021
DOI: 10.1130/2021.0062(02)
EISBN: 9780813756622
... is illustrated at a quarry in the northern end of the basin where the contact between the oceanic crust of the underlying Siletzia terrane and submarine fan deposits of the Tyee Formation is exposed. The Tyee Formation provides an excellent opportunity to see the facies and three-dimensional geometry of deep...
FIGURES | View All (53)
Journal Article
Journal: GSA Bulletin
Published: 09 March 2021
GSA Bulletin (2021) 133 (11-12): 2418–2438.
... of Washington and Oregon and suggest that drainage within the Chumstick basin fed a regional river system that flowed to a forearc or marginal basin on the newly accreted Siletzia terrane. More generally, excellent age control from five interbedded tuffs and high sediment accumulation rates allow us to track...
FIGURES | View All (11)
Journal Article
Journal: GSA Bulletin
Published: 01 March 2016
GSA Bulletin (2016) 128 (3-4): 425–441.
... erosion during accretion of the Siletzia terrane between 51.3 and 49.9 Ma. Immediately following accretion, dextral strike-slip faulting began, or accelerated, on the Darrington–Devil’s Mountain, Entiat, Leavenworth, Eagle Creek, and Straight Creek–Fraser fault zones between 50 and 46 Ma. During this time...
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Journal Article
Journal: Geology
Published: 01 September 2013
Geology (2013) 41 (9): 1027–1030.
... rates and earthquake hazards. Northwest-directed Basin and Range extension of 140 km is predicted behind the southern arc since 16 Ma, and 70 km of shortening is predicted in the northern arc. The GPS rotation poles overlie a high-velocity slab of the Siletzia terrane dangling into the mantle beneath...
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Image
Synthesis of generalized block diagrams showing changes in geology and proposed sediment drainage patterns in Western Washington State during the Cenozoic. ST = Siletzia terrane; GB = Georgia Basin; SB = Swauk Basin.
Published: 06 November 2020
Figure 9 Synthesis of generalized block diagrams showing changes in geology and proposed sediment drainage patterns in Western Washington State during the Cenozoic. ST = Siletzia terrane; GB = Georgia Basin; SB = Swauk Basin.
Image
Shaded relief, digital elevation map of the Pacific Northwest (USA) showing approximate distribution of ancestral and modern Cascades arc rocks (compiled from Wagner and Saucedo, 1987; Smith, 1993; and Sherrod and Smith, 2000). Locations of principal Holocene to Pleistocene stratovolcanoes (names in italics) of the modern arc are shown for reference. Approximate outline of the Siletzia terrane is from Wells et al. (1998).
Published: 01 October 2011
stratovolcanoes (names in italics) of the modern arc are shown for reference. Approximate outline of the Siletzia terrane is from Wells et al. (1998) .
Image
Map showing the distribution of mineral deposits and occurrences associated with ancestral Cascades arc magmatism; numbered deposits correspond to those in Table 3. Dashed red line is the approximate outline of the Siletzia terrane (from Wells et al., 1998). Dashed black lines delineate areas in which multiple samples have adakitic compositions. Mineral deposits and occurrences are modified from the U.S. Geological Survey Mineral Resources Data System database (http://tin.er.usgs.gov/mrds/find-mrds.php).
Published: 01 October 2011
Figure 15. Map showing the distribution of mineral deposits and occurrences associated with ancestral Cascades arc magmatism; numbered deposits correspond to those in Table 3 . Dashed red line is the approximate outline of the Siletzia terrane (from Wells et al., 1998 ). Dashed black lines
Image
Cartoon cross section of Cascadia subduction at the latitude of central Oregon (based onDelph et al. 2018). This illustrates the oceanic Juan de Fuca plate subducting below North America. The crust is shown in grey and mantle lithosphere is indicated in green. Shallow dehydration results in serpentinization of the mantle wedge. The region of Holocene volcanism is indicated by a red bar for central Oregon, and the accreted Siletzia terrane is labeled with the eastern boundary indicated roughly by the dashed line. Surface topography (above sea level) is shown at an exaggerated scale (to the right) compared with the crust and mantle structures.
Published: 01 August 2022
results in serpentinization of the mantle wedge. The region of Holocene volcanism is indicated by a red bar for central Oregon, and the accreted Siletzia terrane is labeled with the eastern boundary indicated roughly by the dashed line. Surface topography (above sea level) is shown at an exaggerated scale
Image
Paleogeologic map computed for 60 Ma (middle Paleocene) from model NI. Colored outcrops and black fault traces were restored from the digital geologic map of Garrity and Soller (2009); colored fault traces were restored from the Bird and Ingersoll (2022) database. White areas on paleogeologic maps occur where outcrops younger than the fiducial epoch have been removed and where edges along strike-slip faults have been chiseled. A-B and C-D—western limit of exposed Cretaceous granodiorite (Kg) magmatic arc; E-F—eastern limit of exposed Cretaceous granodiorite (Kg) magmatic arc; B-C—reconstructed trace of Nacimiento sinistral fault, with inferred sinistral offset of ~370 km; C-F—continuation of the Nacimiento fault (trace Nacimiento–Caborca–Durango–Zacatecas; Caborca and Durango-Zacatecas segments); S (and surrounding heavy dashed outline)—present Siletzia terrane, which had not yet formed or accreted at this time (Wells et al., 2014); SMOc (Sierra Madre Occidental), and surrounding blue outline)— inferred zone of paleo-high μ in Sierra Madre Occidental. Restored Salinia is outlined in purple. One unexplained outlier of Kg in northern Mexico is outlined in red; outliers along the central Baja California coast are considered part of an accreted terrane. Polyconic projection is centered on meridian 110°W.
Published: 03 January 2025
—reconstructed trace of Nacimiento sinistral fault, with inferred sinistral offset of ~370 km; C-F—continuation of the Nacimiento fault (trace Nacimiento–Caborca–Durango–Zacatecas; Caborca and Durango-Zacatecas segments); S (and surrounding heavy dashed outline)—present Siletzia terrane, which had not yet formed
Image
Geologic maps showing the distribution and composition of ancestral Cascades arc rocks. Dashed red is the approximate outline of the Siletzia terrane from Wells et al. (1998). Pale blue and tan areas show the distribution of High Cascades rocks and Columbia River Basalt, respectively; these distributions are portrayed to delineate the maximum extent to which ancestral Cascades rocks might be concealed by these younger volcanic rocks. Because the ages of most small intrusive masses are unknown, each time interval shows the distribution of all intrusive rocks; the 45–36 Ma time interval map does not show the distribution of intrusive rocks because exposed intrusions older than ca. 36 Ma are rare. (A) 45–36 Ma. (B) 35–26 Ma. (C) 25–18 Ma. (D) 17–8 Ma. (E) 7–2 Ma. (F) Distribution and age of samples included in geochemical compilation (du Bray et al., 2006).
Published: 01 October 2011
Figure 3. Geologic maps showing the distribution and composition of ancestral Cascades arc rocks. Dashed red is the approximate outline of the Siletzia terrane from Wells et al. (1998) . Pale blue and tan areas show the distribution of High Cascades rocks and Columbia River Basalt, respectively
Image
Geologic maps showing the distribution and composition of ancestral Cascades arc rocks. Dashed red is the approximate outline of the Siletzia terrane from Wells et al. (1998). Pale blue and tan areas show the distribution of High Cascades rocks and Columbia River Basalt, respectively; these distributions are portrayed to delineate the maximum extent to which ancestral Cascades rocks might be concealed by these younger volcanic rocks. Because the ages of most small intrusive masses are unknown, each time interval shows the distribution of all intrusive rocks; the 45–36 Ma time interval map does not show the distribution of intrusive rocks because exposed intrusions older than ca. 36 Ma are rare. (A) 45–36 Ma. (B) 35–26 Ma. (C) 25–18 Ma. (D) 17–8 Ma. (E) 7–2 Ma. (F) Distribution and age of samples included in geochemical compilation (du Bray et al., 2006).
Published: 01 October 2011
Figure 3. Geologic maps showing the distribution and composition of ancestral Cascades arc rocks. Dashed red is the approximate outline of the Siletzia terrane from Wells et al. (1998) . Pale blue and tan areas show the distribution of High Cascades rocks and Columbia River Basalt, respectively
Image
Geologic maps showing the distribution and composition of ancestral Cascades arc rocks. Dashed red is the approximate outline of the Siletzia terrane from Wells et al. (1998). Pale blue and tan areas show the distribution of High Cascades rocks and Columbia River Basalt, respectively; these distributions are portrayed to delineate the maximum extent to which ancestral Cascades rocks might be concealed by these younger volcanic rocks. Because the ages of most small intrusive masses are unknown, each time interval shows the distribution of all intrusive rocks; the 45–36 Ma time interval map does not show the distribution of intrusive rocks because exposed intrusions older than ca. 36 Ma are rare. (A) 45–36 Ma. (B) 35–26 Ma. (C) 25–18 Ma. (D) 17–8 Ma. (E) 7–2 Ma. (F) Distribution and age of samples included in geochemical compilation (du Bray et al., 2006).
Published: 01 October 2011
Figure 3. Geologic maps showing the distribution and composition of ancestral Cascades arc rocks. Dashed red is the approximate outline of the Siletzia terrane from Wells et al. (1998) . Pale blue and tan areas show the distribution of High Cascades rocks and Columbia River Basalt, respectively
Image
Geologic maps showing the distribution and composition of ancestral Cascades arc rocks. Dashed red is the approximate outline of the Siletzia terrane from Wells et al. (1998). Pale blue and tan areas show the distribution of High Cascades rocks and Columbia River Basalt, respectively; these distributions are portrayed to delineate the maximum extent to which ancestral Cascades rocks might be concealed by these younger volcanic rocks. Because the ages of most small intrusive masses are unknown, each time interval shows the distribution of all intrusive rocks; the 45–36 Ma time interval map does not show the distribution of intrusive rocks because exposed intrusions older than ca. 36 Ma are rare. (A) 45–36 Ma. (B) 35–26 Ma. (C) 25–18 Ma. (D) 17–8 Ma. (E) 7–2 Ma. (F) Distribution and age of samples included in geochemical compilation (du Bray et al., 2006).
Published: 01 October 2011
Figure 3. Geologic maps showing the distribution and composition of ancestral Cascades arc rocks. Dashed red is the approximate outline of the Siletzia terrane from Wells et al. (1998) . Pale blue and tan areas show the distribution of High Cascades rocks and Columbia River Basalt, respectively
Image
Geologic maps showing the distribution and composition of ancestral Cascades arc rocks. Dashed red is the approximate outline of the Siletzia terrane from Wells et al. (1998). Pale blue and tan areas show the distribution of High Cascades rocks and Columbia River Basalt, respectively; these distributions are portrayed to delineate the maximum extent to which ancestral Cascades rocks might be concealed by these younger volcanic rocks. Because the ages of most small intrusive masses are unknown, each time interval shows the distribution of all intrusive rocks; the 45–36 Ma time interval map does not show the distribution of intrusive rocks because exposed intrusions older than ca. 36 Ma are rare. (A) 45–36 Ma. (B) 35–26 Ma. (C) 25–18 Ma. (D) 17–8 Ma. (E) 7–2 Ma. (F) Distribution and age of samples included in geochemical compilation (du Bray et al., 2006).
Published: 01 October 2011
Figure 3. Geologic maps showing the distribution and composition of ancestral Cascades arc rocks. Dashed red is the approximate outline of the Siletzia terrane from Wells et al. (1998) . Pale blue and tan areas show the distribution of High Cascades rocks and Columbia River Basalt, respectively
Image
Geologic maps showing the distribution and composition of ancestral Cascades arc rocks. Dashed red is the approximate outline of the Siletzia terrane from Wells et al. (1998). Pale blue and tan areas show the distribution of High Cascades rocks and Columbia River Basalt, respectively; these distributions are portrayed to delineate the maximum extent to which ancestral Cascades rocks might be concealed by these younger volcanic rocks. Because the ages of most small intrusive masses are unknown, each time interval shows the distribution of all intrusive rocks; the 45–36 Ma time interval map does not show the distribution of intrusive rocks because exposed intrusions older than ca. 36 Ma are rare. (A) 45–36 Ma. (B) 35–26 Ma. (C) 25–18 Ma. (D) 17–8 Ma. (E) 7–2 Ma. (F) Distribution and age of samples included in geochemical compilation (du Bray et al., 2006).
Published: 01 October 2011
Figure 3. Geologic maps showing the distribution and composition of ancestral Cascades arc rocks. Dashed red is the approximate outline of the Siletzia terrane from Wells et al. (1998) . Pale blue and tan areas show the distribution of High Cascades rocks and Columbia River Basalt, respectively
Image
(A) Massive mudstone and siltstone of the Aldwell Formation represents precollisional pelagic to hemipelagic basin deposits in isolated grabens on the Siletzia terrane. Interbedded sandstone in the Aldwell Formation represents turbidity currents that reached the plateau as it approached the continental margin prior to collision. Interbedded volcaniclastic conglomerate, breccia, tuff, and intermediate to felsic volcanics in the Lower Aldwell Formation support late-stage silicic volcanism during end-phases of oceanic plateau construction. (B) Collision of Siletzia resulted in an influx of coarse-grained sediment onto the accreted fragment of oceanic plateau; an angular unconformity marks this collision and separates the lower sandy member of the Lyre Formation from underlying deformed Aldwell and Crescent Formation rocks. Deformation was the result of a westward-propagating fold-and-thrust belt onto the accreted fragment of Siletzia; the lower sandy member of the Lyre Formation represents initial sheet sands and distal turbidite deposits derived from continental sources delivered to the newly formed basin on top of Siletzia. Outboard migration of the trench occurred by ca. 48 Ma, and this resulted in exhumation near the trench and deposition of Cape Flattery breccias. The accreted fragment of Siletzia was incorporated into the new subduction complex following outboard trench migration. Continued exhumation along the Lower Elwha Fault (LEF) and Boundary Creek Fault (BCF) in the subduction complex reworked precollisional units into isolated trench-slope basins as the conglomeratic upper member of the Lyre Formation. This is mixed with continued deposition of continentally derived sediments. (C) The postcollisional phase of basin deposition is marked by the Hoko River Formation. Seamount subduction results in exhumation of the frontal subduction complex and an influx of basaltic detritus from exhumed basement basalt material into isolated trench-slope basins. Most of the Hoko River Formation is characterized by distal deep-marine turbidite deposits and marks a period of regional subsidence following seamount subduction. This results in an infilling of isolated trench-slope basins and a more integrated regional basin through deposition of the Upper Hoko River Formation. (D) Continued subsidence and an influx of continentally derived sediment results in the establishment of the regional Tofino–Juan de Fuca forearc basin. Compositional and geochronologic data support a strong influence from continentally derived sources further inboard than the Western Mélange Belt (WMB), such as the Coast Mountains Batholith (CMB) and Cascades Crystalline Core (CC). Age and composition of the Makah Formation correlate to the Carmanah Group on southern Vancouver Island (VI), and further support a more integrated and regional forearc basin system at this time. Local faulting, unconformity development, and broad regional folding of the Hoko River and Makah formations indicate that regional faults likely remained active during the Oligocene. BMU—Blue Mountain Unit; CF—Crescent Fault; CFa—Cape Flattery; DZ—detrital zircon; NGW—Needles–Gray Wolf Lithic Assemblage; OSC—Olympic subduction complex.
Published: 22 November 2024
Figure 8. (A) Massive mudstone and siltstone of the Aldwell Formation represents precollisional pelagic to hemipelagic basin deposits in isolated grabens on the Siletzia terrane. Interbedded sandstone in the Aldwell Formation represents turbidity currents that reached the plateau as it approached