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Imnaha Basalt

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Series: GSA Special Papers
Published: 01 January 1989
DOI: 10.1130/SPE239-p105
... The K-Ar data for various sections of the Columbia River basalt (Imnaha, Picture Gorge, and Grande Ronde Basalt formations) have been reevaluated, utilizing the atmospheric argon contents of the rocks to identify the least altered samples. These ages, together with the results of paleomagnetic...
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Isopach map) of the Imnaha Basalt, the basal section of the CRBG. A thick section of the Imnaha Basalt is oriented subparallel to the modern Hells Canyon: this increased thickness requires the presence of a Miocene proto-Hells Canyon. The modern Hells Canyon is coincident with the proto-Hells Canyon in one portion of the modern Hells Canyon by Pittsburg Landing. This is interpreted to be a proto-Hells Canyon. Most of the modern southern Hells Canyon, such as by Hells Canyon Dam, does not coincide with the proto-Hells Canyon.
Published: 01 July 2020
Figure 4. Isopach map) of the Imnaha Basalt, the basal section of the CRBG. A thick section of the Imnaha Basalt is oriented subparallel to the modern Hells Canyon: this increased thickness requires the presence of a Miocene proto-Hells Canyon. The modern Hells Canyon is coincident with the proto
Published: 01 August 2013
DOI: 10.1130/2013.2497(11)
... We present a reappraisal of Columbia River basalt petrogenesis based on an internally consistent X-ray fluorescence and inductively coupled plasma–mass spectrometry data set for major and trace elements plus new and existing isotopic analyses of the Imnaha, Steens, Picture Gorge, and Grande...
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Published: 01 June 2008
TABLE 1. ISOTOPE ANALYSES OF STEENS AND IMNAHA BASALTS*
Journal Article
Journal: GSA Bulletin
Published: 07 March 2025
GSA Bulletin (2025)
... Stage II (ca. 16.6−15.9 Ma), when fissure eruptions began along the Chief Joseph dike swarm to generate Imnaha, Grande Ronde, and Wanapum Basalts. Imnaha Basalt is the product of fractional crystallization of an underplated primary magma derived from melting of a channelized plume source that was least...
Journal Article
Journal: GSA Bulletin
Published: 01 February 1976
GSA Bulletin (1976) 87 (2): 215–225.
...GREGORY S. HOLDEN; PETER R. HOOPER Abstract Field characteristics, petrography, and major-element analyses are given for 17 of the 19 flows of the Columbia River Group present in a canyon in the southeast corner of the Columbia Plateau. The 17 flows are divided into 4 flows of Imnaha Basalt...
Journal Article
Published: 01 July 2020
Rocky Mountain Geology (2020) 55 (1): 27–54.
...Figure 4. Isopach map) of the Imnaha Basalt, the basal section of the CRBG. A thick section of the Imnaha Basalt is oriented subparallel to the modern Hells Canyon: this increased thickness requires the presence of a Miocene proto-Hells Canyon. The modern Hells Canyon is coincident with the proto...
FIGURES | View All (9)
Published: 01 August 2013
DOI: 10.1130/2013.2497(09)
.../ 86 Sr ratios of <0.7040. In contrast, Imnaha, Grande Ronde, Wanapum, and Saddle Mountains basalts likely assimilated crust with more radiogenic Sr (>0.7040) including a cratonic component, perhaps as a result of residence in magma chambers partly located east of the 87 Sr/ 86 Sr = 0.7060 line...
Published: 01 August 2013
DOI: 10.1130/2013.2497(03)
... with the plagioclase ages. Various forms of the geomagnetic polarity time scale for mid-Miocene time are examined, along with the ages of lavas and their magnetic polarity. The main sections of the Columbia River Basalt Group (Imnaha through Wanapum Basalt) were formed in ~0.5 m.y. between 16.3 and 15.8 Ma. Steens...
Journal Article
Journal: GSA Bulletin
Published: 01 May 1976
GSA Bulletin (1976) 87 (5): 777–792.
... ratios (0.7035 to 0.7039) and a major- and trace-element composition consistent with an origin from the upper mantle. The Picture Gorge Basalt is clearly distinguished from the Imnaha basalt in northeast Oregon and from the widespread, mainly younger Yakima Basalt. The Yakima Basalt, including lava flows...
Journal Article
Journal: Geosphere
Published: 01 June 2008
Geosphere (2008) 4 (3): 480–495.
...TABLE 1. ISOTOPE ANALYSES OF STEENS AND IMNAHA BASALTS* ...
FIGURES | View All (10)
Journal Article
Journal: Geology
Published: 31 January 2020
Geology (2020) 48 (4): 348–352.
... with the strongest arc-like (but depleted) geochemical signal of PGB among CRBG units indicates that the shallowest metasomatized backarc-like mantle was tapped first and concurrently, with later units (Steens and Imnaha Basalts) showing increased influence of a plume-like source. * E-mails: [email protected]...
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Journal Article
Journal: Geosphere
Published: 26 September 2018
Geosphere (2018) 14 (6): 2505–2532.
...-rock and mineral compositions, which we use to evaluate how the balance of magma differentiation processes change in time. Temporal petrochemical variations in the Steens Basalt are analogous to the transition from Imnaha Basalt to Grande Ronde Basalt units of the Columbia River Flood Basalt and have...
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Published: 01 August 2013
DOI: 10.1130/2013.2497(02)
... that compose the lava stratigraphy. Combining robust Ar-Ar data with field constraints and paleomagnetic information leads to the following recommendations for the age of emplacement of the constituent formations: Steens Basalt, ca. 16.9 to ca. 16.6 Ma; Imnaha Basalt, ca. 16.7 to ca. 16 Ma; Grande Ronde Basalt...
Published: 01 August 2013
DOI: 10.1130/2013.2497(05)
... in the interior and an abbreviated and variable stratigraphy along the margins. The areal extent of many flows suggests that the Chief Joseph dike swarm greatly expanded after Imnaha Basalt time, and now many dikes are buried beneath younger flows in the eastern part of the province. The Grande Ronde Basalt has...
Series: GSA Special Papers
Published: 01 January 1989
DOI: 10.1130/SPE239-p321
... percent; K 2 O, 6 percent; and TiO 2 , 0.7 percent. The modal abundance by volume varies from a trace in the Picture Gorge Basalt and 1 percent in some Imnaha Basalt flows to 10 percent in the Grande Ronde Basalt and as much as 24 percent in the Wanapum Basalt. If segregated and accumulated, this glass...
Journal Article
Journal: GSA Bulletin
Published: 01 January 2004
GSA Bulletin (2004) 116 (1-2): 249–250.
... Mountain and Malheur Gorge is petrographically unusual in that it contains significantly more and larger phenocrysts than the overlying Imnaha Basalt. The reversed-to-normal magnetic break recorded by Taubeneck at the base of the Imnaha Basalt along the southern margin of the Wallowa Mountains ( Carlson...
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Geochemistry of our Picture Gorge Basalt (PGB, northwestern United States) study samples compared to the Steens Basalt data from Moore et al. (2018) (*) and all main-phase Columbia River Basalt Group (CRBG) units from Wolff and Ramos (2013) (**). For the Imnaha Basalt, only the American Bar subgroup samples are plotted, as only these Imnaha lavas occur in the study area of northeastern Oregon (Vic Camp, 2019, personal commun.). Dated sample locations are abbreviated as in Figure 1.
Published: 31 January 2020
Figure 2. Geochemistry of our Picture Gorge Basalt (PGB, northwestern United States) study samples compared to the Steens Basalt data from Moore et al. (2018) (*) and all main-phase Columbia River Basalt Group (CRBG) units from Wolff and Ramos (2013) (**). For the Imnaha Basalt, only
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Figure 5. Stratigraphy and map distribution of main Columbia River Basalt Group (CRBG) units. (A) Stratigraphy and source components of the Columbia River Basalt Group units that erupted along cross-section A–A′ in Figure 1. Letters (a)–(d) correspond with the evolution of each formation as depicted in the cross-sectional diagrams of Figure 7. Paleo-magnetic units R0–N2 correspond with sequential reverse and normal paleomagnetic intervals during the main-phase eruptions. The terms lower Steens and upper Steens Basalts are defined in Hooper et al. (2002) and Camp et al. (2003). Imnaha Basalt clearly overlies lower Steens Basalt in the Malheur Gorge of eastern Oregon (Hooper et al., 2002). The stratigraphic relationship between Imnaha Basalt and upper Steens Basalt is poorly constrained, although they may be interbedded with one another south of the Malheur Gorge region (Camp et al., 2003). (B) Map distribution of main Columbia River Basalt Group units. Northward migration of volcanism is evident in the northward offlap of progressively younger units from southeastern Oregon into northeastern Oregon and adjacent Washington State.
Published: 01 June 2008
as depicted in the cross-sectional diagrams of Figure 7 . Paleo-magnetic units R0–N2 correspond with sequential reverse and normal paleomagnetic intervals during the main-phase eruptions. The terms lower Steens and upper Steens Basalts are defined in Hooper et al. (2002) and Camp et al. (2003) . Imnaha
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Temporal evolution of whole rock Mg#, Ba/Ta, and (La/Sm)N for the Columbia River Basalt Group (CRBG), Deccan Traps, and Siberian Traps. Black bars represent the full range of values from each formation or subgroup; white circles represent the mean of each data range. Gray shaded regions highlight sections of each continental flood basalt (CFB) where a mafic, recharge phase is evident. The individual CFB are ordered from most voluminous at the top (Siberian Traps), to least voluminous at the bottom (Steens Basalt). Formations are ordered stratigraphically within each CFB; the dashed gray line at the base of the Imnaha Basalt denotes a transition to the northward section of the CRBG. Blue arrows indicate a shift to a mafic compositional range within CFB (similar to the lower A-lower B Steens transition), whereas red arrows highlight a shift to more evolved compositional ranges (similar to the lower B-upper Steens transition). Imnaha Basalt, Grande Ronde Basalt, Deccan Traps, and Siberian Traps data from GeoRoc precompiled files (accessed June 2016 and January 2017). Mg#—100*[Mg/(Mg+FeT)].
Published: 26 September 2018
; the dashed gray line at the base of the Imnaha Basalt denotes a transition to the northward section of the CRBG. Blue arrows indicate a shift to a mafic compositional range within CFB (similar to the lower A-lower B Steens transition), whereas red arrows highlight a shift to more evolved compositional ranges