Comparison of Conventional K–Ar and 40Ar/39Ar Dating of Young Mafic Volcanic Rocks

2000 ◽  
Vol 53 (3) ◽  
pp. 294-301 ◽  
Author(s):  
Marvin A. Lanphere
Keyword(s):  
Crater Lake ◽  
Volcanic Rocks ◽  
Snake River Plain ◽  
High Quality ◽  
Modern Equipment ◽  
Suitable Material ◽  
Mount Adams ◽  
River Plain ◽  
Isotope Correlation ◽  
Better Than

AbstractK–Ar and 40Ar/39Ar ages have been measured on nine mafic volcanic rocks younger than 1 myr from the Snake River Plain (Idaho), Mount Adams (Washington), and Crater Lake (Oregon). The K–Ar ages were calculated from Ar measurements made by isotope dilution and K2O measurements by flame photometry. The 40Ar/39Ar ages are incremental-heating experiments using a low-blank resistance-heated furnace. The results indicate that high-quality ages can be measured on young, mafic volcanic rocks using either the K–Ar or the 40Ar/39Ar technique. The precision of an 40Ar/39Ar plateau age generally is better than the precision of a K–Ar age because the plateau age is calculated by pooling the ages of several gas increments. The precision of a plateau age generally is better than the precision of an isotope correlation (isochron) age for the same sample. For one sample the intercept of the isochron yielded an 40Ar/36Ar value significantly different from the atmospheric value of 295.5. Recalculation of increment ages using the isochron intercept for the composition of nonradiogenic Ar in the sample resulted in much better agreement of ages for this sample. The results of this study also indicate that, given suitable material and modern equipment, precise K–Ar and 40Ar/39Ar ages can be measured on volcanic rocks as young as the latest Pleistocene, and perhaps even the Holocene.

Regionally continuous Miocene rhyolites beneath the eastern Snake River Plain reveal localized flexure at its western margin: Idaho National Laboratory and vicinity

2020 ◽  
Vol 57 (3) ◽  
pp. 241-270
Author(s):  
Kyle L. Schusler ◽  
David M. Pearson ◽  
Michael McCurry ◽  
Roy C. Bartholomay ◽  
Mark H. Anders
Keyword(s):  
Volcanic Rocks ◽  
Snake River Plain ◽  
North American Plate ◽  
Snake River ◽  
Trace Element Geochemistry ◽  
Deep Borehole ◽  
Age Progression ◽  
Western Margin ◽  
Silicic Volcanic ◽  
River Plain

The eastern Snake River Plain (ESRP) is a northeast-trending topographic basin interpreted to be the result of the time-transgressive track of the North American plate above the Yellowstone hotspot. The track is defined by the age progression of silicic volcanic rocks exposed along the margins of the ESRP. However, the bulk of these silicic rocks are buried under 1 to 3 kilometers of younger basalts. Here, silicic volcanic rocks recovered from boreholes that penetrate below the basalts, including INEL-1, WO-2 and new deep borehole USGS-142, are correlated with one another and to surface exposures to assess various models for ESRP subsidence. These correlations are established on U/Pb zircon and 40Ar/39Ar sanidine age determinations, phenocryst assemblages, major and trace element geochemistry, δ18O isotopic data from selected phenocrysts, and initial εHf values of zircon. These data suggest a correlation of: (1) the newly documented 8.1 ± 0.2 Ma rhyolite of Butte Quarry (sample 17KS03), exposed near Arco, Idaho to the upper-most Picabo volcanic field rhyolites found in borehole INEL-1; (2) the 6.73 ± 0.02 Ma East Arco Hills rhyolite (sample 16KS02) to the Blacktail Creek Tuff, which was also encountered at the bottom of borehole WO-2; and (3) the 6.42 ± 0.07 Ma rhyolite of borehole USGS-142 to the Walcott Tuff B encountered in deep borehole WO-2. These results show that rhyolites found along the western margin of the ESRP dip ~20º south-southeast toward the basin axis, and then gradually tilt less steeply in the subsurface as the axis is approached. This subsurface pattern of tilting is consistent with a previously proposed crustal flexural model of subsidence based only on surface exposures, but is inconsistent with subsidence models that require accommodation of ESRP subsidence on either a major normal fault or strike-slip fault.

Seismic imaging through the volcanic rocks of the Snake River Plain: insights from Project Hotspot

2015 ◽  
Vol 63 (4) ◽  
pp. 919-936 ◽  
Author(s):  
Lee M. Liberty ◽  
Douglas R. Schmitt ◽  
John W. Shervais
Keyword(s):  
Seismic Imaging ◽  
Volcanic Rocks ◽  
Snake River Plain ◽  
Snake River ◽  
River Plain

Seismic wave attenuation in volcanic rocks from VSP experiments

Geophysics ◽  
1991 ◽  
Vol 56 (9) ◽  
pp. 1441-1455 ◽  
Author(s):  
J. Pujol ◽  
S. Smithson
Keyword(s):  
Wave Attenuation ◽  
Volcanic Rocks ◽  
Peak Frequency ◽  
Snake River Plain ◽  
Snake River ◽  
Attenuation Coefficients ◽  
Columbia Plateau ◽  
Air Gun ◽  
The Time Domain ◽  
River Plain

Seismic wave attenuation in the Columbia Plateau basalts and Snake River Plain volcanics was analyzed using vertical seismic profiling (VSP) data. The computation of attenuation coefficients is based on fitting a straight line to the logarithm of amplitude ratios computed for fixed values of frequency and variable depth. This approach does not require any assumptions on the dependence of Q on frequency. For the Columbia Plateau basalts, the attenuation coefficients obtained from the field data are smaller than those computed from the synthetic VSP generated using the sonic and density logs, indicating that the observed attenuation is related to scattering effects and is substantially larger than the intrinsic attenuation of basalt. Therefore, it is concluded that only a lower bound for Q can be established, in agreement with recent findings by other authors. The effective attenuation of seismic energy in basalts (about [Formula: see text] for the peak frequency) is comparable to the effective attenuation observed in sedimentary rocks (between [Formula: see text] and [Formula: see text]). Results from two VSPs recorded in the Snake River Plain volcanics using air gun and vibrator sources show some frequency‐dependent effects. The depth range analyzed covers two different lithologic units (rhyolitic rocks with interbedded volcanic sediments above more homogeneous rhyodacitic rocks). The air gun energy (with a peak frequency near 15 Hz) clearly detects a difference in the attenuating properties of the two types of rocks. The vibrator energy, on the other hand, also detects this difference, but only for the lower frequencies. For frequencies near the peak frequency (31 Hz), attenuation is almost the same in the two units. The difference in attenuation for the two types of rocks is real and cannot be explained as processing artifacts, because it can be observed for both sources by analyzing the amplitude decay in the time domain. The peak‐frequency attenuation coefficients for the lower section are [Formula: see text] and [Formula: see text] for the vibrator and air gun sources, respectively. For the upper section, the corresponding values are [Formula: see text] and [Formula: see text]. The difference in attenuation implied by the last two coefficients is probably not real, because the decay of energy in the time domain for the two sources is much closer to each other. The Columbia Plateau and Snake River Plain VSPs show that the poor quality of reflection data commonly associated with volcanic rocks cannot be explained by unusually high attenuation.

K-Ar dating, Quaternary and Neogene volcanic rocks of the Snake River Plain, Idaho

1975 ◽  
Vol 275 (3) ◽  
pp. 225-251 ◽  
Author(s):  
R. L. Armstrong ◽  
W. P. Leeman ◽  
H. E. Malde
Keyword(s):  
Volcanic Rocks ◽  
Snake River Plain ◽  
Snake River ◽  
River Plain

Geochemical and isotopic evidence for the origin of continental flood basalts with particular reference to the Snake River Plain Idaho, U. S. A

1984 ◽  
Vol 310 (1514) ◽  
pp. 643-660 ◽  
Keyword(s):  
Volcanic Rocks ◽  
Snake River Plain ◽  
Snake River ◽  
Spinel Lherzolite ◽  
Magma Chambers ◽  
Flood Basalts ◽  
Continental Flood Basalts ◽  
Source Regions ◽  
River Plain ◽  
Crustal Magma

Voluminous outpourings of olivine and quartz tholeiite cover vast tracts of the western U.S.A, around the Columbia and Snake Rivers. Voluminous eruptive units within each province are petrographically and chemically homogeneous and generally lack significant lateral or temporal variation. These features suggest relatively homogeneous source regions. A possible scenario for the Snake River Plain involves extraction of tholeiitic melts from enriched spinel lherzolite mantle ( 87 Sr/ 86 Sr > 0.7058, 143 N d/ 144 Nd < 0.51252) which contains at least a component of 2.5 Ga material. Subsequent fractionation of olivine, plagioclase, apatite and magnetite in crustal magma chambers and simultaneous assimilation of crust ( ca . 20%) accounts for the isotopic variability in the more evolved ferrolatites and ferrobasalts. Unlike the olivine tholeiites these evolved volcanic rocks exhibit all the classic elemental and isotopic correlations consistent with an origin involving combined assimilation and fractional crystallization.

scholarly journals Retrieving magma composition from TIR spectra: implications for terrestrial planets investigations

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Alessandro Pisello ◽  
Francesco P. Vetere ◽  
Matteo Bisolfati ◽  
Alessandro Maturilli ◽  
Daniele Morgavi ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Degree Of Polymerization ◽  
Snake River Plain ◽  
Reflectance Spectra ◽  
Snake River ◽  
Terrestrial Planets ◽  
Vulcano Island ◽  
End Members ◽  
River Plain

Abstract Emissivity and reflectance spectra have been investigated on two series of silicate glasses, having compositions belonging to alkaline and subalkaline series, covering the most common terrestrial igneous rocks. Glasses were synthesized starting from natural end-members outcropping at Vulcano Island (Aeolian Islands, Italy) and on Snake River Plain (USA). Results show that the shift of the spectra, by taking Christiansen feature (CF) as a reference point, is correlated with SiO2 content, the SCFM factor and/or the degree of polymerization state via the NBO/T and temperature. The more evolved is the composition, the more polymerized the structure, the shorter the wavelength at which CF is observable. CF shift is also dependent on temperature. The shape of the spectra discriminates alkaline character, and it is related to the evolution of Qn structural units. Vulcano alkaline series show larger amount of Q4 and Q3 species even for mafic samples compared to the subalkaline Snake River Plain series. Our results provide new and robust insights for the geochemical characterization of volcanic rocks by remote sensing, with the outlook to infer origin of magmas both on Earth as well as on terrestrial planets or rocky bodies, from emissivity and reflectance spectra.

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