The analytical equipment used to determine the abundances of isotopes is more accurate in determining ratios of isotopes than their absolute abundances.
Therefore, Sr as the y-axis would allow the isotope ratios of all rocks in a lava flow to be plotted. Damon, "K-Ar Age of Lava Dam in the Grand Canyon," Geological Society of America Bulletin, 79 (Jan.
A probable cause of the fictitious isochron ages of Grand Canyon lava flows will be offered in a future Impact article.
A critique of the Cardenas Lavas isochron will be included.
Fictitious Rb-Sr isochron for the Western Grand Canyon lava flows.
AJthough the lavas flowed over the rim and into the Grand Canyon, the "isochron" age of 1500 million years would make these youngest lava flows among the oldest rocks yet dated in the Grand Canyon.
Isochron confidence is well founded, for the assumptions of the dating method appear to be internally verified.
The correlation of these six points to the 1500-million-year isochron is almost as good as the six points forming the 1090-million-year isochron for the Cardenas Lavas (Figure 1), which overturned five K-Ar "model dates." Geologists, however, must reject the alleged "isochron" for the Western Grand Canyon lava flows (Figure 2) because these most recent flows would otherwise appear to be the oldest rocks of the Grand Canyon.
No geologist could accept the erosional form of the Grand Canyon as enduring for 1.5 billion years!
Popular Dating Methods Both the K-Ar and Rb-Sr methods make use of radioactive decay of a parent isotope to a stable daughter isotope. Leeman, "Late Cenozoic Alkali-Rich Basalt from the Western Grand Canyon Area, Utah and Arizona: Isotopic Composition of Strontium," Geological Society of America Bulletin, 85 (Nov. Six analyses of Uinkaret Plateau basalts (U-33, U-35, U-59, U-24, U-43, U-58) were used.
Potassium-40 (Rb has occurred since the rock cooled from the lava flow.