Footprints in the news again. Helen's dacite, the calcium-rich plagioclases may have formed thousands or even a few million years ago.
As mentioned above, we already know that Austin's application of the K-Ar method to this dacite sample was flawed from the beginning. This is the logical fallacy of composition Copi and Cohen, They then proceed to assault the validity of the K-Ar method.
For even the best mineralogists and petrologists, xenocrysts may be difficult to distinguish from phenocrysts for example, Hyndman, , p. Obviously, Swenson, like many YECs, fails to realize that scientists can successfully unravel past events without witnessing them. Helens dacite, many scientists have been able to isolate specific minerals from older volcanics and successfully date them.
That is, the various minerals phenocrysts in the dacite may have grown in the parent melt at different times and the entire crystallization process may have taken as much as a few million years. Search our quick list of the eruption of late pleistocene loess from the fan perspective.
Nevertheless, as discussed in Dalrymple , p. This sample also had recognizable hornblende, evidently not completely isolated by magnetic separation.
Although Austin and Swenson will not admit it, some of the grains in Figure 4 may be xenocrysts rather than phenocrysts. Once temperatures further decline, more sodium-rich plagioclase begins to solidify from the melt and may surround the calcium-rich grains. I'm skeptical that the defects and fractures in the orthopyroxenes and feldspars of Austin's dacites could hold more excess argon per mineral volume than the relatively large open structures within the hornblendes Dickin, , p. Search our quick list of the eruption of late pleistocene loess from the fan perspective.
Posted by: Taukinos | on October 2, 2012
They said that Dr Austin should have known they were old because the crystals were large and zoned. Stars before earth 4.
Instead, the relatively low mass of the Earth and its relatively close proximity to the Sun has resulted in silicon, potassium, iron and other less volatile elements concentrating in it. History; 5 gallery; this study of catastrophe.
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