Potassium argon dating is only done with
Again, the mineral textures, as well as the laws of chemistry and physics, dictate that the calcium-rich plagioclase cores grew at higher temperatures before the sodium-rich rims and that glasses only formed once the melt erupted at the surface.
'The 'heavy-magnetic concentrate' also had glassy particles (more abundant than in the 'heavy-nonmagnetic concentrate'). De Paolo, 1985, 'Radiometric Time Scale for the Upper Eocene and Oligocene Based on K/Ar and Rb/Sr Dating of Volcanic Biotites from the Pelagic Sequence of Gubbio, Italy', Geology, v.
On the basis of the glass and mineral textures and elementary melt chemistry, we know that the zoned plagioclases and other relatively large and well-developed minerals in Austin's dacite must have taken more time to grow than the surrounding glass matrix.
By using high-temperature ovens in undergraduate university laboratories or even crystal-growing kits and kitchen chemicals, a normally intelligent person can verify that coarse crystals take more time to grow than finer-grained materials. Farrar, 1996, '40Ar/39Ar Phlogopite and U-Pb Perovskite Dating of Lamprophyre Dykes from the Eastern Lake Superior Region: Evidence for a 1.14 Ga Magmatic Precursor to Midcontinent Rift Volcanism', Can.
Clearly, basic crystal chemistry and physics dictates that zoned and other relatively large phenocrysts grew deep within the Earth and existed before the glass matrix that rapidly formed during the 1986 eruption.
'(e.g., Harland et al., 1990; Hilgen et al., 1997, p. 121-122; Baadsgaard et al., 1988; Baadsgaard et al., 1993; Queen et al., 1996; Montanari et al., 1985; and Hirschmann et al., 1997; also see Austin clearly ignores the possibility of contamination in the mass spectrometer (hypothesis #2) and the possibility that the phenocrysts in his samples may be much older than the 1986 AD eruption (hypothesis #3).
This sample also had recognizable hornblende, evidently not completely isolated by magnetic separation.' 'The 'pyroxene concentrate' (DOME-IP) was dominated by orthopyroxene and much less clinopyroxene.
Because it was composed of finer particles (170-270 mesh), it contained far fewer mafic particles with attached glass fragments than DOME-IH.
No attempt was made to separate the hornblende from the Fe-Ti oxides, but further finer milling and use of heavy liquids should be considered.''The 'heavy-nonmagnetic concentrate' (DOME-1H) was dominated by orthopyroxene with much less clinopyroxene, but had a significant quantity of glassy particles attached to mafic microphenocrysts and fragments of mafic phenocrysts along incompletely fractured grain boundaries.
These mafic microphenocrysts and fragments of mafic phenocrysts evidently increased the density of the attached glass particles above the critical density of 2.85 g/cc, which allowed them to sink in the heavy liquid.
Search for potassium argon dating is only done with:
49], the amounts of excess 40Ar and 36Ar found in the flows with anomalous 40Ar/36Ar ratios were too small to cause serious errors in potassium-argon dating of rocks a few million years old or older.'Phenocrysts of orthopyroxene, hornblende and plagioclase are interpreted to have occluded argon within their mineral structures deep in the magma chamber and to have retained this argon after emplacement and solidification of the dacite.