Jökull - 01.12.1989, Side 72

f
. 000
1—
Similarity coefficient
------------------1--------
Elongation
Sphericity
OP index vai
Elongation v.
Fig. 9. Cluster diagram for parameters based on all
samples.
Mynd 9. Línurit yfir fylgni milli þátta. Mœldir eða
útreiknaðir þœttir, sem reynast svipaðir í öllum sýn-
um raðast saman í kippur vinstra megin á grafinu.
Kvarðinn efst á línuritinu er fylgnistuðull Pearsons.
bladed grains. The second sub-cluster contains the
OP-index and its variance, the number of very
elongate and elongate grains, and the Si02 percen-
tage.
The clustering in Fig. 9 indicates that it would be
possible to select one variable from each of the two
major clusters without using any that are based on a
three dimensional analysis, for example elongation
and elongation variance or percentage Si02. How-
ever, the possibility of differentiating between sam-
ples on the basis of sphericity variance (which is
related to the frequency of platy and very platy
tephra grains) would be lost.
REGRESSION ANALYSIS OF
VARIOUS PARAMETERS
Acid magma te'nds'to be highly viscous and is
therefore likely to be drawn into elongate shards as
gas escapes from the rapidly chilling melt.
Although other factors are almost certainly
involved, it is considered a priori likely that a causal
relationship exists between form and magma silicity.
10 50 60 70 80
10 50 60 70 80
Fig. 10. Regression plots for elongation, sphericity,
and OP-index versus Si02. The parameter formulas
are given in the text. Two of the three H, samples
and the duplicate Snæfellsnes sample have been
omitted from the data base to avoid biased weight-
ing.
Mynd 10. Línurit yfir tengsl formþátta við kísilsýru-
innihald gjóskunnar. Endurteknum mœlingum á
sömu sýnum eða sýnum úr sama hluta öskulags er
sleppt. Formþœttirnir eru skýrðir í textanum.
Separate regression plots were drawn for elongation,
sphericity, and OP-index (Fig. 10) and Si02.
Finally, the relationship between two dimensional
and three dimensional parameters was investigated
70 JÖKULL, No. 39, 1989
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