Jökull - 01.01.2001, Síða 60

Ármann Höskuldsson
Table 2. Major element analysis of the pumice from the pyroclastic–fall deposit, dome rocks and whole rock
sample from the pyroclastic flow deposit. All analyses were carried out on an ICP–argon plasma spectrometer
in Clermont Ferrand. The 2 s error is about 2% for SiO and 5% for other elements. – Aðalefnagreiningar af
vikrinum, hraungúlnum og gjóskuflóðasetinu. Allar efnagreiningar eru gerðar með ICP–argon plasma spektró-
meter í Clermont Ferrand.
Sample/sýni BC1 PA98 PA96(I) PA96 (II) PA91
ash–flow/aska dome/hraungúll pumice/vikur pumice/vikur pumice/vikur
SiO 61.8 63.5 70.4 69.8 69.84
TiO 0.2 0.58 0.21 0.2 0.16
Al O
15.88 15.82 13.8 13.68 13.87
Fe O
04.9 4.72 1.27 1.28 1.17
MnO 0.07 0.09 0.07 0.07 0.07
MgO 2.41 3.18 0.34 0.38 0.29
CaO 4.5 4.39 1.22 1.35 1.42
Na O 3.5 4.03 4.3 4.17 3.94
K O 1.82 2.48 3.72 3.65 3.99
P O 0.19 0.18 0.08 0.08 0.06
H OPF 4.2 0.22 4.2 4.33 3.61
Total/samtals 99.94 99.17 99.53 98.99 99.15
Figure 10. Total alkali–silica classification of the
magma extruded during the las Cumbres eruption (open
squares). The dots are rock analysis from the neigh-
bouring volcano Pico de Orizaba and marginal cinder-
cones (Höskuldsson, 1992). All analyses normalized
to 100% anhydrous before plotting. The dotted area in
the basaltic field of the diagram indicates those rocks
containing (ol) and (cpx) phenocrysts (Robin, 1981;
Gourgaud, 1985). – Alkalí–kísil flokkun bergtegunda
sem upp komu í gosinu (opnir ferningar). Punktar sýna
efnasamsetningu nágrannaeldfjallsins, Pico de Orizba,
og smágíga á sléttunni umhverfis eldfjöllin. Allar efna-
greiningar eru leiðréttar með tilliti til vatns.
and Huddlestun, 1972). Glacially derived sediments
on and around Mexican volcanoes suggest increased
glacial activity during the Wisconsin (White, 1987;
White and Valastro, 1984; Heine, 1988). This evi-
dence suggest that at about 16 ka, the Cerro las Cum-
bres cone was covered by an ice cap. This high–
altitude water/ice reservoir had a strong influence on
the progress of the 16 ka eruption as indicated by the
occurrence of phreatomagmatic deposits in the Cerro
Las Cumbres eruption succession.
60 JÖKULL No. 50