Geology Reference
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Ar technique yielded an age of
20 million years for the whole-rock from Gaussberg. According to Sheraton and
Cundari, Gaussberg has a tectonic setting on a passive continental margin.
Gaussberg lies at one end of the so-called Kerguelen Gaussberg Ridge. The rocks
are characterized by the presence of subhedral crystals of olivine, clinopyroxene
and leucite (up to 1 mm across) in a yellow-brown glassy matrix. Phlogopite and
amphibole also occur as late crystallizing phases. The Mg/(Mg + Fe) ratio of the
rocks is around 0.70.
The phlogopites are titaniferous with high BaO (1.0 wt%) and are similar to the
micas of West Kimberley (in composition). The rocks are essentially leucitite with
chemistry similar to those of Leucite Hills, Wyoming (U.S.A.) and West Kimberley,
Australia.
According to Sheraton and Cundari (1980) the glass is characterized by the
presence of quench crystals of leucite, diopside, phlogopite, amphibole and
ilmenite. Chromite constitutes about 50
According to Sheraton and Cundari, the K
-
60 vol% of the whole rock. The Gaussberg
rocks are highly potassic (K 2 O content around 12 wt%) with K 2 O/Na 2 O ratio being
close to
-
five. The alumina content is lower than the total alkali content. The olivine
leucitites from Gaussberg also contain cognate xenoliths of phlogopite and olivine-
bearing leucitite. It may also include accidental xenoliths of spinel lherzolite.
There are also two isolated K-rich dykes in the Australian Antarctic territory.
One of the dykes is five metre thick and located at Mt. Bayliss (73 ° 26 S, 62 ° 50 E)
in the southern Prince Charles Mountains, MacRobertson land. According to them
the K
10 million years for these
dykes. Age determination of a K-arfvedsonite, occurring within the rock yielded an
age of 430
Ar dating of K-richterites suggests an age of 413
±
-
E) in
Enderbyland is essentially a phlogopite-bearing syenite, termed melasyenite by
Sheraton and England (1980).
According to them Mount Bayliss rocks show textural evidence indicating
reaction of leucite with liquid to form K-feldspar.
The three Antarctica lamproites are enriched in TiO 2
±
12 million years. The other dyke at Priestly Peak (67
°
11
S, 50
°
12
(3
5 wt%), P 2 O 5
-
(1.5
3.3 wt%) and lithophile elements (Ba: 400
1,500 ppm, Zr: 900
1,800 ppm;
-
-
-
Sr: 1,300
3,000 ppm; Nb: 40
150 ppm and Ce: 270
335 ppm).
-
-
-
4.5 Potassium-Rich Silica-Undersaturated Igneous Rocks
of the United States of America
4.5.1 Volcanic Fields of Highwood Mountains, Montana
The petrographic province of the Highwood Mountains (Fig. 4.12 ) was studied by
Larsen and Buie (1938), Larsen et al. (1941), Marvin et al. (1980) and more
recently by O
'
Brien et al. (1988, 1991). It is a deeply eroded volcanic and intrusive
complex (52
±
1 Ma). The volcanic
field is characterized by an older series of
 
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