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Fig. 4.34 continued
ned trends with
increasing differentiation, which are consistent with fractional crystallization. The
mg-numbers range from 40 to 62. There is also co-variation with certain minor and
trace elements (e.g. Sr, Ba and P). This suggests the presence of at least two distinct
fractionation trends. The Sr, Nd and Pb isotopic analyses of a subset of the lavas
show the
Major and trace element variations in the lavas present well-de
87
Sr/
86
Sr
143
Nd/
144
Nd
following
ratios,
(0.70495
0.70517),
-
206
Pb/
204
Pb (18.47
(0.51259
18.74). Phonotephrites range from
moderately plagioclase-phyric to aphyric in texture and comprise plagioclase
(An
88
-
17
), clinopyroxene (Wo
49
-
47
En
41
-
37
Fs
11
-
15
), titano-magnetite and kaersu-
tite. Apatite is an abundant accessory mineral. Alkali feldspar (Or
12
-
19
Ab
72
-
64
An
16
-
17)
and leucite occurs as late crystallizing product as a groundmass phase.
Tephri-phonolites are characterized by the presence of kaersutite, titano-magnetite
(Usp
38
-
51
), plagioclase (An
62
-
46
), clinopyroxene, sphene and apatite. Phonolites
comprise alkali feldspar, plagioclase, kaersutite, clinopyroxene, apatite, ilmenite,
ha
0.51247), and
-
-
yne and sodalite. Melting relations of Tristan da Cunha rocks were studied by
Tilley et al. (1965).
ΓΌ
4.13.3 Trachyte-Phonolite-Bearing Lavas of Ulleung Island,
South Korea
Brenna et al. (2014) studied the lavas of Ulleung Island, South Korea. Ulleung
Island refers to the top of a 3,000 m (from sea
floor) intraplate alkali volcanic
edi
ce in the East Sea/Sea of Japan. The 950 m high lava pile consists of a alkali
basaltic lavas and agglomeratic succession (Stage1, 1.37
0.97 Ma), intruded and
overlain by a sequence of trachytic lavas and domes, which erupted in two episodes
(Stage 2, 0.83
-
0.24 Ma). Geological setting and digital
elevation model for the Ulleung Island (900 m above the sea level is shown in
0.77 Ma; Stage 3, 0.73
-
-
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