Geology Reference
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phonolites and (3) a subvolcanic layer comprising olivine, clinopyroxenite, leucite
and orthoclase-bearing pyroxenite (
(first phase), alkali monzonite, shonkinite and
syenite (second phase), pyroxene-bearing syenite and nepheline syenite (third phase)
and
finally syenite porphyry (fourth phase of volcanic activity).
4.12.9 Kolbashinskii (42 ° 20 N, 73 ° 44 E)
Leucite-bearing ma
c rocks including leucite tephrite, alkali trachytes, tuffs, breccia
and peralkaline trachyte (270
309 Ma) occur in a volcanic
field in an east
west-
-
-
trending zone (40
50 km long, 5 km wide) located in the Kirgiz shield of the
northern Tyan-Shan region, west of lake Issyk-Kul (Bagdasarov et al. 1974).
-
4.12.10 Synnyr (56
55
N, 111
20
E)
°
°
The Synnyr pluton (Baikal province) is an oval-shaped body intruding into a
sedimentary sequence of Cambrian limestone, conglomerate and sandstone and
Palaeozoic granitoids. From core to the rim following succession of rocks occur in
following order: alkaline syenite, pseudoleucite syenite, microcline pseudoleucite
syenite and nepheline syenite. At the central part the oval-shaped stock (100 km 2 ),
is an igneous complex comprising trachyte and pyroxene-syenite (pulaskite). One
of the varieties of pseudoleucite-bearing rocks is synnyrite, consisting of microcline
and intergrowth of orthoclase, nepheline and kalsilite. In the intergrowth, the ratio
of K-feldspar to kalsilite (
nepheline) varies between 67 and 33 vol%. The K 2 O
content of these rocks may be as high as 18
±
20 wt%. The vol% of pseudoleucite
-
may be as high as 50
60 %. The nepheline syenites are miaskitic and 311 Ma year
old (Zhidkov 1990). During the
-
final stage, dykes of tinguaite, shonkinite, camp-
tonite and monchiquite were emplaced.
4.12.11 Yaksha (56
55
N, 111
48
E)
°
°
A plutonic dome comprising silica-undersaturated alkalic rocks occur at Yaksha.
The larger part of the complex is made up of syenite, comprising K-feldspar and
micro-perthite (60
12 %), with an
admixture of nepheline and albite. The accessory phases include apatite and sphene.
Nepheline-kalsilite intergrowth and kalsilite-bearing syenites are closely mixed
with each other. Nepheline-kalsilite syenite or kalsilite-syenite (synnyrites) is rare.
According to Kogarko et al. (1995),
80 %), pyroxene (5
15 %) and biotite (3
-
-
-
the pseudoleucitic rocks with preferred
 
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