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of Kazakhstan, Central Asia, Caucasus, Baikal, Primorye, Omolon and Kamchatka.
They are basically leucite-bearing but silica-rich poptassic variants associated with
them are also found in these localities.
Leucite bearing rocks also have been reported from Alto Paranaiba Igneous
Province of Brazil, Colima volcano of Mexico and Serra Geral Formation of eastern
Paraguay. K-rich feldspathaoidal rocks have been reported also from the Aolean
Arc, south of Italy, Tristan Cunha Islands in the Atlantic Ocean and Utsuryo Island,
Korea. These localities are described below.
4.1 Ultrapotassic Silica-De
cient Rocks from Asia
4.1.1 Leucite-Bearing Rocks of Manchuria, China
The potassium-rich volcanic
fields of Wudalianchi, Erkeshan and Keluo (WEK, NE
China) are located between the Mesozoic Songliao basin and the Palaeozoic Xing
an
Mountains fold belt (Zhang et al. 1995; Fig.
4.1
). The Songliao basin was formed
during Late Jurassic rifting behind the active Paci
'
c margin, and the Palaeozoic fold
'
belts of Xing
an Mountains. The potassic lavas are extended over an area of more
than 1,400 km
2
. Both the Keluo and Wudalianchi
fields are characterized by the
presence of 14 pyroclastic cones, whereas the Erkeshan
field is characterized by the
presence of two volcanoes. Historical records and K
Ar dating show that these
-
potassic rocks erupted during three main episodes:
1. Miocene (9.6
7.0 Ma),
2. Middle Pleistocene (0.56
-
0.13 Ma) and
-
3. Recent (1719
1721 A.D.).
-
110
0
120
0
130
0
50
0
Mesozoic
Volcanic rocks
1
2
3
50
0
Cenozoic
basalt
XM
Fault
40
0
40
0
BEIJING
Fig. 4.1 Map of East China showing the main tectonic domains, distribution of Mesozoic and
Cenozoic volcanic rocks (modified from Fan and Hooper 1991), XM Xing
'
an-Mongolian fold belt.
1 Keluo, 2 Wudalianchi and 3 Erkeshan (after Zhang et al. 1995)
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