Experimental Studies on K-Rich Rocks - Origin of Potassium-rich Silica-deficient Igneous Rocks - page 374

Chapter 13
Experimental Studies on K-Rich Rocks

13.1 Investigations of Leucite-Bearing Rocks Under
Atmospheric Pressure

Experimental studies on potassic rocks from Leucite Hills Wyoming, U.S.A. by
different investigators are summarized in Table 13.1 . Wyomingites and orientates
reported in this table are from the same locality, but the samples are different with
slightly different chemistry, hence variation in liquidus temperatures of different
primary phases are expected. It may be observed that the liquidus temperatures in
case of the runs conducted by Yagi and Matsumoto are higher than average tho-
leiitic or alkali basaltic rocks (Yoder and Tilley 1962). Although textural studies
indicated that leucite is the liquidus phase in the cases of wyomingite and orendite,
clinopyroxene always appeared as the first phase in their atmospheric runs. This

was interpreted by them to be due to loss of water in their one atmospheric runs.
Table 13.1 shows that there are large differences between the liquidus and solidus
temperatures in case of the experimental runs performed by Fyfe (quoted in Car-
michael 1967). On the basis of this observation, Carmichael concluded that rocks of
Leucite Hills are product of a magmatic liquid formed at great depth in the mantle.
Gupta et al. (1983) made quenching experiments on four lamproitic rock sam-
ples collected from dykes intruding Gondwana rock formations in the Damodar
Valley regions (see Chap. 4 ). The two localities (Raniganj and Jharia Coal Fields)
from where the samples were collected are respectively 200 and 250 km west of
Kolkata. The powdered rock samples were heated in sealed capsules under atmo-
spheric pressure and NNO buffer conditions. Analyses of the four rock samples
from Sudamdih (S), Mohanpur (M-2 and M-3) and Poidih (P) are shown in Table 4.2 .
Results showed that the primary phases, liquidi and solidi are as follows: S: Leucite,
1,305 and 1,185 ° C; Leucite, 1,245 and 1,150 ° C; M-2: Olivine, 1,250 and

1,150 ° C; M-3: Leucite, 1,242 and 1,150 ° C and P: Olivine, 1,235 and 1,100 ° C.