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orthopyroxene is not present in the Jarangdih lamproite, it is observed as a phase in
the high pressure runs. Ryabchikov and Green (1978) studied a mafurite in presence
of variable CO 2 and H 2 O. They noted that in presence of high CO 2 content orth-
opyroxene appeared as a phase even through the mafurite did not contain ortho-
pyroxene. In their study of an armalcolite-bearing lamproite, Edgar et al. (1992)
also observed the presence of orthopyroxene at pressure above 1.0 GPa although it
is not present in the natural rock. The presence of orthopyroxene at high pressure
may be related to the following reaction:
Mg
SiO 4 +CO 2 ,
MgSiO
+ MgCO
2
3
3
The carbonate-bearing phase appearing as the last phase may be enriched in this
component. Electron microprobe studies showed that La 2 O 3 (0.35
0.42) and Ce 2 O 3
-
(O.78
C and 1.0 GPa are high. It
suggests that this accessory apatite in the mantle harzburgite may be a possible
source of LREE in these rocks.
O.89) contents of the apatites appearing at 800
°
-
13.2.6.2 P
T Study on a Phase Relations in a Mohanpur Lamproite
(Raniganj Basin)
-
Experimental studies on Mohanpur Lamproite are summarized in Fig. 13.10 , which
shows the appearance of following assemblages with progressive lowering of
temperature:
Fig. 13.10 Phase relations of a lamproite from Mohanpur (Raniganj Basin) (after Gupta et al.
2002). For abbreviations, see Fig. 13.7 . prid: priderite, chr: chromite. Other abbreviations are the
 
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