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potassic-richterites; also, different partitioning patterns are apparent for REE and
LIL elements, where S, L and D refers to solid, liquid and distribution coef
cient.
These differences discussed by Tipolo et al. (2003) are described in terms of the
distinct crystal-chemical behaviour of the involved amphibole-end-members, with
particular emphasis to the available charge balance mechanisms and to the site
dimensional constraints resulting in incorporation of trace elements in various sites.
The distinct partitioning behaviours of trace elements in potassic-richterites and
pargasites and kaersutites imply that melts produced from amphiboles-bearing
sources may differ markedly depending on the type of amphiboles crystallised. The
new partitioning data may be used to determine the role of potassic-richterite in its
principal modes of occurrence, namely in lamproites, in peralkaline ultrama
c veins
in the lithospheric mantle, and in the deeper parts of subduction zones.
2.7 Olivine
Olivine is an important mineral in leucite-bearing basanites, lamproites, minettes
(with high mg-numbers), katungite and mafurites, where it occurs as phenocrysts
(Fo
84
-
92
) and megacrysts (Fo
88
-
92
, Table
2.7
). In the potassic rocks of Alto Par-
anaiba Igneous Province (Gibson et al. 1995), olivine exhibits slight compositional
variation, whereas olivine inclusions show compositional zonation (Fo
84
-
87
).
Both phenocrystal and groundmass olivines are present in olivine orendites
(Kuehner et al. 1981) from Spring Boat, North Table Mountain and South Table
Mountain (Leucite Hills, Wyoming, U.S.A., Table
2.7
). Leucitites occurring in
New South Wales, Australia (Cundari 1973), are characterised by olivine (Fo
93
-
79
)
phenocrysts (0.3
3.0 mm along c-axis, Table
2.7
). Iddingsites (pseudomorph after
olivine) are common.
Orciatico lamproites (Italy) have olivines having wide range of compositions
(Fo
74
-
-
Fo
92
) with no chemical zonation. The CaO and MnO content of the olivines
increase systematically with decrease in the forsterite content. Large rounded
crystals with kink banding are very much common in the Orciatico lamproite.
Brown Leucitic Tuffs from Latera Caldera (Luhr and Giannetti 1987; Table
2.7
)
are characterised by the presence of forsteritic olivines (Fo
82
-
91
). The rims and
fractures within olivines are
filled by iddingsites. Diopside crystals often form
clusters with olivines, which are probably xenocrysts. Olivine occurs in the basa-
nites of Mt. Vulture complexes. It is usually found as a phenocryst, intergrown with
diopside. This phase however, does not show any reaction rim. The olivine grains
have narrow compositional range (Fo
89
-
88
, Table
2.7
).
The leucite-bearing lavas of EK series from Ringgit
Beser complex, East Java
(Edwards et al. 1994) contain phenocrystal forsteritic olivine (Fo
91
-
92
). They have
quenched skeletal textures and show alteration to iddingsite. Olivine phenocrysts
(Table
2.7
) in the minettes from Bearpaw Mountains, Montana (Macdonald et al.
1992) are usually idiomorphic and 3 mm long. Some crystals show resorption.
Normal zoning towards Fe, Mn and depletion in Ni is quite common. Olivine
-
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