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(3) 'flow—layering' exhi)bited by anatexite
are parallel to the contact and contact
irregularities.
C) presence of areas of breccia development.
These field relations, schematically illustrated in
Fig. 3, can best be explained by assuming the peripheral
development of migma ,in the country rocks surrounding
the cupola of gabbro.
Breccia development appears to be, in part, the
product of an irregular cooling history involving magma
pulsatidn followed by fissuring and intrusion of more—
peripheral areas.
Note the abundant xenoliths in the gabbro (apparently
reflecting the 'high' level of cupola exposure); the
rheomorphic dikes of granophyre with tourmaline±prehnite
in the anatexites; and dikes of laurvikite in the gabbros.
The laurvikite dikes commonly show;
(1) angular inclusions of gabbro,
obviously locally derived;
(2) contact relations indicative of
emplacement during periods of
extension;
(3) composite appearance.
Thin âections of the anatexites show porphyroblasts of
•(in decreasing order of relative abundance); clinopyroxene,
IC—spar, quartz, orthopyroxene (Fs 25—35), biotite, oxides,
and sulfides. l4ineralogically the anatexites lie within
the orthopyroxene clinopyroxene — plagioclase triangular
field of an ACF plot for the pyroxene—honfels fades.
Physical and/or optical alignment of some of the minerals
especially plagioclase (An20 to An40), is not uncommon.
The gabbros vary from fine to coarse grained but all
varieties are essentially anhydrous two pyroxene gabbros
with or without phenocrysts of plagioclase of (An65_70).
The medium to coarse gabbros of 'Inner Border Zone A' show.
anomalous amounts of quartz and K—spar, probably due to
assimilation.
OO
Thin sections of the syenite dikes, generally composite,
show perthites (generally extensively exsolved, patch
perthite) with varying proportions of aegirine—augite,
riebeckite, calcite, zircon, fluorite, quartz, and oxide
(ilmenite ± magnetite). These dikes are considered to be
apophyses from the main body of laurvikite.
Turn round and proceed north towards Marathon.