petrology of ultramafic and related rocks along iraqi zagros thrust zone

3-1-4 Chromitite
The chromitites are hosted in harzburgite, although they are
typically enveloped by dunite. The chromitites bodies are mainly lensoidal
in form (Fig. 3-4), but some occur as veins, stringers and linear or planer
seggregation (Fig. 3-5). The dimensions are highly variable, generally
ranging from 2 to 3 m long and 0.5-2 m thick. Most chromitite bodies are
concordant with the foliation in the host peridotite. The contacts between
the chromitites and host dunites or harzburgites are usually sharp, but
some chromitite bodies grade into the duite envelope by increasing in
modal olivine. Most of the chromitites have massive (> 80 % chromite) or
disseminated texture. Chromite in the massive chromitites is typically
medium grained (1-4 mm across). Disseminated chromitites occur as
aggregates of 0.5-1mm crystal. Common banded texture is also present.
Olivine and tremolite, the most abundant silicate minerals in the
chromitites, occur as matrix minerals and as inclusions in chromite.
3-1-5 Hornblendite
Hornblendite is hosted in harzburgite. Hornblendite bodies are always
lensoidal in form (Fig. 3-6). The dimensions are highly variable, generally
ranging from 2 to 3 m long and 0.5-2 m thick. Most hornblendite bodies are
concordant with the foliation in the host peridotite. The contacts between
the hornblendite and host harzburgite are typically sharp. All hornblendite
lenses have granular texture, in which hornblende is the major minerals
(90 vol. %), with some plagioclase (7 vol. %), and accessory ilmenite.
Hornblende is typically medium grained (0.5-2 mm across) and plagioclase
mostly occurs as rounded grain with 0.2-1 mm across. Oriented inclusions
of ilmenite are abundant in the core of hornblende crystals. A hornblendite
lens at the main thrust fault contains lensoidal rock of centimetric scale
(Fig.3-7). It has mineral assemblages rutile + Cl-apatite + ilmenite +
chlorite + amphibole ± pyroxene.
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