3.1. Pyroxenites
The pyroxenite lenticular bodies can be recognized in the field by their
fresh appearance, green to orange color, and medium-to-coarse grained
cumulate texture. In map view (Fig. 2), these lenses are 0.5 to 2.5 km
long and 0.1 to 0.3 km wide. Their composition varies from pure
clinopyroxenite to websterite with an approximate
orthopyroxene/clinopyroxene ratio of 1:3. The olivine varieties (up to
25 vol.%) are made of olivine clinopyroxenite and olivine websterite
(Fig. 3a). In some samples, plagioclase (<3 vol.%) is
interstitial. Pyroxenite bodies are internally composed of alternating
meter scale to millimeter scale layers of clinopyroxenite with
clinopyroxene-dominant websterite and olivine clinopyroxenite with
subordinate olivine websterite (Fig. 3b). Contacts between pyroxenites
and nearby gabbroic rocks are not exposed. The pyroxenites commonly do
not show a deformational fabric, but recrystallization is indicated in
some samples by porphyroblasts in thin section.
Clinopyroxenite and olivine clinopyroxenite are medium- to
coarse-grained and display a hypidiomorphic to idiomorphic granular to
granoblastic texture. They contain unaltered green clinopyroxene (92-99
vol.%) with olivine (0-8 vol.%), minor orthopyroxene (0-8 vol.%) and
green spinel (<2 vol.%) (Fig. 4). Clinopyroxene textures
range from euhedral adcumulate to mesocumulate (Fig. 5h) and
granoblastic, where smaller recrystallized polygonal grains surround
large magmatic clinopyroxene grains. Exsolution of orthopyroxene in
clinopyroxene is ubiquitous. Orthopyroxene is subhedral. Olivine forms
large subhedral grains or occurs as an equigranular polygonal mosaic
(Fig. 5g). Spinel occurs as discrete grains and as exsolution lamellae
in clinopyroxene.
Websterite and olivine websterite are medium- to coarse-grained and
range from adcumulate to orthocumulate and recrystallized granoblastic
in texture. They are composed of 65-75 vol.% clinopyroxene that has
exsolution lamellae of orthopyroxene, and 25-35 vol.% orthopyroxene
with a pink-green pleochroism and exsolution lamellae of clinopyroxene
(Fig. 4). Olivine forms large subhedral grains (0-22 vol.%). Relic
igneous textures indicate adcumulus growth. In recrystallized rocks,
orthopyroxene and clinopyroxene form intergrowths with curved cuspate
contacts. Euhedral Mg-Al spinel is rare (<1 vol.%) and has a
slight greenish tint. Plagioclase occurs as an intercumulus phase
forming a subequigranular mosaic (<5 vol.%).
Plagioclase-bearing websterite also appears as centimeter scale pockets
in the massive websterite.