Fig. 4. (a–b, e–m) Photomicrographs and (c–d) back-scattered
electron (BSE) images of the studied samples. Abbreviations: olivine:
Ol; clinopyroxene: Cpx; orthopyroxene: Opx; garnet: Grt; amphibole: Amp;
spinel: Spl.
There are three types of olivine in the samples. The first type
(Ol1) occurs as fine-grained inclusions in garnet and
clinopyroxene porphyroblasts (Fig. 4a–b). These inclusions are rounded
and crystallized earlier than the coarse-grained garnet and
clinopyroxene porphyroblasts. The olivine inclusions have MgO =
40.55–41.25 wt.%, FeO = 18.52–19.97 wt.%, and Mg#= 79–81. The second type (Ol2) is coarse-grained
olivine porphyroblasts that are ~2 mm in size, which are
in equilibrium with coarse-grained garnet, clinopyroxene, and
orthopyroxene porphyroblasts (Fig. 4e–g). The coarse-grained olivine
contains mesh-like fractures that are mostly infilled with serpentine.
These olivines are elongate and their long axes are oriented E–W,
similar to the foliation in the surrounding gneiss. The axial ratios of
the coarse-grained olivine are mainly 1.2–2.8, with a maximum of 5.6
(Fig. 5a). The olivine porphyroblasts have MgO = 38.99–40.33 wt.% and
FeO = 18.74–21.66 wt.% (Fig. 6a), and Ca = 30.91–311.77 ppm, Ti =
3.33–26.54 ppm
(Fig.
6b), Ni = ~700–900 ppm, and Cr = 0.32–33.78 ppm (Fig.
6c). The third type (Ol3) is fine-grained matrix olivine
with diameters of <0.2 mm. The fine-grained matrix olivine
grains surround the coarse-grained olivine, garnet, clinopyroxene, and
orthopyroxene (Fig. 4b, d, h, and j), and occur in narrow cracks in
coarse-grained garnet porphyroblasts (Fig. 4i). This indicates that the
matrix olivine crystallized at a late stage. The fine-grained olivine
grains also exhibit obvious elongation and a long-axis orientation
similar to that of the coarse-grained olivine. The axial ratios of the
fine-grained olivine grains are mainly 1.2–3.0, with a maximum of 8.4
(Fig. 5b). The matrix olivine grains have MgO = 38.04–39.06 wt.% and
FeO = 20.57–21.85 wt.%. The Ca, Ti, and Cr contents are high and
variable (Fig. 6b–c). From the olivine inclusions to the olivine
porphyroblasts and to the matrix olivine, MgO contents decrease, FeO
contents increase (Fig. 6a), and Ca, Ti, and Cr contents increase (Fig.
6b–c).