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).