Figure 2. Representative thin section microphotographs and scanning electron microscopic images of samples from the Isua supracrustal belt. a: Sample AW17724-2C preserves primary olivine grains (i and ii). There may be two generations of serpentine minerals (ii): serpentine minerals that might be inclusions in the olivine grains, and serpentine minerals occur as lepidoblastic assemblages in the matrix cutting olivine, magnesite, and Ti-humite. Alternatively, there may be only one generation of serpentine minerals with those in the olivine being associated with cracks or veins not visible on this thin section plane. Due to the observed alteration, primary igneous textures of this sample cannot be identified. b: Local preservation of polygonal textures (i) by olivine grains in sample AW17725-4. Olivine in this sample contains abundant magnesite and rare serpentine (ii), which may represent inclusions or alteration products.c–d: Loss of most primary ultramafic silicates and rock textures of some Isua samples due to strong alteration (e.g., serpentinization, talc alteration, and/or amphibolite facies metamorphism). Mineral abbreviations: mag: magnesite; mgt: magnetite; ol: olivine; serp: serpentine; Ti-cl: Titano-clinohumite; Ti-ch: Titano-chondrodite; tr: tremolite.