The oxidation states of Fe within olivine, orthopyroxene, clinopyroxene, and spinel in a spinel lherzolite xenolith from the Tariat Depression, Mongolia were investigated using ⁵⁷Fe Mössbauer spectroscopy to evaluate the redox condition of the upper mantle from which the Tariat spinel lherzolite xenolith was derived. The purity of separated minerals for the Mössbauer spectroscopic analysis was examined using X-ray powder diffraction, Raman spectroscopy, and transmission electron microscopy. Average Fo and Fe contents of olivine at the core part of the xenolith are 89.9(4) mol % and 0.195(3) atoms per formula unit, respectively. The Fe³⁺/ΣFe values of the olivine, orthopyroxene, clinopyroxene, and spinel, determined by Mössbauer spectroscopic analysis, are 0.027(2), 0.15(1), 0.26(3), and 0.34(5), respectively. The Mössbauer spectrum of olivine consists of two doublets assigned to Fe²⁺ at the octahedral sites and one doublet, with I.S. of 0.40(2) mm/s and Q.S. of 0.69(3) mm/s assigned to Fe³⁺ at the octahedral site. Since the Tariat spinel lherzolite xenolith in this study shows no evidence of metasomatism or thermal alteration, the existence of a small amount of Fe³⁺ in olivine and the fairly high Fe³⁺ contents of clinopyroxene, orthopyroxene, and spinel imply that the upper mantle under the Tariat area was in a rather oxidized condition.

The Sør Rondane Mountains, East Antarctica have been thought to be situated in the collision zone between East and West Gondwana during the final stage of amalgamation of the Gondwana supercontinent. They are therefore recognized as a key region for understanding the geological phenomena during the collisions and for testing the proposed tectonic models. We identified metamorphic rocks with different pressure–temperature–time paths that are bounded by a ductile shear zone at Oyayubi ridge, Brattnipene, Sør Rondane Mountains. Based on field and microscopic observations, chemical analyses of minerals, and zircon U–Pb dating, the sillimanite–garnet–biotite gneisses (i.e., pelitic gneisses) from higher structural level show a peak metamorphism at ca. 590 Ma that took place under conditions of ca. 830–840 °C and 0.8–0.9 GPa, and these high-temperature conditions lasted until ca. 550 Ma. These rocks underwent isothermal decompression and then retrograde hydration under lower pressure–temperature conditions than 530 °C and 0.4 GPa at ca. 530 Ma. In contrast, the orthogneisses that consist of hornblende–biotite gneiss and garnet–clinopyroxene gneiss from lower structural levels did not undergo metamorphism at ca. 600 Ma, but underwent metamorphism at ca. 570 Ma and reached peak conditions of 700–760 °C and 0.6–0.9 GPa at ca. 560–550 Ma. These observations suggest thrusting of the pelitic gneiss over the orthogneiss at ca. 570–550 Ma, causing a prograde metamorphism of the orthogneisses and a decompression of the pelitic gneisses as well as uplift and subsequent rapid denudation. The results indicate two stages of collision in the Sør Rondane Mountains, and that the ductile shear zone that bounds the pelitic gneiss and orthogneiss units may have been part of the continental plate collision boundary at ca. 570–550 Ma.

Gem-quality zircon megacrysts occur in placer deposits in the Central Highlands, Vietnam, and have euhedral to anhedral crystal shapes with dimensions of ~3 cm in length. These zircons have primary inclusions of calcite, olivine, and corundum. Secondary quartz, baddeleyite, hematite, and CO₂ fluid inclusions were found in close proximity to cracks and tubular channels. LA-ICP-MS U-Pb ages of analyzed zircon samples yielded two age populations of ca. 1.0 Ma and ca. 6.5 Ma, that were consistent with the ages of alkali basalt eruptions in the Central Highlands at Buon Ma Thuot (5.80–1.67 Ma), Pleiku (4.30–0.80 Ma), and Xuan Loc (0.83–0.44 Ma). The zircon geochemical signatures and primary inclusions suggested a genesis from carbonatite-dominant melts as a result of partial melting of a metasomatized lithospheric mantle source, but not from the host alkali basalt. Chondrite-normalized rare earth element patterns showed a pronounced positive Ce, but negligible Eu anomalies. Detailed hyperspectral Dy³⁺ photoluminescence images of zircon megacrysts revealed resorption and re-growth processes.