Quartz occurs ubiquitously in felsic plutons. The development of a methodology to reveal the quartz growth process in a granitic body provides essential insights into magma chamber processes. Cathodoluminescence (CL) characterization combined with Ti concentration of quartz crystals in granite is a prevalent tool for identifying the crystal growth and crystallization temperature of quartz in granitic magmas. This study focused on quartz crystal growth in the Kuki granite (KKG), northeast Japan, and Kurobegawa granite (KBG), central Japan. In the KKG quartz crystals, the difference in luminescence corresponds to Ti concentration: high luminescence corresponds to high Ti concentrations, which is consistent with our previous studies on the Toki and Okueyama granites. In the KBG quartz crystals, the Ti concentrations do not correspond to the luminescence level, whereas the Al concentrations are negatively correlated with the luminescence level. Therefore, quartz crystallizations in KKG and KBG are characterized by Ti- and Al-diffusion-controlled growth, respectively. Using the difference in the time–temperature history among the target rock bodies, this study provides insight into the nature of the relationship between quartz crystallization and magma chamber processes. Quartz crystallizations in the KKG were accompanied by gradual variations from oscillatory zonation through gradual zonation to homogeneous CL patterns with decreasing temperature in the cooling magma chambers. The quartz internal structure of the KBG was resulted from the rapid cooling of the KBG magma and the scarcity of Ti and enrichment of Al in the magma during quartz crystallization.

We investigated the synthesis conditions of metastable α-cristobalite using amorphous silica (silica-gel) with and without V₂O₅ as a flux. Secondary electron microprobe observations for synthesized samples with flux revealed the formation of faceted α-cristobalite crystals (2–19 μm), whereas those synthesized without flux did not exhibit a clear facet. Powder X-ray diffraction analysis showed that the addition of flux lowered the formation temperature of metastable α-cristobalite to 1000°C, which contrasts with the fact that the crystallization occurred at 1200°C in the case without flux. These observations demonstrate that the V₂O₅ flux alone promotes crystallization by lowering the activation energy of the crystallization process of metastable cristobalite as well as other kinds of flux materials.

This study presents petrological and whole-rock geochemical data on basaltic lavas from the Tewa Zobar region of the northwestern Ethiopian plateau to investigate their petrogenesis, with petrographic analysis indicating the lavas consist of plagioclase, pyroxene, olivine, and Fe-Ti oxide minerals, exhibiting aphanitic, porphyritic, and glomeroporphyritic textures. Most of the basaltic samples (MgO = 7.4 wt. % - 7.9 wt. %) show alkaline composition, with the exception of one sample with lower MgO content of 6.4 wt.% showing a sub-alkaline nature. The alkaline basalts show steep primitive mantle-normalized trace element patterns with elevated high-field strength elements (HFSE) and heavy rare earth element (REE) profiles, including higher (Sm/Yb)_N, (La/Yb)_N, and (La/Sm)_N values, whereas the sub-alkaline rock sample #Z56 has flatter heavy-REE profiles with lower (Sm/Yb)_N, (La/Yb)_N, and (La/Sm)_N values. Based on the REE model, the sub-alkaline basalt suggests a melt fraction of 3-4%, while the alkaline basalt indicates a lower melt fraction of 1-2%, accompanied by approximately 1-2% residual garnet of enriched mantle source. These basalts also exhibit enriched trace element patterns, with the (Nb/Th)_PM ratios typically showing a higher range, while the sub-alkaline basalt displays a notably lower Nb/Th ratio. Additionally, the alkali basalts generally have a higher Nb content relative to La, with (Nb/La)_PM ratios showing a narrow range, while the sub-alkaline basalt presents a lower Nb/La ratio. The alkaline basalts analyzed, with element ratios such as La/Nb, Ba/Nb, and Ba/La —excluding Sample Z56, which shows distinct values—fall within the range of mantle-derived basalts, indicating the absence of crustal contamination. The middle rare earth element (MREE)/heavy rare earth element (HREE) and light rare earth element (LREE)/HREE ratios indicate that the basaltic magma was derived from a mantle source in the garnet-spinel transition zone at ∼80 km depth, with small degree of melting and significant contributions from both subcontinental lithospheric mantle (SCLM) and asthenospheric sources. Elevated Zr/Hf values and high incompatible trace element enrichment suggest that small-volume metasomatic fluids may have enhanced the source region. The elevated Nb/Ta ratio in the mafic lavas suggests the magma likely originated from a SCLM, potentially modified by metasomatic processes involving carbonatite-like component, while the geochemical similarities between the alkaline basalts and high-Ti 1 (HT1) magmatism point to a connection with mantle plume activity, which may have influenced the recent eruptions on the northwestern Ethiopian plateau.