The Yokokawagawa metamorphic rocks (YMR), located east of the Itoigawa–Shizuoka Tectonic Line (ISTL) are considered part of the Sanbagawa metamorphic rocks (SMR) based on zircon U–Pb dating and Raman carbonaceous material (CM) geothermometry. Although previous thermal analyses suggested that the eastern YMR was affected by contact metamorphism related to an andesitic intrusion along the eastern margin, clear mineralogical evidence had not been reported. In this study, we discovered a biotite-bearing sample—characterized by randomly oriented biotite grains cross-cutting schistosity—at the eastern margin and conducted continuous thermal profiling using Raman CM geothermometry. Estimated peak temperatures range from ∼350 to 420 °C and show a V-shaped trend, decreasing from west to east and then increasing. The biotite-bearing sample records ∼400 °C but lacks garnet and plagioclase porphyroblasts, in contrast to the SMR, where these minerals are typically observed at similar temperatures. These findings support the interpretation that the eastern part of the YMR was affected by contact metamorphism caused by an andesitic intrusive body.

Xenoliths of gneissose granitoids within Quaternary dacite from the Daisen volcano in southwest Japan were previously correlated with the Hida granitoids. However, zircon U–Pb dating of two gneissose granitoid xenoliths yields a Late Cretaceous igneous age of ∼ 78 Ma, suggesting a closer affinity with the Late Cretaceous–Paleogene San’in granitoids. Chemical Th–U–total Pb analysis of thorite in one of the xenolith samples yielded scattered apparent ages, with the oldest values approaching the zircon U–Pb age. These gneissose granitoid xenoliths exhibit a granoblastic texture with quartz dioritic modal compositions. Corroded quartz grains are surrounded by a microcrystalline domain consisting of tridymite + oligoclase / anorthoclase + sanidine, interpreted as the result of partial melting during pyrometamorphism within the Daisen dacitic magma. The absence of hornblende and the presence of pyroxene-rich aggregates (orthopyroxene + augite + plagioclase + magnetite) suggest hornblende dehydration melting at ∼ 1000 °C. Biotite was not completely decomposed during high-temperature pyrometamorphism, likely due to its elevated fluorine content (∼ 5 wt% F at grain rims). These mineralogical features are consistent with low-pressure dehydration melting products observed in experimental studies on calc-alkaline granitoids. The gneissose and granoblastic textures are interpreted as original features of the granitoids predating the pyrometamorphic overprint. The exclusive occurrence of Late Cretaceous gneissose granitoids as xenoliths implies the existence of an unexposed plutono-metamorphic complex beneath the San’in region, representing a deeper counterpart of the exposed San’in Batholith.

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.