Ni-bearing minerals such as pentlandite, heazlewoodite, unknown sulfide minerals X, Y and Z are found in the Horoman peridotite, Hokkaido, Japan. Cu-rich mineral of talnakhite, bornite and native copper also occurs associating with Ni-bearing minerals. Pentlandite has the compositional range from 4.276 to 5.238 in atomic ratio of Fe (total atoms=17) changing coexisting minerals. Unknown sulfide mineral X has composition with Cu: 0.010∼0.144, Fe: 5.573∼6.044: Ni: 2.800∼3.392, Co: 0.047∼0.109, S: 7.884∼8.109 in atomic ratio (total atoms=17) and its ideal formula is (Fe, Cu)₆Ni₃S₈. The compositional range of unknown sulfide mineral Y is Cu: 0.573∼1.003, Fe: 5.783∼6.154: Ni: 1.875∼2.392, Co: 0.012∼0.036, S: 7.953∼8.099 in atomic ratio (total atoms=17), and most copper rich end corresponds to CuFe₆Ni₂S₈. Unknown sulfide mineral Z has ideal formula of Cu₂Fe₅Ni₂S₈. Pentlandite and unknown sulfide mineral X occur as primary minerals in the peridotite. Talnakhite and bornite are also found and has their ideal compositions.

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Petrography and petrochemistry of Mn-pyroxenoids in the Mn silicate-oxide and Mn silicate-carbonate-oxide rock assemblages of Precambrian Gangpur Group, Orissa, India are described. The two pyroxenoids, rhodonite and pyroxmangite, appear mutually exclussive of each other. Rhodonite occurs associated with spessartine, Mn-aegirine and tirodite while pyroxmangite coexists with spessartine and tephroite. In the coexisting carbonate members, kutnahorite is associated with rhodonite while rhodochrosite is found with pyroxmangite. Jacobsite is the common oxide present in both the pyroxenoids. Braunite and hematite are the other oxides recorded in rhodonite association in contrast to magnetite with pyroxmangite. The pyroxmangites are richer in FeO and poor in CaO as compared to rhodonites. These two pyroxenoids are considered to have been formed due to decarbonation-oxidation reactions from different progenitors under X_CO2 variation in closed spaced area and strong internal buffering of f_O2 during metamorphism.

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It was a time of unrest for the Japan arc about 15 Myr ago. Magmatism, large-scale topography, and stress regime changed with the rapid paleomagnetic rotation of SW Japan. Magmatic zone expanded oceanward, while the event in NE Japan was older by one million years than in SW Japan. Stress regime in SW Japan changed from tensional to compressional just after the magmatism began.
     Here, a plate kinematic model is presented to account for the events with special reference to the magmatism in SW Japan as a key phenomenon. The magmatism has been ascribed to the subduction of the young Philippine Sea plate. Instead, it is suggested here that the hot mantle plumes that rose under the drifting Japan arc were the cause of the magmatism. A hypothetical microplate, named the Heike, is introduced in the paper. It is assumed that the plate was detached from the Pacific plate at ∼19 Ma and began anticlockwise rotation. The rotation resulted in a leaky transform boundary between the Heike and Pacific plates, creating a slab window that activated fore-arc magmatism NE Japan. Namely, hot mantle materials were raised to compensate the retreat of the Heike slab, and supplied heat to the magmas. Hot and volatile-rich plume was raised from the Pacific slab via the other slab window under western SW Japan by the roll back of the slab, activating the widespread magmatism in SW Japan. The microplate was demised at 15 Ma and the young and buoyant Shikoku Basin begun subduction. The buoyant subduction uplifted SW Japan and switched stress state in the arc. Our plate model is consistent with the superfast Japan Sea opening inferred from paleomagnetic data.

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