This paper reports on the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb dating of zircon and on the field emission electron probe microanalyzer (FE-EPMA) U-Th-Pb dating of monazite from pelitic granulites and the surrounding Itoshima granodiorite from the Mt. Ukidake area, Sefuri Mountains, northern Kyushu. Zircons from the Itoshima granodiorite give an age of Ma. Metamorphic domains within zircons from pelitic granulites yield a slightly older age of Ma, which is consistent with ages of-Ma obtained from analysis of monazite by U-Th-Pb dating using FE-EPMA. Analysis of inherited domains within zircons from the pelitic granulite gives a narrow range of ages from to Ma, with a youngest age of Ma. These ages are comparable with those of the Renge metamorphic rocks in north Kyushu, although the age and conditions of metamorphism at Renge are significantly different from the granulites analyzed here. Metamorphic ages for the granulites are nearly identical to the reheating age of the Higo metamorphic rocks in central Kyushu, as well as the main metamorphic age of the Ryoke metamorphic rocks in southwest Japan. However, the age distributions of detrital zircons from the Mt. Ukidake area are different from those of the Higo and Ryoke metamorphic rocks, implying a different provenance for each metamorphic rock unit.

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The Cretaceous Ushikiri-yama granodiorite is exposed in the northern part of Tagawa city (Fukuoka Prefecture, SW Japan) and is part of the North Kyushu batholith. Three types of dikes with varying compositions are associated with the Ushikiri-yama granodiorite: porphyritic fine-grained diorite (Pr Fine Di), porphyritic finegrained tonalite (Pr Fine To), and porphyritic fine-grained granite (Pr Fine Gr). The granodiorite intrudes the pre-Cretaceous basement rocks as an isolated stock, which can be divided into two bodies (North and South bodies), separated by a fine-grained granodiorite unit with a hypidiomorphic granular texture. The South body, which contains magmatic epidote, was intruded by the North body. Higher initial Sr isotope ratios of the South body, relative to the North body, indicate that sedimentary rocks were assimilated in the magma of the South body during its emplacement in the middle/upper crust. Geochemical data indicate that the Pr Fine To resulted from mixing of the magmas that produced the South body and the Pr Fine Di, with minor crustal contamination by host sedimentary rocks. Fractional crystallization of plagioclase, biotite, and hornblende in the South body resulted in the differentiation of the evolved Pr Fine Gr. In addition, Pr Fine Di has a sanukitic high-Mg andesite composition that is similar to Cretaceous high-Mg diorite bodies from the North Kyushu batholith. Overall, the results indicate that a variety of igneous processes including magma mixing, fractional crystallization, and assimilation with the host rocks, were responsible for the formation of the Ushikiri-yama granodiorite.

Magma process of the Kibe Granite (One of the Younger granitoids) in the Yanai area of the Ryoke Belt, southwest Japan 赤o 英里(Eri AKASAKI) 亀井 淳志(Atsushi KAMEI)  大和田 正明(Masaaki OWADA) Cretaceous granitic rocks in the Chugoku district, Southwest Japan arc, are divided into the following three groups; Older Ryoke granitoids, Younger Ryoke granitoids and San'yo granites. The Kibe Granite, a representative Younger Ryoke granitoids in the Yanai area, Yamaguchi Prefecture, occurs as an elliptic outcrop associated with a coeval quartz diorite, and intruded the high-grade Ryoke metamorphic rocks. The Kibe Granite is dominated by homogeneous biotite-granite that contain euhedral alkali-feldspar phenocrysts. These rocks also contain local micro-magmatic enclaves and have migmatitic structures in contact zones with the pelitic gneisses in the marginal parts of the granite. The mixing and mingling structures are developed at the contact between the granite and quartz diorite. The major and trace element variations of the Kibe Granite can be explained by a subtraction of plagioclase together with minor biotite and alkali-feldspar from a parental magma. The Kibe Granite was formed through the following processes: assimilation of the pelitic gneisses, magma mixing with the quartz diorite and fractional crystallization of a parental magma. These processes took place at the exhumation stage of the Ryoke metamorphism following its isothermal decompression path.

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Lower crustal part of the Hidaka Arc Hidaka metamorphic belt is composed of the granulite-facies unit zone and the main anatexis zone. The former can be observed on the surface, while the latter is considered to be existed beneath the Hidaka Main Thrust by the evidence of restitic Gr-Opx granulites as xenoliths included in intrusive anatectic tonalities. In pelitic granulites of zone , Bt-dehydration melting took place with forming leucosomes including euhedral Opx, An-rich Pl and Crd. Intercalated mafic granulites in zone also show the Hbl-dehydration melting and Opx-bearing leucosome formation. A small scale partial melting in zone is identified, where the produced melt would be effected to make plastic condition of lower crustal rocks and to form duplex structure in the lower crust of the Hidaka Arc. Partial molten melts derived from the main anatexis zone moved and assembled to form tonalitic magmas with peraluminous S-type and metaluminous I-type signatures, which intruded into the shallower crustal level along the floor-thrust and roof-thrust of duplex structure.