SUMMAR YThe Setouchi volcanic belt in SW Japan is characterized by the occurrence of andesites with an unusually high Mg concentration (high-Mg andesites, HMAs). Such HMAs may have formed under unusual tectonic settings, as basaltic magmas are produced dominantly in the mantle wedge of modern subduction zones. A total of 50 new K±Ar ages for the Setouchi rocks con®rmed that intermediate to felsic magmatism including the eruption of HMAs took place in this volcanic belt within a short period of 13.2t0.4 Ma. This is synchronous with the clockwise rotation of the SW Japan arc sliver that was associated with the opening of the Japan Sea back-arc basin. Such rotation of an arc sliver forced the initiation of subduction and partial melting of a young and hot lithosphere of the Shikoku Basin beneath the arc. Interaction between slab melts and mantle wedge peridotites may be a possible generation process of unusual HMA magmas. When the SW Japan arc sliver ceased to drift, the Setouchi magmatism was switched off by the cessation of subduction. The eruption of HMA magmas may also be attributed to an extensional stress ®eld in the Setouchi region, in contrast to the compressional stress regime documented for other regions of the SW Japan arc.

In an attempt to find out a new molecular counterpart of CCN family protein 2 (CCN2), a matricellular protein with multiple functions, we performed an interactome analysis and found fibroblast growth factor (FGF) -1 as one of the candidates. Solid-phase binding assay indicated specific binding between CCN2 and FGF-1. This binding was also confirmed by surface plasmon resonance (SPR) analysis that revealed a dissociation constant (Kd) of 3.98 nM indicating strong molecular interaction between the two. RNA analysis suggested that both FGF-1 and CCN2 could be produced by chondrocytes and thus their interaction in the cartilage is possible. These findings for the first time indicate the direct interaction of CCN2 and FGF-1 and suggest the co-presence of these molecules in the cartilage microenvironment. CCN2 is a well-known promoter of cartilage development and regeneration, whereas the physiological and pathological role of FGF-1 in cartilage mostly remains unclear. Biological role of FGF-1 itself in cartilage is also suspected.

A new mineral standard for K-Ar dating, SORI93 biotite, has been prepared from the Sori Granodior ite in Gunma Prefecture, Japan. This is intended as a substitute of the existing standard, SORI biotite, which is well calibrated against international standards. The K20 and radiogenic 40Ar contents for SORI93 biotite have been determined to be 8.16 ± 0.04 (1a) wt % and (25.0 ± 0.1) x 10-6 (la) cm3STP/g, re spectively. The calculated K-Ar age is 92.6 ± 0.6 Ma, which is about I million years older than that of SORI biotite. Chloritization up to 10% partly occur along cleavages of SORI93 biotite. In order to certify the homogeneity, K20 contents have been repeatedly analyzed for 100, 50, 20 and 10 mg aliquots. The analytical result of 100 mg SORI93 biotite shows a relative standard deviation similar to that of SORI biotite and the geochemical standards, JG-1 and JB-1. The standard deviations of aliquots less than 100 mg are about twice those of the three standards. This inhomogeneity may be caused by the presence of partially chloritized biotite. It is suggested to use 100 mg to ensure the homogeneity of subsamples.