It is well known that the distribution of the heights of marine terraces shows the late Quaternary crustal movements. The information for crustal movements during the Quaternary is also obtained from the heights of summit planes on hills, the geologic structure of Neogene formations and the geodetic data. The east coast of Matsumae Peninsula was investigated to clarify the type, amount and rate of Quaternary crustal movements through the distribution of the heights of marine terraces and summit planes on hills, the geologic structure of Neogene formations and the geodetic data. The geomorphological and geological studies in this region permit the following conclusions. 1) The whole region tends to uplift during the Quaternary; the amount of uplift during whole Quaternary is about 250-300m on both the Kamiiso Uplift Block and Matsumae Uplift Block, about 200m in Kikonai Sedimentary Province. 2) The folding with 3 km of wave length and the local semi-doming have been continuously active in the east part of this region after terraces were formed. The center of uplift has also moved eastward during the late Pleistocene. 3) The geologic faults and new faults which run on the eastside of the Kikonai Fault at the eastern border of the Esashi Uplift Block and the Ohirakawa Fault at the western border of the Kamiiso Uplift Block have been rather active after the middle Pleistocene. Assuming the ages of marine terraces, summit planes on hills and Neogene formations, it seems that the rate of uplift has increased after the summit planes on hills were formed.
Triangular diagrams showing the trends and fields of the ratios of V, Ni and Co in some igneous rock types, oceanic tholeiites and rock-forming minerals are presented and their significance is discussed. Typical igneous rock types and rock-forming minerals occupy characteristic fields in the diagrams. It is clear that there are different trends for the ratios of V, Ni and Co and V/(V+Ni+Co) ratios to Si contents among various differentiation series. It seems that such diagrams are suitable for showing chemical variation in geochemical process.
Boninite, first described by KIKUCHI (1888, 1889) and named by PETERSEN (1891) in Chichi-jima of the Bonin Islands, recently gained a profound petrogenetic significance after about eighty years' missing. Its re-appraisal was accompanied by the discovery of some boninite localities in the western Pacific island arcs and ophiolites. Among them of particular interest in relation to ophiolites is clinoenstatite-bearing boninite discovered by SAMESHIMA et al.(1983) near Nepoui on the west coast of New Caledonia, because numerous, huge masses of ophiolites are exposed on New Caledonia.During a short trip to New Caledonia, we also found a new occurrence of boninite pillow lavas near Col d'Amieu in the central part of the island. While the Népoui boninite is possibly a member of the “Formation des Basaltes” of late Cretaceous to Eocene age, the Col d'Amieu boninite occurs in the weakly metamorphosed pre-Senonian rocks. Close inspection of the literature reveals that there are several other boninite localities associated with island arc tholeiites and/or mid-ocean ridge basalts in the New Caledonia ophiolites. In Népoui, an MgO- and SiO2-rich, hypabyssal rock crystallizing quartz and feldspar and a cumulate olivine orthopyroxenite were found together with the glassy clinoenstatite boninite breccias, accompanying a mylonitized serpentinite sheet. Both the hypabyssal rock and the clinoenstatite boninite are characterized by very low CaO content and Ca/Al ratio, suggesting that they have been derived from the same boninite magma. Proto-and ortho-pyroxenes from the Nepoui boninite are lower in Ca at a given ‘Mg’ value than those from the Bonin Island boninites, and the Népoui pigeonites and augites are less magnesian, indicating their later crystallization. In contrast, the Col d'Amieu boninite has early formed augites with high ‘Mg’ and Cr, owing to its high bulk rock CaO content. The crystallization stage of pigeonite like augite appears to depend on CaO content in the host rock. Mg-rich augites from boninites are generally poor in Al, in agreement with the low Al/Si ratio of boninites, but the Al in augite increases rapidly with decreasing‘Mg’, which reflects the effective quenching and no crystallization of plagioclase in boninites.Chromite compositions of the two New Caledonia boninites are similar; both have very high Cr content and Cr/Al ratio, a feature characteristic of boninite chromites. The boninite primary magmas show a considerably wide range of CaO contents. The Col d'Amieu boninite, as well as boninites with augite phenocrysts from the Bonins, represents the most CaO-rich end. The Ca/Al ratio in the boninite primary magmas decreases in order of Col d'Amieu, Bonin, Papua, Sanukitoid and Népoui. In New Caledonia, various types of boninite, in terms of chemistry, mineralogy, texture, age and tectonic setting, may occur in close association with island arc tholeiites and midocean ridge basalts. New Caledonia would be the most favorable place for boninite studies.