Two new geochemical reference samples, basalt JB‐1b and coal fly ash JCFA‐1 have been prepared by the Geological Survey of Japan (GSJ) for collaborative studies on their chemical composition. Provisional values for twenty nine major, minor and trace elements are presented. The homogeneity tests showed that all elements studied can be considered to be homogeneously distributed. A description of their geological and mineralogical characteristics is also given.

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Small-volume plutons of Early to Late Cretaceous ages are widely distributed in the Yamizo Mountains, central Japan. These plutons consist predominantly of granitoids, classified into hornblende gabbro, quartz diorite, hornblende-biotite granodiorite and coarse-grained biotite granite. The quartz diorite (52-64 wt% of SiO 2 ) is characterized by a high Sr content (606-769 p.p.m.) associated with a low Y (13-27 p.p.m.) and heavy rare earth element content (Yb content of 1.19-2.13 p.p.m.). On the Sr/Y versus Y diagram, this rock type mainly plots in the adakite and Archean high-Al tonalite, trondhjemite and granodiorite (TTG) field. Together with its initial Sr isotopic ratios, which range from 0.7038 to 0.7046, these data suggest that quartz diorite originated as slab melts. However, geochemical calculations assuming either eclogite or garnet amphibolite as the source material do not support this suggestion. Instead, the chemical compositions of quartz diorite are better explained by the fractional crystallization of hornblende, plagioclase and biotite from a primitive, basaltic melt in a magma chamber. In this case, the formation of the associated hornblende gabbro can also be explained by the accumulation of hornblende and plagioclase. Adakitic rocks of Early Cretaceous ages have also been reported in the Tamba Belt of the inner zone of southwest Japan, located ca 500 km west of the Yamizo Mountains. These rocks can be correlated to the adakitic rocks in the Yamizo Mountains based on the geology, petrography, geochemistry and radiometric ages. Therefore, we propose the possibility that the Early Cretaceous adakitic rocks in the inner zone of southwest Japan were produced by fractional crystallization from basaltic arc magmas generated by a partial melting of metasomatized wedge mantle peridotite.

The Chilas Igneous Complex is one of the major geologic units in the Kohistan terrane of the Himalaya of northern Pakistan. The Kohistan terrane is regarded as a tilted island-arc sequence. The Chilas Complex is a 300-km-long, 40-km-wide plutonic body that intrudes the Kamila Amphibolite. The Main facies rocks of the Chilas Complex consist of gabbronorite, diorite, and quartz diorite. Small bodies of ultramafic-mafic association composed mainly of peridotitic-gabbroic cumulates, and a layered gabbronorite body, are also present, probably as xenoliths. A few samples are considered to have been contaminated as a result of assimilation of xenolithic materials and country rocks: Excluding them, 14 whole-rock samples of the Main facies have an Rb-Sr age of 111 ± 24 Ma and an initial 87 Sr/ 86 Sr ratio of 0.70403 ± 0.00006. Gabbroic rocks from the ultramafic-mafic association, from the layered gabbronorite body, and from mafic dikes, have 87 Sr/ 86 Sr ratios between 0.7039 and 0.7044, interpreted to be close to the 87 Sr/ 86 Sr ratios at the time of their generation. The whole-rock isochron age for the Main facies is regarded as the age of intrusion. The initial 87 Sr/ 86 Sr ratio for the Main facies is within the range of typical arc magmas, suggesting that the igneous activity occurred within an island arc or orogenic belt close to a continental margin. The age of intrusion of the Chilas Complex is similar to that of the earliest magmatism in the Kohistan batholith and to the Cretaceous plutonism in Ladakh and Karakorum, indicating large-scale generation of subduction-related magmas in the western Himalayan region and Karakorum during the mid-Cretaceous.