�@	Chemical characteristics of basic metamorphic rocks from the Main Zone of the Hidaka metamorphic belt, Hokkaido: an affinity to mid-ocean ridge basalts
		Subsurface temperature profiles in the Nobi Plain, central Japan
		The ilmenite-series and magnetite-series classifications of the Yanshanian granitoids of South China

Chemical characteristics of basic metamorphic rocks from the Main Zone of the Hidaka metamorphic belt, Hokkaido: an affinity to mid-ocean ridge basalts

Masumi MIKOSHIBA (UJIIE) (Geochemistry Department, GSJ)

1999

vol. 50 (10), P. 613-634

9 figs., 3 tables

Keywords: amphibolite, basic granulite, geochemistry, rare earth elements, Hidaka metamorphic belt, Hokkaido, N-type MORB

Abstract:High-grade basic, pelitic and psammitic metamorphic rocks are exposed in the western part of the Main Zone of the Hidaka metamorphic belt. Major and trace element concentrations of the basic metamorphic rocks were determined. The samples analyzed were classified into two rock types, i.e., amphibolite that is widely-exposed throughout the study area, and basic granulite which occurs exclusively along the margin of a gabbroic body in the northern part. Both show similarities in chemistry to normal mid-ocean ridge basalts (N-type MORB). Most of the amphibolites have variable and higher concentrations of Rb, Ba, K2O and Cs than typical N-type MORB, probably due to enrichment in those elements through metamorphic or alteration processes. On the other hand, the basic granulites are poorer in Rb and Th, that may have been lost during high-grade metamorphism associated with deformation. The basic metamorphic rocks originated from basalts or gabbros, of which parental magmas were derived from a mantle source depleted in light rare earth elements. Possibly, the basic magmas may have solidified at sea floor where terrigenous sediments deposited.

Subsurface temperature profiles in the Nobi Plain, central Japan

Youhei UCHIDA(Environmental Geology Department, GSJ) and Yasuo SAKURA(Department of sciences, Chiba Univercity)

1999

vol. 50 (10), P. 635-659

11 figs., 1 table, 41 appendix-figs.

Keywords: vertical temperature profile, groundwater flow system, temperature inversion, numerical analysis

Abstract:Vertical temperature profiles in the Nobi Plain are able to be classified into three types, recharge type, discharge type and intermediate type, according to the temperature gradient. Moreover, there are many temperature inversions in the vertical temperature profiles which are classified as the recharge type. These temperature inversions are manifested as the minimum temperature in the vertical temperature profile below the isothermal layer. All of the type of profiles that show the inversion are located in recharge area outside the discharge area. Annual mean surface temperature has increased about 2�� during the last 100 years in the Nobi Plain, and it is assumed that this surface warming causes subsurface temperature inversions. A numerical analysis including the effect of surface warming shows that subsurface temperatures in shallow layers are affected by changes in surface�@temperature. In the discharge area, however, temperature inversions cannot be recognized because the depth of inversion has been shifted to within 20m of the surface by upward groundwater flow, where seasonal fluctuation of subsurface temperature conceals the inversion.

The ilmenite-series and magnetite-series classifications of the Yanshanian granitoids of South China

Shunso ISHIHARA(Geological Survey of Japan) and Ping-an WANG(Chinese Academy of Geological Sciences, Beijing, China)

1999

vol. 50 (10), P. 661-670

Keywords:South China, granitoids, Yanshanian, Series I, Series II, ilmenite series, magnetite series, redox state

Abstract: Yanshanian (Jurassic-Cretaceous) granitoids of South China were evaluated in terms of the ilmenite/magnetite-series classification defined by their bulk Fe2O3/FeO ratios. Early Yanshanian granitoids are composed of 59 percent ilmenite series and 41 percent magnetite series, while Late Yanshanian granitoids consist of 43 vs. 57 percent, respectively, indicating an oxidized nature toward the younger generation. Yanshanian granitoids tend to have higher Fe2O3/FeO ratios in the Lower Yangtze region and the Southeast Maritime volcanic belt; however, no asymmetrical zoning of the ilmenite/magnetite-series distribution is observed in the main, Cathaysian folded zone of the Nanling Range, unlike Late Mesozoic granitoids occurring in the island-arc setting (e.g., Japanese Islands and Sierra Nevada-Peninsular Range batholiths). Genetic relationships of ilmenite-series granitoids with W, Sn, REE and Nb-Ta ore deposits, and magnetite-series granitoids with magnetite-hematite and Cu-Pb-Zn deposits observed in the Yanshanian granitoids of South China are consistent with the results of the Japanese Islands.