| Budget Amount *help |
¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 1990: ¥200,000 (Direct Cost: ¥200,000)
Fiscal Year 1989: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1988: ¥600,000 (Direct Cost: ¥600,000)
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| Research Abstract |
Geological survey and chemical analyses of main and minor components of Shimokawa basic rocks, Hitachi metamorphic rocks and Sanbagawa metamorphic rocks which contain altered and/or metamorphosed rocks derived from basic volcanic rocks accompanied with massive sulfide deposits were carried out. The results are summarized as follows.
1) All Shimokawa basic rocks are considered to be N-type mid-ocean ridge basalt (MORB). They have, however, larger amounts of low ion-potential LIL elements compared with the recent N-type MORB. This is explained by addition of the elements associated with the sea-floor alteration or contamination with pelitic rocks. The similar phenomena are observed in the present day sea-floor basalt from Guaymus basin, Gulf of California.
2) Hitachi metamorphic rocks contain schist and gneiss derived from acidic-intermediate-basic volcanic rocks. The geochemical properties suggest that they consist of calc-alkalic, boninitic and back-arc volcanic rocks.
3) Most of basic schists in the Sanbagawa metamorphic terrain of Kanto Mountains are N- and T-type MORB. The others are oceanic island tholeiite and alkali basalt.
4) Chemical compositions of the rock specimens from Shimokawa, Hitachi and Sanbagawa are considered to have changed sea-floor alteration or regional metamorphism. Among main and minor components of the rocks Na_2O, K_2O, CaO, Sr, Rb are relatively mobile. In contrast, FeO*, MgO, SiO _2, Nb, Ti, Y are immobile. On the basis of the relative and absolute quantity of these immobile elements, tectonic settings of altered and/or metamorphic rocs derived from volcanic rocks in geologic times are estimated.
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