Geochemical Studies on Basic Rocks Accompanied with Massive Sulfide Deposits

Research Project

Project/Area Number	63540656
Research Category	Grant-in-Aid for General Scientific Research (C)
Allocation Type	Single-year Grants
Research Field	鉱物学(含岩石・鉱床学)
Research Institution	Waseda University
Principal Investigator	MARIKO Tadashi Waseda University, School of Education, Professor, 教育学部, 教授 (00063454)
Co-Investigator(Kenkyū-buntansha)	OGASAWARA Yoshihide Waseda University, School of Education, Assistant Professor, 教育学部, 助教授 (70160736)
Project Period (FY)	1988 – 1990
Project Status	Completed (Fiscal Year 1990)
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)
Keywords	Meta volcanics / Mid-ocean ridge basalt / Calc-alkali rocks / Boninite / Back-arc basalt / Oceanic island alkali basal / Oceanic island tholeiite / Massive sulfide deposits / 三波川変成岩 / 別子型鉱床 / 塩基性片岩 / 海嶺型玄武岩 / 海洋島型ソレアイト / 海洋島型アルカリ玄武岩 / 下川塩基性岩 / 日立変成岩 / 島孤型火山岩 / 縁海 / 海嶺ソレアイト / 単斜輝石の化学組成 / 全岩組成
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.