1989 Fiscal Year Final Research Report Summary
Petrogenetic study on granitoids based on Sr,Nd and Pb isotopes.
| Project/Area Number |
63540609
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
地質学一般
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| Research Institution | Shimane University |
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Principal Investigator |
IIZUMI Shigeru Shimane Univ., Fac. of Sci., Professor., 理学部, 教授 (80032639)
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| Co-Investigator(Kenkyū-buntansha) |
YAMAGUCHI Yoshiaki Shimane Univ., Fac. of Sci., Associate Professor., 理学部, 助教授 (50144689)
MIYAKE Yasuyuki Shimane Univ., Fac. of Sci., Associate Professor., 理学部, 助教授 (70200144)
SAWADA Yoshihiro Shimane Univ., Fac. of Sci., Associate Professor., 理学部, 助教授 (80196328)
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| Project Period (FY) |
1988 – 1989
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| Keywords | Granite / Inner Zone of SW Japan / Cretaceous / Sr / Nd / Isotope |
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| Research Abstract |
On the basis of petrography, petrochemistry and Sr and Nd isotopes, Jurassic to Miocene granitoids in southwest Japan are petrogenetically examined.
1)Rb-Sr isotope ages were determined for a amphibolite and two gneissose tonalites which were newly found in the western skirts of Mt. Daisen, San-in area, southwest Japan. The amphibolite shows a Rb-Sr whole rock-mineral isochron age of 185 Ma, and the tonalites have younger whole rock-mineral isochron ages. The tonalites must have had ages around 180 Ma, but would have been completely or partially recrystallized by intrusion of Cretaceous granitoids. Then these rocks should be correlated to those in the Hida Metamorphic Zone in central Japan.
2) Cretaceous to Paleogene granitoids in the Inner Zone of Southwest Japan have variable initial Sr and Nd isotope ratios. Granitoids in San-in Zone have usually low Sr and high Nd isotope ratios, whereas those in San-yo and Setouchi Zones have higher Sr and lower Nd isotope ratios. Basic rocks in the Ryoke Zone are Paleozoic in age, and have high Sr and low Nd isotope rations corresponding to those in San-yo and Ryoke Zones. It has been suggested that the Paleo-Ryoke continent, a micro continent, was situated along the southern margin of the present Ryoke Zone. The greatest part of the micro-continent may have been underthrusted beneath the Chugoku District during the Cretaceous, and the underthrusted micro-continent would have been the main magma source for the Cretaceous granitoids in San-yo and Ryoke Zones.
3) The magmas for the Asizuri Pluton in the Outer Zone must have been yielded from upper mantle, lower and middle crust.
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Research Products
(12 results)
