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Petrogenetic study on granitoids based on Sr,Nd and Pb isotopes.

基于Sr、Nd、Pb同位素的花岗岩岩石成因研究。

基本信息

批准号：
63540609
负责人：
IIZUMI Shigeru
金额：
$ 1.15万
依托单位：
Shimane University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1988
资助国家：
日本
起止时间：
1988 至 1989
项目状态：
已结题

项目摘要

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.

在岩相学、岩石化学和锶、钕同位素的基础上，对日本西南部侏罗纪至中新世花岗岩类进行了岩石成因研究。1)测定了新发现的一块角闪岩和两块片麻状英云闪长岩的Rb-Sr同位素年龄。日本西南部山仁地区的大仙。角闪岩Rb-Sr全岩-矿物等时线年龄为185 Ma，英云闪长岩具有较年轻的全岩-矿物等时线年龄。英云闪长岩的年龄一定在180 Ma左右，但可能被白垩纪花岗岩类侵入而完全或部分重结晶。2)日本西南部内区白垩纪至古近纪花岗岩具有不同的初始锶、钕同位素比值。三因带的花岗岩类通常具有低的锶和高的Nd同位素比值，而三约和色头池带的花岗岩类具有较高的锶和较低的Nd同位素比值。Ryoke带的基性岩时代为古生代，与三洋和Ryoke带的基性岩具有较高的锶和低的Nd同位素比值。有人认为，古Ryoke大陆是一块微大陆，位于现今Ryoke带的南缘。微大陆的最大部分可能在白垩纪被冲到初谷地区之下，冲断的微大陆可能是三洋和琉球地区白垩纪花岗岩类的主要岩浆来源。3)外带Asizuri岩体的岩浆肯定来自上地幔、下地壳和中地壳。