Isotopic ages of rocks along the Median Tectonic Line in the Kayumi area, Mie Prefecture
Isotopic ages of rocks along the Median Tectonic Line in the Kayumi area, Mie Prefecture
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三重县香美地区中位构造线岩石的同位素年龄
DOI：
10.2465/ganko.84.75
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发表时间：
1989
期刊：
影响因子：
--
通讯作者：
A. Matsumoto
中科院分区：
文献类型：
--
作者：
H. Takagi;K. Shibata;Y. Sugiyama;S. Uchiumi;A. Matsumoto
对三重县加由米地区的中构造线（MTL）沿着的岩石进行了K-Ar、Rb-Sr和裂变径迹年龄测定。Ryoke花岗质岩石的K-Ar年龄为44.1 ~ 84.3Ma。在MTL约1000米范围内，钾长石和黑云母的年龄向MTL方向减小，可能是由与碎裂作用有关的热液蚀变引起的，而人闪长岩的年龄向MTL方向增大。根据K-Ar年龄和矿物闭合温度计算的花岗岩冷却速率为31-56°C/Ma。三坝川带泥质片岩中白云母的K-Ar年龄为73.6- 75.6Ma;即使在MTL附近也没有观察到年龄的减小。白云母的Rb-Sr年龄为72.2- 77.5Ma，与K-Ar年龄基本一致。这些年龄数据被假定为指示该地区的三坝川片岩的最高温度的时间。锆石的裂变径迹年龄为52.4 ~ 59.5Ma，与同类岩石的钾长石K-Ar年龄相近。三坝川片岩中锆石的裂变径迹年龄分别为59.0和61.2Ma，比白云母的K-Ar年龄年轻近15 Ma。从西谷川和香见的MTL断层泥中分离出的细颗粒（<2μm）的K-Ar年龄分别为41.8Ma和51.4Ma。前者可能代表了与碎裂作用相关的MTL主要断层运动之后的热液蚀变时间。
K-Ar, Rb-Sr and fission-track age determinations were carried out on rocks along the Median Tectonic Line (MTL) in the Kayumi area, Mie Prefecture. K-Ar ages on the Ryoke granitic rocks range from 44.1 to 84.3 Ma. Within about 1000m of MTL, the ages for K-feldspars and biotites decrease toward MTL, probably caused by the hydrothermal alteration associated with cataclasis, whereas the ages for homblendes increase toward MTL. The cooling rate of the granitic rocks, calculated from K-Ar ages and closure temperatures of minerals, is 31-56°C/Ma. K-Ar ages for muscovites from pelitic schists in the Sanbagawa belt are 73.6-75.6 Ma; decrease in age is not observed even near MTL. Rb-Sr ages for muscovites from the schists are 72.2-77.5 Ma, nearly the same as the K-Ar ages. These age data are assumed to indicate the time of maximum temperature for the Sanbagawa schists in this area. Fission track ages for zircons from the Ryoke granitic rocks range from 52.4 to 59.5 Ma, approximating to K-Ar ages of K-feldspars for the same rocks. Fission-track ages for zircons from the Sanbagawa schists are 59.0 and 61.2 Ma, nearly 15 Ma younger than the K-Ar ages of muscovite for the same rocks. The fine fractions (<2μm) separated from MTL fault gouges at the Nishitani River and Kayumi give K-Ar ages of 41.8 and 51.4 Ma, respectively. The former age probably represents the time of hydrothermal alteration following the major fault movement of MTL associated with cataclasis.