Muscovite K-Ar ages of the Sanbagawa schists, Japan and argon depletion during cooling and deformation
Muscovite K-Ar ages of the Sanbagawa schists, Japan and argon depletion during cooling and deformation
复制标题
日本三波川片岩的白云母 K-Ar 年龄以及冷却和变形过程中的缺氩
DOI：
10.1007/bf00379739
复制
发表时间：
1988
影响因子：
3.5
通讯作者：
H. Takasugi
中科院分区：
文献类型：
--
作者：
T. Itaya;H. Takasugi
用K-Ar法测定了四国中部三八川地片岩中70个白云母的年代。白云母年龄随变质等级的增加而逐渐变老。在同一带内，变形更为严重的片岩年龄明显更小。这些K-Ar年龄的变化可能是由于变形过程中系统的氩耗尽，即在隆升和冷却期间形成大规模平卧褶皱的韧性变形期间白云母的动态再结晶。在变形范围更广的片岩中，低温变形时间较长的低品位片岩中，氩气损失较大。泥质片岩年龄与粒度的关系表明，粗粒白云母比细粒白云母损失更多的氩。在主要走滑断层（如中构造线）附近和逆冲断层附近没有明显的年龄重置。年代学和地质资料的结合限制了日本国中部少长-黑云母带三巴川片岩的冷却速率为9-12°C/Ma。
Seventy muscovites from schists in the Sanbagawa terrain in central Shikoku were dated by the K-Ar method. The muscovite ages are consistently older with increasing metamorphic grade. Within the same zone the ages are significantly younger in schists which have been more severely deformed. These K-Ar age variations could be due to systematic argon depletion during deformation i.e., to the dynamic recrystallization of muscovites during ductile deformation that formed a large-scale recumbent fold during the uplift and cooling. Argon loss was greater in schists that were more extensively deformed and in the lower grade zone that experienced a longer period of low-temperature deformation than the higher grade zone. The relationships between age and grain size in a pelitic schist suggest that coarse-grained muscovites lost more argon than the finegrained ones. There was no significant resetting of ages in the vicinity of major strike-slip faults, such as the Median Tecotonic Line or near thrust faults. The combination of geochronological and geological data constrains the cooling rate of the Sanbagawa schists to 9–12° C/Ma in the oligoclase-biotite zone in central Shikoku, Japan.