Temporal and apatial variations of the Cenozoic volcanic rocks from the Notrheast Japan

日本东北部新生代火山岩的时空变化

基本信息

批准号：
03302022
负责人：
SHUTO Kenji
金额：
$ 6.91万
依托单位：
Niigata University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Co-operative Research (A)
财政年份：
1991
资助国家：
日本
起止时间：
1991 至 1993
项目状态：
已结题

项目摘要

The results obtained from this research project are summarized as follows.1) The excellent petrological investigations have been made for numerous Cenozoic volcanic rocks from various localities in the Kyushu, Chugoku Hokuriku, northern Kanto, Tohoku and southwestern and northeastern Hokkaido discricts. Basaltic rocks dredged from the Okushiri Ridge, off western Hokkaido were also described prtographically. These petrological data may play an important role in revealing not only the origin of these volcanic rocks from each field but also the tectonic events around the circum Japan Sea region.2) K-Ar age determination has been carried out for many Tertiary volcanic rocks, especially those from the Northeast Japan arc. Our new data and the available rediometric age data for the Tertiary volcanic rocks provided by many previous workers have made it possible to distinguish the three different volcanic fronts in the NE Japan arc in temporal and spacial distribution.3) Based on Sr and Nd iso … More topic data for Tertiary and Quaternary basaltic rocks from the NE and SW Japan arcs, relationships are discussed between the temporal variation on magma source characteristics and the opening of the Japan Sea back-arc basin. Basaltic rocks from the back-arc side of the NE Japan arc during 35 0 Ma can be divided into two different groups with respect to initial Sr isotopic ratios, initial epsilonNd values and ages. One is characterized by higher Sri ratios (0.7040-0.7058) and lower epsilonNd values (0-+3) and the other by lower Sri ratios (0.7029-0.7040) and higher epsilonNd values (+3-+8). The former basaltic activity has taken place continuously during 30-10 Ma, whereas the latter activity occurred mainly in two periods ; i.e. ; at around 34-35 Ma and after 15 Ma. Similar evidences are also observed in basaltic rocks from the transitional zone to the back-arc side where basaltic activity characterized by higher Sri ratios took place continuously during 15-0 Ma, whereas that by lower Sri ratios occurred at around 15 Ma and after 3 Ma. These evidences suggest that the sub-continental mantle beneath the NE Japan arc may have constructed layred structure ; upper isotopically enriched (Sri=0.7040-0.7058, epsilonNd=0-+3) and lower depleted (Sri=0.7029-0.7040, epsilonNd=+3-+8) layrs. Basaltic magmas with enriched isotopic nature are considered to have been formed from the upper layr, while those with depleted isotopic one from the lower layr. Less

从该研究项目中获得的结果总结如下。1）对来自九州，Chugoku Hokuriku，Kanto，Kanto，Tohoku，Tohoku，Toohoku和Southwestern和Northeastern和Northeastern和Northeastern Hokkaido Incrics的众多新生代火山岩进行了出色的岩石学研究。从Okushiri山脊挖出的玄武岩岩石也在北海道旁边描述了。这些岩石学数据不仅在揭示每个田地的这些火山岩的起源，而且还起着重要的作用。我们的新数据以及许多以前的工人提供的第三纪火山岩的可用重新计量年龄数据使得在日本NE日本的三个不同的火山阵线区分临时和空间分布是基于SR和ND ISO的三个不同的火山界。海面弧盆地。相对于初始SR同位素比，初始epsilonnd值和年龄，可以将日本NE日本弧的后弧的玄武岩岩石分为两组。一个特征在于SRI比（0.7040-0.7058）和较低的Epsilonnd值（0-+3），另一个则为SRI比（0.7029-0.7040）和较高的Epsilonnd值（+3-+8）。前者的基本活动在30-10 MA期间连续进行，而后一种活动主要发生在两个时期。 IE。 ;在大约34-35 MA和15 MA之后。在从过渡区到后弧侧的玄武岩岩石中也观察到了类似的证据，在15-0 mA期间，以较高的SRI比的特征进行了玄武岩活性，而SRI比率较低的SRI比发生在15 mA左右和3 Ma之后。这些证据表明，日本新弧下的次大陆地幔可能已经建立了铺设结构。同位素上部富集（SRI = 0.7040-0.7058，epsilonnd = 0-+3）和下depthd（SRI = 0.7029-0.7040，epsilonnd =+3-+8）layrs。具有富集同位素性质的玄武岩岩浆被认为是由上层形成的，而那些具有耗尽的同位素的岩浆是从下层中形成的。较少的