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1引言在西南日本(当时它是东亚大陆边缘的一部分)自晚白垩世至早第三纪显著地发生了活跃的岩浆作用。这些时期的火成岩沿中央构造线以NEE-SWW至NE-SW方向广泛分布(图1)。为了研究这次岩浆活动的机制已进行了许多地质学、岩石学或年代学的研究(Mara-kami,1979;Hayama,1982a,b)。关于西南日本内的岩浆作用的可靠资料已收集到,但它的机制还没有清楚解释。Uyeda和Miyashiro(1974)首先指出,白垩纪岩浆作用是因脊的下潜而发生的,因为此岩浆作用的分布面积大大地大于仅由简单俯冲引起的。Kinoshita等(1986,1988)主要根据年代提出了西南日本岩浆作用的新的动力学模式。然而,关于矿物年代和岩体冷却史之间关系的一些问题还是一个留待讨论的课题。 本文中,对西南日本花岗岩体年代详细地作了再检查,并还考虑了岩体的冷却史。所采用的年代资料是仅用一种方法(黑云母K-Ar年代法)并从具有小于50％大气~(40)Ar的未蚀变岩石样品中选出的。然后,我提出了岩浆作用迁移概念和与脊俯冲有关的某些现象。这个概念还被应用于中生代岩浆作用,这岩浆作用沿东亚大陆边缘向东北延伸了7000km以上。
1 INTRODUCTION Significantly active magmatism took place in Southwestern Japan (at the time it was part of the margin of the East Asian continent) from Late Cretaceous to early Tertiary. The igneous rocks in these periods are widely distributed along the central tectonic line in the NEE-SWW to NE-SW directions (Figure 1). Much of geology, petrology or chronology has been studied in order to study the mechanism of this magmatic activity (Mara-kami, 1979; Hayama, 1982a, b). Reliable information has been collected on the magmatism in Southwest Japan, but its mechanism is not yet clearly articulated. Uyeda and Miyashiro (1974) first pointed out that the Cretaceous magmatism occurred due to the dips of the ridge, because the magmatic distribution was much larger than simply by simple subduction. Kinoshita et al. (1986, 1988) proposed a new kinetic model of magmatic activity in southwestern Japan mainly based on years. However, some questions about the relationship between the age of minerals and the cooling history of rock mass are still a subject to be discussed. In this paper, we re-examine the age of the granites in southwestern Japan in detail and also consider the cooling history of the rock mass. The chronological data used were selected from only one method (biotite K-Ar dating) and from unmodified rock samples with less than 50% air (40) Ar. Then, I proposed the concept of magmatic migration and some phenomena related to ridges and subduction. This concept has also been applied to Mesozoic magmatism, which extends over 7000 km to the northeast along the margin of the East Asian continent.