Temporal and spacial geochemical variation in the Neogene volcanic rocks and the dource mantle in NE Honshu arc

本州岛弧东北缘的新生代剖面研究最为完整。在这一段，有三个火山期；大陆边缘火山期、弧后盆地火山期和岛弧火山期。在大陆边缘火山期和岛弧火山期，地幔楔内1320个地幔柱的热含量单调地深至弧后侧。大陆边缘火山期等温线的倾斜较岛弧火山期平缓。大陆边缘火山期火山锋岩浆分离深度远高于岛弧火山期。另一方面，弧后盆地火山期地幔温度在弧后侧最高。岛弧火山期火山岩过程识别图清楚地表明了火山前、弧后两侧地幔非均质性的存在。两个源幔在矿物学上可能是非均质的，且呈垂直层状。岩浆温度的非均质性和跨弧剖面与具有局部低速区的地震速度结构密切相关。第四纪火山作用表现为短期和长期向弧后侧扩张。这种喷发阵在时间-空间分布图上通常从火山前缘开始，依次向弧后扩散。岩浆同时通过构造脉冲从深层储层转移可能是同步火山活动的一个原因。在东北本州弧南部第四纪，存在与构造运动同步的5 ~ 10万年的周期性岩浆喷发事件。气候爆发似乎与地球绕太阳轨道的离心率最大值的时间相吻合。潮汐力可以作为俯冲板块压应力的补充。

The NE Honshu arc has the most completely studied Cenozoic section. In this section, there are three volcanic periods ; continental margin volcanic period, back-arc basin volcanic period, and issland arc volcanic period. The 1320ﾟC iotherm in the mantle wedge is monotonously deep to the back-arc side at the continental margin volcanic period and the island arc volcanic period. The inclination of the isotherm in the continental margin volcanic period is more gentle than in the island arc volcanic period. The magma segregation depth at the volcanic front was much deeper in the continental margin volcanic period than in the island arc volcanic period. On the other hand, the mantle temperature was the highest at the back-arc side in the back-arc basin volcanic period.The presence of mantle heterogeneity between the volcanic front side and the back-arc side was clearly shown in the process identification diagrams for the volcanic rocks of the island arc volcanic period. The two source mantles can be mineralogically heterogeneous, and vertically layred. The heterogeneity and across-arc profile of magmatic temperatures are closely related to the seismic velocity structure with the localized low-velocity regions.The Quaternary volcanism shows short-term and long-term spreading to back arc side. This eruption arrays in a temporal-spatial plot have usually commenced at the volcanic front, and propagated to the back-arc sequentially. Simultaneous magma transfer from the deeper reservoirs by tectonic pulse could be a cause of the synchronized volcanic activity. Through the Quaternary age in the southern part of the NE Honshu arc, the periodic magma eruption episodes at intervals of 50 to 100 thousand years synchronized with tectonic movements exists. The climactic eruptions seems to match the timing of the eccentricity-maximums of the Earth's orbit around the Sun. The tidal forces could work supplementary to the compressive stress from subducting plate.