形成闽浙火山岩带的洋陆转换作用

The ocean—continent transition process on formation of Zhejiang—Fujian volcanic rock belt

本文研究了闽浙火山岩带形成的洋陆转换作用。洋陆转换作用涉及整个上地幔物质运动,研究的主要根据来自对地幔调查的地球物理资料。研究表明,闽浙火山岩带形成的根源在其下方的伊佐奈崎板块,它反映为上地幔底部的高波速异常体。它向上方释放基性的熔体,使软流圈底部变为玄武质低黏度物质,并且向上继续蠕动。向上的继续蠕动在岩石圈地幔形成英安质岩浆房。由于闽浙地壳比较冷硬的克拉通性质,英安质岩浆房上涌速度缓慢,混染了大量上地壳物质,转变成为酸性的枝叉状岩浆囊。在125 Ma太平洋板块发生旋转后,由于地壳逐渐放松俯冲造成的挤压,岩浆释放造成大规模酸性火山爆发,形成闽浙火山岩带。可见,大陆增生的主要方式不仅有俯冲带大量英安质和玄武质幔源岩浆上涌的模式,还有混染了大量上地壳物质的流纹质岩浆活动。

In this paper, the formation of volcanic rock belts in Fujian and Zhejiang is studied on the ocean—continent transition process. The ocean—continent transition involves the entire upper mantle material movement, and the study is mainly based on geophysical survey’s data. Studies have shown that the root of the formation of the Fujian and Zhejiang volcanic belt was the Izanaqi Plate below it, which is reflected as a high seismic velocity anomaly at the bottom of the upper mantle. It releases basic melts upwards, turning the bottom of the asthenosphere into a basalt like low-viscosity substances and continuing to creep upwards. Upward continued creeping in the lithosphere mantle formed the andesite magma chambers. Due to the relatively cold and hard craton nature of the crust of Fujian and Zhejiang, the upwelling rate of the magma was slow, mixed with a large amount of upper crust material, and transformed into an acidic branch-like magma sac. After the rotation of the Pacific Plate after 125 Ma, because the Earth’s crust was no longer subjected to compression caused by the subduction, the magma released and caused a large-scale acid volcanic eruptions, forming the Fujian—Zhejiang volcanic rock belt. It can be seen that the main ways of continental accresion are not only fillow the pattern of upwelling of andesite and basalt magmas in the subduction zones, but also had the rhyolite magmatic activities.