System dynamics in a subduction zone

俯冲作用是深海流体向壳幔循环的主要过程。作为孔隙流体或大洋地壳或上覆沉积物的含水矿物中捕获的流体在早期俯冲期间释放。释放的流体主要通过增生复合体，并对增生复合体产生物理和化学作用。结果如下。(1)浅部（<10 km）的氧同位素比值受流体影响不大。(2)在增生杂岩的中部（10- 15 km），流体通过剪切带，引起剪切带附近的物质迁移，如层序外逆冲断层。(3)在增生杂岩的深部，脱水释放的流体沿沿着岩性边界通过，并产生区域性的氧同位素蚀变。(4)泥质岩和基性岩的氧同位素比值在增生杂岩的中部最大。另一方面，钙质岩的氧同位素比值随深度的增加而减小。(5)在浅部增生杂岩中，同位素蚀变域的大小小于一个手掌大小，而在深部增生杂岩中，同位素蚀变域是一个可填图级。

A subduction is a main process for the circulation of fluids from deep sea to crust and mantle. The fluids trapped as pore fluids or in hydrous minerals of oceanic crust or overlying sediments are released during an early subduction. Released fluids mostly pass through the accretionary complex and have physical and chemical effects upon it.In this research project, we have succeeded in elucidating a series of mass transfer by fluids. The results are as follows.(1) Oxygen isotope ratios of shallow parts of the accretionary complex (<10km depth) are not greatly influenced by fluids.(2) In medium parts of accretionaly complex (10-15km depth), fluids pass through shear zones and give rise to mass transfer of the vicinity of shear zones such as out-of-sequence thrusts.(3) In deep part of accretionaly complex, fluid released by dehydration pass through along the lithological boundaries and regionally give oxygen isotopic alterations.(4) Oxygen isotopic ratios of pelitic and basic rocks are the largest in medium parts of the accretionary complex. On the other hand, oxygen isotopic ratios of calcareous rocks decreases with increasing depth.(5) In shallow accretionary complex, domains of isotopic alterations are smaller than a size of hand speciman, whereas in deep one, those are a mappable order.