[S-IT20] New perspectives on accretion and exhumation processes during oblique plate convergence

[SIT20-P01] Evidence for active subduction zone fluid flow recorded in antigorite serpentinites in the high-P metamorphic Yuli Belt, eastern Taiwan

*Ilona Sakaguchi¹、Yui Kouketsu²、Dominikus Deka Dewangga³、Chin-Ho Tsai³、Katsuyoshi Michibayashi² (1.International Professional University of Technology in Nagoya、2.Nagoya University、3.National Dong Hwa University)

キーワード：antigorite serpentinite, Yuli belt, subduction zone fluid flow

The fluids released by serpentinite dehydration reactions play an important role in many subduction zone processes, such as in elemental cycling, melt formation and in causing seismicity inducing hydrofracturing in the subduction zone. In this study, we analyzed various microstructures and compositional variation of three antigorite serpentinite bodies located in the Yuli Belt in order to study the nature of fluid flow in the subduction channel. Yuli belt is a high pressure metamorphic belt in eastern Taiwan that is part of the Tananao Metamorphic Complex, a subduction complex which formed during the subduction of the South China Sea plate. The microstructure and mineral assemblage of the serpentinite samples werestudied using optical microscopy, attenuated total reflection infrared spectroscopy (ATR-IR) and Raman spectroscopy,and the composition of the samples was measured by electron microprobe analyzer (EPMA). Based on these analyses, we found that the Yuli belt serpentinites were subjected to active fluid flow during subduction. Measurements from different alteration zones and veins showed that antigorite was recrystallized by several pulses of fluid flow. Especially the Fe content of antigorites tended to vary between vein and matrix antigorites. In addition, metamorphic olivine observed in the Chinshuichi area is a sign of partial dehydration of the serpentinites during subduction. Furthermore, various types of different alteration zones, such as albite-rich contact zones and chlorite and amphibole rich shear zones, as well as rodingite and talc veins observed in and around the serpentinites, showed that the serpentinite rocks were further metasomatized by fluids with varying compositions. Overall, compositional and microstructural evidence from the Yuli belt serpentinites seem to indicate active subduction channel fluid flow in the Tananao Metamorphic Complex.