09:00 〜 11:00
[SIT20-P05] Ductile deformation structures in subduction channel: SP within the mélange in Chingshui creek in Taiwan HP Yuli belt
キーワード：ductile deformation, Porphyroblasts, Chingshui creek, HP Yuli belt, Taiwan, subduction channel
Based mainly on the field geological investigation, combined with previous geochemical and geochronological data, we characterize the deformation structures, particularly the multiple set of metamorphic deformation fabrics, surrounding the abundant serpentinite blocks in the pelitic schist. We use the Yuli Belt in eastern Taiwan as a study case to illustrate the idea that mafic/ultramafic bodies (e.g., serpentinite) within the pelitic mélange in the subduction channel acted as porphyroblasts in the highly shear zone.
During the continental subduction within the subduction channel, serpentinite bodies, derived from metamorphism of either mafic/ultramafic mantle or oceanic rocks, undergo dehydration with the plate subducted. With the buoyancy and combining plate convergence, the rock suite of the subduction channel, including serpentinite blocks and surrounding pelitic mélange, returns to the surface rapidly. Serpentinite bodies are relatively rigid and competent, and it is harder to deform and register fewer deformation features than the surrounding pelitic schist, which is much more incompetent. As a result, our field observations indicate that the surrounding materials can better reveal the dynamics of serpentinite in contact with it.
In Taiwan Yuli belt, along a ~10-km-long transect, the Chingshui creek exposed several 1-2-km wide massive serpentine bodies, surrounded by the pelitic schist in this region. A ~1-km-long section composed of two separate serpentinite bodies can be distinguished into four domains with different foliation trends around the contact zone with the serpentinite bodies. In domain I, the main fabric (S2 cleavage) shows an east-west trend, and shallow dip in the pelitic schist. The metasomatism is observed in the contact zone (i.e., the rim of serpentinite), manifested by highly stretching and folded talc-chlorite schist. In domain II, close to the serpentinite bodies, the main fabric (S2) in the pelitic schist shows an east-west trend with near-vertical dip. In domain III, away from the serpentinite, the trend of S2 in pelitic schist returns to the same trend with domain I, and domain IV, which is also the same trend of domain II. By reconstructing the geological structural cross-section across this 1-km-long section, we interpret that the serpentinite blocks within the pelitic mélange in the subduction channel acted, from deformation point of view, as porphyroblasts, where the main fabrics in the surrounding pelitic schist go around the edge of the porphyroblast of serpentine, in the high shear zone.
During the continental subduction within the subduction channel, serpentinite bodies, derived from metamorphism of either mafic/ultramafic mantle or oceanic rocks, undergo dehydration with the plate subducted. With the buoyancy and combining plate convergence, the rock suite of the subduction channel, including serpentinite blocks and surrounding pelitic mélange, returns to the surface rapidly. Serpentinite bodies are relatively rigid and competent, and it is harder to deform and register fewer deformation features than the surrounding pelitic schist, which is much more incompetent. As a result, our field observations indicate that the surrounding materials can better reveal the dynamics of serpentinite in contact with it.
In Taiwan Yuli belt, along a ~10-km-long transect, the Chingshui creek exposed several 1-2-km wide massive serpentine bodies, surrounded by the pelitic schist in this region. A ~1-km-long section composed of two separate serpentinite bodies can be distinguished into four domains with different foliation trends around the contact zone with the serpentinite bodies. In domain I, the main fabric (S2 cleavage) shows an east-west trend, and shallow dip in the pelitic schist. The metasomatism is observed in the contact zone (i.e., the rim of serpentinite), manifested by highly stretching and folded talc-chlorite schist. In domain II, close to the serpentinite bodies, the main fabric (S2) in the pelitic schist shows an east-west trend with near-vertical dip. In domain III, away from the serpentinite, the trend of S2 in pelitic schist returns to the same trend with domain I, and domain IV, which is also the same trend of domain II. By reconstructing the geological structural cross-section across this 1-km-long section, we interpret that the serpentinite blocks within the pelitic mélange in the subduction channel acted, from deformation point of view, as porphyroblasts, where the main fabrics in the surrounding pelitic schist go around the edge of the porphyroblast of serpentine, in the high shear zone.