Chemical analysis of scaly fabric: subduction zone deformation structures from the Shimanto Belt, Japan
Open Access
Author:
Taylor, Jennifer Margaret
Area of Honors:
Geosciences
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
Donald Fisher, Thesis Supervisor Dr. Maureen Feineman, Thesis Honors Advisor
Keywords:
scaly fabric Shimanto Belt subduction zone silica dissolution electron microprobe Japan
Abstract:
Scaly fabrics in rocks from accretionary prisms provide insight into mechanical processes occurring in subduction fault zones. Nonetheless, the extent to which chemical processes contribute to the formation of scaly fabrics, and how these processes may vary with depth, has been poorly studied to date. Mélange shales from two different paleo-depths in the ancient subduction fault zones of the Shimanto Belt, Japan, were analyzed by electron microprobe to determine chemical differences between the host rock and shear zones. Structural and mineralogical differences were observed between samples from different paleo-depths. Shear zones in all samples were found to be depleted in silica, while quartz veins may provide a mass balance to silica loss. Silica dissolution and precipitation may contribute to the development of shear zones and scaly fabrics in subducted sediments from the accretionary prism. This process is a potential mechanism for frictional healing of the subduction fault zone, with implications for earthquake mechanics.