CHANGING STRETCHING DIRECTIONS IN THE EASTERN CENTRAL RANGE OF TAIWAN: A RECORD OF SUBDUCTION AND EXHUMATION KINEMATICS FROM A SEAFLOOR SECTION

Taiwan records active arc-continent collision between the northwestern edge of the oceanic Philippine Sea Plate (PSP) and the Chinese Passive Margin. Oblique movement of the PSP to the northwest at about 82 mm/yr and the local subduction of the Eurasian Plate off the coast of China results in extremely high exhumation rates. Widely cited plane strain models of the collision argue for material flux from the western pro-wedge and the South China Sea (SCS) to the eastern retro-wedge. Recent alternative 3-dimensional models of the collision suggest material flux approximately normal the plate motion vector, with flow toward either the north northeast or south southwest. Resolving the exhumation pathways requires constraints on kinematics which are elusive in the poly-deformed schists and marbles that dominate the eastern Central Range. Here we exploit a well-preserved sequence of greenstone with shale drapes (now phyllite) and quartz dominated pebbly phyllite from the Mugua River in the Tailuko Belt that we suggest is a marine stratigraphic section. This sequence appears to record greenschist facies metamorphism and retrograde metamorphism during advection from the SCS. Bulk-rock chemistry of the greenstone sample was obtained using X-ray fluorescence and inductively coupled plasma mass spectrometry methods, resulting in the classification of a mid-ocean ridge basalt based on FeO, MgO, and Al₂O₃ concentrations. Plagioclase clasts in the phyllite where it is intercalated with the greenstone appear to be well preserved, whereas those within the more massive greenstone are substantially recrystallized. Strain fringes around the plagioclase suggest either a single episode of 3-dimensional strain or a record of two distinct stretching directions. We will share energy dispersive spectroscopy and wavelength dispersive spectroscopy data collected via the scanning electron microscope and electron probe microanalysis for strain fringes in hopes of resolving between these two end-member histories.