Kinematics and structural evolution of the slate belt and metamorphic core of an active arc-continent collision, Taiwan

Taiwan is an active arc-continent collision situated along the boundary between the Eurasian and Philippine Sea plates and is a result of the collision between the Luzon island arc and the Asian continental margin. To characterize the kinematics of deformation in the Taiwan orogen, detailed structural mapping and kinematic analyses were conducted along two transects in the slate belt and metamorphic core of Taiwan (the Hsuehshan Range and pre-Tertiary metamorphic complex, respectively).; The Hsuehshan Range is a structural high exposed in the middle of the mountain belt and is characterized by a steep, SE-dipping cleavage and a downdip stretching lineation. Syntectonic fibrous overgrowths in pressure shadows record coaxial strain histories across most of the range and show a general increase in strain magnitude toward the hinterland. Near the eastern boundary of the Hsuehshan Range, however, pressure shadows have curved fibers indicating a top-to-the-SE (backthrust) sense of shear. Thus, the Hsuehshan Range is a pop-up structure bounded to the west by a series of NW-vergent imbricate thrusts and to the east by a SE-vergent backthrust. This backthrust is interpreted to have initially developed as a west-dipping normal fault during Paleocene through Oligocene rifting of the South China Sea. This normal fault was subsequently reactivated as a backthrust during the collision.; The pre-Tertiary metamorphic complex is characterized by dominant schistosity that dips moderately to the NW and a lineation that plunges shallowly to the NE approximately parallel to the margin. Kinematic indicators, including S-C fabrics, asymmetric inclusion trails, sheath folds, and duplex structures, record a consistent top-to-the-NE sense of shear and are interpreted to reflect left-lateral offset related to the obliquity of the collision. The change from a downdip lineation in the external part of the orogen to a horizontal lineation in the internal part suggests that oblique convergence is partitioned into a strike perpendicular component in the foreland and slate belt and a strike-parallel component in the hinterland.