Analysis of Structural and Magnetic Fabric in the Backbone Range of Taiwan and Its Tectonic Implications

Exhumation process of HP-UHP rock is always a fascinating puzzle for solid earth sciences. Analyses of structures and strain distribution associated with rapid exhumation of the late Cenozoic blueschist-facies rock along the Yuli belt of the eastern Backbone Range in Taiwan is essential to shed light on understanding the structural history and kinematic evolution of orogenic belts.

Normal shear parasitic folds, associated sub-horizontal axial plane crenulation cleavages (S3), subvertical quartz veins and subvertical joints subparallel to the motion of the Philippine Sea Plate quite often observed in the eastern Backbone Range are late stage structures overprinted on regionally fan-like foliation (S2) across the Backbone Range. Subhorizontal stretching lineation with both sinistral and dextral shear is dominated in the eastern Backbone Range. On the other hand, downdip stretching lineation with the top-to-west shear is profound in the western Backbone Range. 1D shortening analyses of S3-related folds can provide the deformation constraint related to S3 cleavage. Furthermore, magnetic fabric examination of anisotropy of magnetic susceptibility (AMS) will afford the strain ellipsoid pattern regionally among Taroko, Yuli and slate belts. These structure observations and strain distribution pattern must be taken into consideration for hypothesizing the exhumation processes of Taiwan mountain belt.