The Contribution of NE-SW Stretching To Exhumation of the Metamorphic Core of the Southern Central Range of Taiwan: Constraints from a Peak Temperature Proxy

To date most efforts to understand ongoing and recent rock exhumation in Taiwan's Central Range have focused on transects-of-opportunity afforded by highways that cross the mountains. Nearly all efforts to understand geodetic data and peak temperature proxies have treated these transects as appropriate for making profiles and attempting structural reconstructions. Our analyses of mesoscale fault kinematic data and earthquake focal mechanisms in the area of the South Cross Island Highway (SXIH) show that active and recent brittle strain is accommodating NE-SW maximum principal stretching. Thus, highway-parallel (orogen-normal) profiles reflect non-plane strain. A recently published age-elevation transect along the SXIH suggests 5 mm/yr exhumation rates during the last 2 Myr. If the NE-SW stretching that we have documented has been operating over a similar timeframe we hypothesize that the faults and shear zones accommodating this stretching may be contributing to the exhumation of the metamorphic core. The distribution of mesoscale faults and earthquake hypocenters suggest that the manifestation of NE-SW stretching varies from west to east. In particular normal faulting (i.e., crustal thinning) is dominant in the west near Litao whereas strike slip faulting is dominant in the east near Haiduan. Preliminary analyses of carbonaceous schist collected from NE-SW transects show a northeastward increase in peak temperature based on Raman Spectroscopy on Carbonaceous Material (RSCM). We suggest that the thermal structure as recorded by peak temperatures will show discontinuities that reflect a km-scale zone of crustal thinning.