From convergent plate margin to arc-continent collision: Formation of the Kenting Melange, Southern Taiwan

摘要

The KentingMelange on the Hengchun Peninsula, Taiwan, formed through tectonic shearing of subduction complex lithologies, probably within the plate boundary subduction channel between the Eurasian and Philippine Sea plates, with further deformation and exhumation in the Pliocene-Pleistocene during arc-continent collision. Field relations reveal a structural gradation from normal stratified turbidite sequence (Mutan Formation) through broken formation to highly sheared Kenting Melange containing allochthonous polygenic blocks. This gradation is consistentwith an increase of average vitrinite reflection values from -0.72% in theMutan Formation through similar to 0.93% in the broken formation to similar to 0.99% in theMelange, suggesting temperatures of at least 140 degrees C during formation of the Kenting Melange. Zircons fromgabbro in the KentingMelange are dated as 25.46+/-0.18Ma, which togetherwith geochemical data constrains the source to South China Sea oceanic lithosphere. In combination with the field relationships, vitrinite reflectance values, microfossil stratigraphy, and offshore geophysical data fromS and SE Taiwan, we propose that the KentingMelange initially formed at the subduction plate boundary from off-scraped trench deposits. Minor Plio-Pleistocene microfossils (<5%) occur within the Melange in proximity to slope basin of equivalent age and were likely sheared into the Melange during out-of-sequence thrusting associated with active arc-continent collision, which in the Hengchun Peninsula commenced after 6.5 Ma. (C) 2015 International Association for Gondwana Research. Published by Elsevier B. V. All rights reserved.