Thermo-kinematic evolution of the Taiwan oblique-collision mountain belt as revealed by zircon fission track dating

Based on analyses of about 970 zircon grain fission-track (FT) ages from 44 elastic rock samples collected from six transects and two pooled ages of a patite concentrates separated from a diabase body, the thermo-kinematic evo lution of the Taiwan mountain belt since the last orogenic phase (the Pengl ai Orogeny) has been delineated for the first time. As a consequence of the active Pengiai Orogeny since late Tertiary times, pre-orogenic FTs in detr ital zircons and apatites have been subjected to varying degrees of anneali ng by geothermal heating. The spatial boundary between the partial and comp lete resetting of zircons coincides well with that corresponding to the 260 degreesC isotherm between the greenschist facies and prehnite-pumpellite f acies defined previously by crystallinity of potassic micas. The age distri bution along each cross-section exhibits younger ages from the mountain fro nt toward the rear plate boundary between the Eurasian and the Philippine S ea plates, suggesting asymmetric cooling and exhumation. Along the strike d irection (roughly north to south) of the regional structure, the age distri bution reflects southward propagation of the arc-continent collision and su bsequent uplift-and-denudation. Spatially, the width of the zircon complete -reset zone gradually narrows down along the strike of the regional structu re, reflecting the southward propagation of the arc-continent collision and subsequent uplift-and-denudation. Temporally, zircon FT ages for the weste rn margin of the completely reset zone are progressively younger from 5-6 M a in the northern part to ca. 2 Ma in the south-central part, then resume t o ca. 6 Ma for the southern end, where collision is only in its initial sta ge. The previously tectonized pre-Tertiary Peikang Basement High on the Asi an continental margin plays an important role in defining the uplift-and-co oling history and shaping the major salient-and-recess structure and neotec tonics of the mountain belt. (C) 2001 Elsevier Science B.V. All rights rese rved.