Middle Jurassic collision of an exotic microcontinental fragment: implications for magmatism across the southeast China continental margin

摘要

Thrusting, folding and metamorphism of late Paleozoic to middle Mesozoic sedimentary rocks, togetherudwith high precision U–Pb zircon ages from Middle to Late Jurassic volcanic and granitic rocks,udreveals evidence for a major deformation event in northwestern Hong Kong between 164 and 161 Ma.udThis episode can be linked with collision of an exotic microcontinental fragment along the southeastudChina continental margin determined from contrasting detrital zircon provenance histories of late Paleozoicudto middle Mesozoic sedimentary rocks either side of a NE-trending suture zone through centraludHong Kong. The suture zone is also reflected by isotopic heterogeneities and geophysical anomaliesudin the crustal basement. Detrital zircon provenance of Early to Middle Jurassic rocks from theudaccreted terrane have little in common with the pre-Middle Jurassic rocks from southeast China. Instead, the zircon age spectra of the accreted terrane show close affinities to sources along the northern margin of east Gondwana. These data provide indisputable evidence for Mesozoic terrane accretion along the southeast China continental margin. In addition, collision of the exotic terrane, accompanied by subduction roll-back, is considered to have hastened foundering of the postulated flat-slab beneath southeast China leading to a widespread igneous flare-up event at 160 Ma.