Thermal structure of the Dabie eclogite-bearing terrane revealed from the results of Ti-in-zircon thermometry

Investigation of thermal structure is critical to the interpretation of regional geological structure. This study sampled 12 gneissic outcrops along an approximately 35 km-long profile striking north–south in the Dabie eclogite-bearing terrane. Nanoscale secondary-ion mass spectrometry (Nano-SIMS) was used to analyse the Ti content of zircons from the rocks, and a Ti-in-zircon thermometer was adopted to measure the metamorphic temperatures of formation. Zircons contain three or four different cathodoluminescent (CL) zones, which correspondingly yield significant metamorphic temperature estimates. The metamorphic temperatures decrease along the formation sequence of zircon zones, suggesting that zircon zones formed along an exhumation pressure–temperature ( P – T ) path. The peak metamorphic temperatures recorded in zircons from gneissic samples range from 500 to 800°C and appear to be comparable with the results from the eclogites enclosed in corresponding gneisses. The determined peak metamorphic temperatures yield large temperature differences from 50 to 200°C between neighbouring petrological units or samples, which occur within distances of 1–4 km. The distinct temperature differences suggest that the Dabie eclogite-bearing terrane consists of a stack of seven or eight tectonometamorphic slices along the profile.