Cretaceous and Cenozoic cooling history across the ultrahigh pressure Tongbai-Dabie belt, central China, from apatite fission-track thermochronology

The crystalline terrane of the Tongbai-Dabic region, central China, comprising the Earth's largest ultrahigh-pressure (UUP) exposure was formed during Triassic collision between the Sino-Korean and Yangtze cratons. New apatite fission-track (AFT) data presented here from the UHP terrane, extends over a significantly greater area than reported in previous studies, and includes the (eastern) Dabie, the Hong'an (northwestern Dabie) and Tongbai regions. The new data yield ages ranging from 44 +/- 3 to 142 +/- 36 Ma and mean track lengths between similar to 10 and 14.4 mu m. Thermal history models based on the AFT data taken together with published Ar-40/Ar-31, K-Ar, apatite and zircon (U-Th)/He and U-Pb data, exhibit a three-stage cooling pattern that is similar across the study region, commencing with an Early Cretaceous rapid cooling event, followed by a period of relative thermal stability during which rocks remained at temperatures within the AFT partial annealing zone (similar to 60-110 degrees C) and ending with a possible renewed phase of accelerated cooling during Pliocene to Recent time. The first cooling phase followed large-scale transtensional deformation between similar to 140 and 110 Ma and is related to Early Cretaceous eastward tectonic escape and Pacific back arc extension. Between this phase and the subsequent slow cooling phase, a transition period from similar to 120 to 80 Ma (to similar to 70 to 45 Ma along the Tan-Lu fault) was characterised by a relatively low cooling rate (similar to 3-5 degrees C/Ma). This transition is likely related to a tectonic response associated with the mid-Cretaceous subduction of the Izanagi-Pacific plate as well as lithospheric extension and thinning in eastern Asia. The present regional AFT age pattern is therefore basically controlled by the Early Cretaceous rapid cooling event, but finally shaped through active Cenozoic faulting. Following the transition phase the subsequent slow cooling phase pattern implies a net reduction in horizontal compressional stress corresponding to increased extension rates along the continental margin due to the decrease in plate convergence. Modelling of the AFT data suggests a possible Pliocene-Recent cooling episode, which may be supported by increased rates of sedimentation observed in adjacent basins. This cooling phase may be interpreted as a response to the far-field effects of the frontal India-Eurasia collision to the west. Approximate estimates suggest that the total amount of post similar to 120 Ma denudation across the UHP orogen ranged from similar to 2.4 to 13.2 kin for different tectonic blocks and ranged from similar to 0.8 to 9.7 kin during the Cretaceous to between similar to 1.7 and 3.8 kin during the Cenozoic. (c) 2006 Elsevier B.V. All rights reserved.