Is the HP–UHP Hong’an–Dabie–Sulu orogen a piercing point for offset on the Tan–Lu fault?

Abstract

The Tan–Lu fault is a major strike-slip fault in eastern China that appears to offset the high-grade rocks of the Hong’an–Dabie–Sulu orogen left-laterally ∼540km. We evaluate models for the collision between the South and North China blocks, published radiometric dates recording HP–UHP metamorphism and exhumation in the Hong’an–Dabie and Sulu terranes, and the timing of sinistral motion on the Tan–Lu fault to evaluate whether UHP rocks provide a piercing point for offset on the Tan–Lu fault. UHP metamorphism in Hong’an–Dabie was concurrent with Sulu based on U–Pb dating of coesite-bearing domains of zircon at 244±5–226±2Ma for Hong’an–Dabie and 243±4–225±2Ma for Sulu. Retrograde metamorphism began c. 220Ma for both Hong’an–Dabie and Sulu, but retrograde zircon growth ended c. 214Ma in Hong’an–Dabie and continued until c. 202Ma in Sulu based on U–Pb dating of zircon domains external to coesite-bearing domains. Structures in Sulu are rotated 25° counter-clockwise from, but are broadly similar to, Hong’an–Dabie suggesting the two areas have a common Triassic orogenic history that pre-dates motion on the Tan–Lu fault, and that is consistent with paleomagnetic studies. We constructed a pre-Cretaceous restoration of the Hong’an–Dabie–Sulu belt that moves the Sulu terrane south, aligning the suture and the eclogite-facies isograd, and rotates Sulu c. 25° clockwise to re-align structures with Hong’an–Dabie. Our restoration is supported by published data and shows that the Hong’an–Dabie–Sulu orogen is a piercing point for post-collisional offset on the Tan–Lu fault and that these regions shared a common subduction–exhumation history. The Tan–Lu fault did not play a significant role in the Hong’an–Dabie–Sulu collision and likely developed later, in the Early Cretaceous.