Collision and rotation of the South China block and their role in the formation and exhumation of ultrahigh pressure rocks in the Dabie Shan orogen

Abstract

Terra Nova, 24, 339–350, 2012AbstractStudies of regional plate‐scale processes that may influence the exhumation of ultra‐high pressure (UHP) metamorphic rocks are few despite their potential importance. Here, we review and summarize available age constraints along with the Qinling‐Dabie Shan orogen, which separates the North China Block (NCB) from the South China Block (SCB). We find that collision‐related events in the west and extension‐related events in the east, where the large Dabie Shan UHP terrane is located, were contemporaneous. Available palaeomagnetic data indicate clockwise rotation of the SCB relative to the NCB during this time. Previous work indicated that the collision propagated from east to west where indentation of the SCB into the Qinling‐Dabie Shan orogen was active in the Hannan Dome area at 165 ± 3 Ma as constrained by new 40Ar/39Ar dates on synkinematic sericite in an indentation‐related mylonitic shear zone. While this contraction was occurring in the west, exhumation of the UHP terrane was occurring in the Dabie Shan in the east. We propose that the collision of the SCB with the NCB occurred not only in a scissor‐like fashion, as previously suggested, but also involved a later rotation about a pole west of the Dabie Shan during the closure of the Mianlue Ocean. As a consequence of this rotation, extension occurred between the South China Block and North China Block east of the pole of rotation leading to extensional exhumation of the Dabie Shan orogen. This microcontinent‐scale rotation of the SCB may have provided an important component in the exhumation of the largest UHP terrane in the world.