Did along-strike changes in continental subduction styles occur in the Dabie-Sulu orogenic belt?

Abstract

The Triassic collision between the North China Block (NCB) and the South China Block (SCB) formed the Dabie-Sulu orogenic belt, renowned for its extensive ultra-high-pressure metamorphic rocks and the prominent Tan-Lu Fault. Geological and geophysical data reveal significant along-strike differences in both shallow and deep structures within the belt, raising a critical question: What tectonic processes drive these structural variations? Considering that the Triassic collision involved pre-collisional accreted microcontinents and along-strike variations in convergence velocities, this study investigates the influence of microcontinental width, convergence rate, and initial Moho temperature on continental subduction styles using numerical modeling. The models incorporate pre-collisional accreted microcontinent(s) and reveal a two-stage subduction evolution: an initial transition from one-sided to two-sided continental subduction, followed by subduction polarity reversal. High initial Moho temperatures, rapid convergence rates, and wide accreted microcontinents promote the development of two-sided subduction, characterized by an initially vertical interface that gradually inclines towards the pro-plate as convergence progresses. These subduction styles significantly influence crustal suture migration. One-sided subduction results in minimal horizontal displacement, whereas two-sided subduction and polarity reversal lead to substantial horizontal shifts. Based on the modeling results, this study proposes a new evolutionary model for the Dabie-Sulu orogenic belt during the NCB-SCB collision. The model effectively explains along-strike structural differences, such as the inconsistent tectonic trends on either side of the Tan-Lu Fault and the opposite dipping directions of high-velocity mantle anomalies observed in geophysical profiles. Furthermore, the proposed model sheds light on the formation and evolution of the Tan-Lu Fault.