Late Paleozoic to Mesozoic tectonic evolution of the Qinling Orogenic Belt: Structural and geochronological constraints from the Devonian Liuling Group, eastern Qinling area, China

Abstract

The Late Paleozoic to Mesozoic tectonic evolution of the Qinling Orogenic Belt is not fully understood. To address this, structural analysis and rutile U-Pb dating were performed on the Middle–Late Devonian Liuling Group located along the northern margin of the South Qinling Belt (SQB). Detailed structural analysis reveals that the Liuling Group experienced four main deformation events (D₁–D₄). Initial D₁ deformation is characterized by intrafolial folds (F₁) and a regional penetrative foliation (S₁). Subsequent D₂ is marked by SW-vergent asymmetric, overturned folds and related crenulation lineation (L₂). D₃ and D₄ are represented by, respectively, nearly E-W trending open folds and NNE-SSW trending centimeter-scale kink folds, both of which slightly modify D₁ and D₂ structures. Taking into account published chronological data, we propose that D₁ and D₂ occurred at 363–349 Ma and 332–318 Ma, respectively, and were associated with NE-SW oriented shortening during continental subduction of the SQB. Our new rutile U-Pb ages of 243–240 Ma provide a lower age limit for D₃ deformation, which was related to N-S oriented shortening triggered by continental collision between the South China Block (SCB) and SQB along the Mianlue Suture Zone (MLSZ). Finally, D₄ deformation was associated with the far-field effects of Late Jurassic subduction of the Paleo-Pacific Plate, which generated a WNW-ESE oriented shortening. Our findings suggest that continental subduction of the SQB continued until the earliest Late Carboniferous. Subsequently, the northern margin of the SQB experienced a Triassic metamorphic overprint triggered by collision between the SCB and SQB.