Material Composition of the Newly Discovered Zongzhuo Formation Sedimentary Mélange in the Dingri Area, Southern Tibet, and its Constraints on the Basin Controlling Dingri–Gamba Fault

Abstract

The study of sedimentary mélanges holds pivotal importance in understanding orogenic processes and unveiling geodynamic mechanisms. In this study, we present findings on zircon U-Pb isotopes and whole-rock elemental data concerning the recently uncovered Zongzhuo Formation sedimentary mélanges within the Dingri area. Field observations reveal the predominant composition of the Zongzhuo Formation, characterized by a matrix of sandstone-mudstone mixed with sand-conglomerates within native blocks exhibiting soft sediment deformation. Moreover, exotic blocks originating from littoral–neritic seas display evidence of landslide deformation. Our study identifies the depositional environment of the Zongzhuo Formation in Dingri as a slope turbidite fan, with its provenance traced back to the passive continental margin. Notably, this contrasts with the Zongzhuo Formation found in the Jiangzi–Langkazi area. Based on existing data, we conclude that the Zongzhuo Formation in the Dingri area was influenced by the Dingri–Gamba fault and emerged within a fault basin of the passive continental margin due to Neo-Tethys oceanic subduction during the Late Cretaceous period. Its provenance can be attributed to the littoral–neritic sea of the northern Tethys Himalaya region. This study holds significant implications for understanding the tectonic evolution of Tethys Himalaya and for reevaluating the activity of the Dingri–Gamba fault, as it controls the active deposition of the Zongzhuo Formation.