Late Palaeozoic To Late Triassic Northward Accretion And Incorporation Of Seamounts Along The Northern South Pamir: Insights From The Anatomy Of The Pshart Accretionary Complex

Late Palaeozoic-Mesozoic volcano-sedimentary rocks within the Rushan-Pshart Suture zone in the Pamir contain critical information on the subduction-accretion history of the Rushan-Pshart Ocean (Meso-Tethys) prior to the Central-South Pamir collision. In this article, we report new field, petrographic, geochronological, and geochemical data of the Permian to Triassic basic volcanic and sedimentary rocks from the Pshart area. Our field study unravels block-in-matrix components within some sedimentary melanges, which, together with some previously defined ophiolitic melanges, enables us to define the Pshart accretionary complex (AC), and thus for the first time to discuss the subduction-accretion history of the Rushan-Pshart Ocean and the growth of the Pshart AC. The youngest detrital U-Pb zircons suggest that deposition of sediments was in the Late Triassic (212 Ma). Detritus of Triassic age was primarily derived from the Triassic Karakul-Mazar Arc-AC (Northern Pamir) and the Bashgumbaz Magmatic Arc, which developed along the northern margin of South Pamir. The evidence of north-directed thrusts along the Kara Djilga-2 and Ken Djilga transverses confirms previous interpretations of southward subduction of the Rushan-Pshart oceanic lithosphere beneath the South Pamir. Geochemical OIB-type data of the Pshart alkaline basaltic rocks suggest formation in seamounts incorporated into the Pshart AC during the southward subduction of the Rushan-Pshart Ocean. The youngest Late Triassic deposition age is consistent with the coeval time of closure of the Palaeo-Tethys and Meso-Tethys oceans in the Pamir. The Pshart AC formed by subduction-accretion processes during the southward subduction of the Meso-Tethys Ocean along the northern South Pamir and the final docking of the Central and South Pamir (Cimmerian Blocks) may have occurred after the Late Triassic.