Clastic carbonates in the South Sistan Basin (SE Iran): implications for subduction vergence and timing of collision

The N-S-trending Sistan Suture Zone in East Iran results from the collision of the Lut and Afghan continental blocks. The southern Sistan Basin hosts Eocene terrigenous deep-marine turbiditic sequences with carbonate olistoliths, debris-flow sheets and calcareous turbidites. These carbonates represent one or several early to middle Eocene carbonate platforms fragmented and redeposited in a deep-marine environment. Palaeocurrent measurements on the terrigenous and calcareous turbidites show that the source carbonate platform was located on the Afghan active margin. Volcanic debris in the limestone and surrounding turbidites corroborate an active magmatic margin on the Afghan side. The formation of limestone debris-flow sheets is attributed to increased erosion and retreat of the carbonate platform, potentially triggered by the closure of the Sistan Basin and continental collisions in the late middle Eocene, after subduction of the Sistan Ocean beneath the Afghan Block.