Tethys Evolution in the Afghanistan-Pamir-Pakistan Region

Abstract

The Afghanistan-Pamir-Pakistan ranges resulted from compression of the Tethyan realm. Continental basement rocks under cover of shallow-marine sediments indicate that the Tethys was largely an epicontinental sea. Early-Middle Paleozoic and Mesozoic oceanic environments are indicated by ophiolitic associations in a Paleotethyan suture in the north and a Neotethyan suture in the south, which divide the epicontinental realm into three major domains. The Northern Domain represents the south margin of Paleo-Asia affected by Hercynian and Indosinian orogenic processes. Several large blocks constitute the Central Domain, in which Early Cretaceous and Early-Middle Tertiary folding and magmatism played a dominant role. The Southern Domain occupies the Mesozoic shelf of the Indian subcontinent folded and imbricated in the Neogene. In the plate-tectonic concept the fundamental orogenic mechanism is continental collision resulting from successive detachment of the Central and Southern Domains from Gondwanaland and their north-drift across a wide Tethys Ocean; folding started with Late Triassic collision along the Paleotethyan suture, to be followed by Early Tertiary collision along the Neotethyan suture, with a possible intermediate collision event in the Early Cretaceous along a poorly documented additional suture bisecting the Central Domain. The model requires large-scale subduction of Tethyan oceanic crust to compensate spreading in the Neotethyan and Indian Oceans. Subduction is held responsible for the calc-alkaline magmatism of the region. The author^’s main objection against this model is the lack of geological evidence for the existence of the vast Late Paleozoic Tethys Ocean supposed to have been available for Mesozoic subduction. An excess of crustal expansion in the Indian Ocean over crustal shortening in the orogenic belt, tantamount to an expansion of the Earth, is concluded.