Tectonic Evolution of the Tethysides

By

A. M. Celal Sengr

Istanbul Technical University, Faculty of Mines, Istanbul, Turkey

The Tethysides are the super-orogenic complex that fringes Eurasia to the south and embodies the Alpine-Himalayan system of mountain ranges. Their present uniform morphology masks a complex history involving the elimination of two major oceans associated marginal basins. The older of these oceans, the paleo-Tethys, came into existence when Pangea was assembled during the Carboniferous. Subduction along both its northern and southern margins had already commenced when it formed. Subduction beneath the northern margin of Gondwana led to commencement of rifting of a strip of continent, called the Cimmerian Continent, during the Permian. Formation of the Westralian basin may also be associated with an earlier phase of this extension; the Gondwana rifts in India definitely are. This strip of continent began rotating northward toward Laurasia around a pole somewhere in southeastern Europe. In the process of rotation it fell apart and a number of ocean branches formed. The largest of these was the Banggong Co-Nu Jiang ocean, which extended from eastern Iran into southeast Asia. The first pieces of the Cimmerian Continent collided with Laurasia in the earliest Jurassic along a line extending from northern Turkey, through northern Iran, along the Paropamisus and the northern Pamirs, and the Kuen-Lun into eastern China. The Banggong Co-Nu Jiang closed in the Early Cretaceous. All these closures together formed the Cimmeride orogenic system. Northward subduction commenced south of the Cimmerian Continent pieces mainly in the Early Cretaceous, but intra-oceanic subduction in the ocean had started locally as early as in the Early Jurassic. That ocean is known as neo-Tethys. It closed following the disruption and dispersal of Gondwana: during the Cretaceous to Oligocene interval, parts of Apulia collided with Europe. Arabia seems to have commenced its collision with the easternmost digitations of Apulia in the Bitlis Massif by the early Eocene, but delayed its final collision with Eurasia in Iran and in eastern Turkey until the early-middle Miocene. India commenced contact with Eurasia in the latest Cretaceous and its final apposition along the Himalaya was completed by the late Eocene. The orogenic belt that resulted from the closure of neo-Tethys is called the Alpides. Alpides and Cimmerides together constitute the super-orogenic complex Tethysides. In contrast to the Altaids, little juvenile crust was generated along the Tethysides. They merely robbed Gondwana of crustal material, which they subsequently added to Laurasia. Compared with the Altaids, they have less subduction-accretion material in their architecture and, consequently, most of their sutures are of appositional type. Although the narrow suture belts of the Tethysides are characterized by steep fabric, the overall structure of the mountain belt is dominated by flat to moderately dipping nappes and associated structures. The Tethysides extensively deformed their fore- and hinterlands by semi-penetrative, blocky structures commonly rejuvenating Altaid structures in central and western Asia. Many such structures are basins rich in hydrocarbons.

AAPG Search and Discovery Article #90015©2002-2003 AAPG Distinguished Lectures