Cimmeria (continent)

Cimmeria was an ancient continent, or, rather, a string of microcontinents or terranes, that rifted from Gondwana in the Southern Hemisphere and was accreted to Eurasia in the Northern Hemisphere. It consisted of parts of present-day Turkey, Iran, Afghanistan, Pakistan, Tibet, China, Myanmar, Thailand, and Malaysia. Cimmeria rifted from the Gondwanan shores of the Paleo-Tethys Ocean during the Early Permian and as the Neo-Tethys Ocean opened behind it, during the Permian, the Paleo-Tethys closed in front of it. Because the different chunks of Cimmeria drifted northward at different rates, a Meso-Tethys Ocean formed between the different fragments during the Cisuralian. Cimmeria rifted off Gondwana from east to west, from Australia to the eastern Mediterranean.
It stretched across several latitudes and spanned a wide range of climatic zones.

History of the concept

First concepts

A "large, ancient Mediterranean Sea" was first proposed by Austrian palaeontologist Melchior Neumayr in 1883. Studying the distribution of Jurassic faunas, he concluded that an equatorial ocean stretching from India to Central America must have separated a large continent in the northern hemisphere from one in the southern hemisphere. Austrian geologist Eduard Suess named this Mesozoic ocean the Tethys, a mythical ocean which separated a mythical continent – Gondwanaland, home of the tongue-shaped flora – from a boreal continent. German geophysicist Alfred Wegener, in contrast, developed a concept of a single, global continent – the supercontinent Pangea – which, in his view, left no room for an equatorial ocean. A wedge-shaped, east-facing Tethys within Pangea was, nevertheless, proposed by Australian geologist Samuel Warren Carey in 1958. This ocean was later identified as a succession of oceans separated by north-migrating terranes or continental blocks, one of which was Cimmeria.

Iranian microcontinent

In 1974, after extensive field work in the Middle East, Swiss geologist Jovan Stöcklin identified the northern foot of the Alborz Range in northern Iran as the suture which in the Paleozoic was the northern shore of Gondwana and the remains of the Paleo-Tethys Ocean. Stöcklin also noted that an early Mesozoic or late Paleozoic rift separated the Iranian plate from the Arabian plate, and that another southern suture must be the remains of the Neo-Tethys Ocean. The opening of this later ocean, Stöcklin realized, must have transformed Iran into a microcontinent. Those observations made Stöcklin the first to identify a small part of what would later be known as Cimmeria.
Stöcklin also noted that his proposal resembled the old concept of the world in which there were two continents, Angaraland in the north and Gondwana in the south, separated by an elongated ocean, the Tethys. Iran belonged to neither continent but was part of the realm of Tethys.
Stöcklin's southern suture was later confirmed by observations of the evolution of microflora in Iran, which had a Gondwanan affinity during the Carboniferous but a Eurasian affinity during the Late Triassic – Iran had clearly drifted from Gondwana to Laurasia.

Eurasian superterrane

In the 1980s Turkish geologist Celâl Şengör finally extended Stöcklin's Iranian microcontinent further west to Turkey and further east to Tibet and the Far East. Şengör also reused the name introduced by Suess in 1901, the "Kimmerisches Gebirge" – the "Crimean" or "Cimmerian Mountains".
In the mountain range that now stretches from the Alps to Indonesia Şengör identified, using a simplified scheme, two distinct but superimposed orogenic systems containing a large number of anastomosing sutures: the older Cimmerides and the younger Alpides together forming what Şengör called the Tethysides super-orogenic system. These two orogenic systems are thus associated with two major periods of ocean closure: the earlier, northern, and much larger Cimmerides, and the later, southern, and smaller Alpides. Cimmeria was the long continental "archipelago" that separated the two oceans before the Paleo-Tethys closed.
This realm of Tethys thus covers most of Eurasia and a large time span :

Laurasia, Permian to Cretaceous
Palaeo-Tethys, Early Carboniferous to Middle Jurassic
Cimmeria, Triassic to Middle Jurassic
Neo-Tethys, Permian or Triassic to Eocene, locally still extant
Gondwana, Ordovician to Jurassic

This simple scheme, however, partly obscures the complex nature of the Tethyan cycles and terms such as "Eocimmerian" and "Neocimmerian" is often used for Late Triassic and Late Jurassic events respectively. Furthermore, a distinction is often made between two more recent Tethyan domains: the Alpine Tethys and the Neo-Tethys. The Alpine Tethys, the western domain in this scheme, separated south-western Europe from north-western Africa and was connected to the Central Atlantic. It is now completely closed and its suture encompasses the Maghrebids as well as the Apennines and the Alps. The Neo-Tethys, the eastern domain, opened between Arabia and the Cimmerian terranes. The East Mediterranean basin and the Gulf of Oman are considered relics of the Neo-Tethys which is thus still closing. These two domains were connected east of Sicily until the end of the Jurassic.

Tectonic history

In the Late Paleozoic, when the Cimmerian blocks were still located on the northern margin of Gondwana, they were far away from any active margins and orogenic belts, but they had been affected by thermal subsidence since the Siluran opening of Paleo-Tethys. Carboniferous to Permian ophiolites along suture zones in Tibet and north-eastern Iran indicate that the active margin of Paleo-Tethys was located here.
It was slab-pull forces in the Paleo-Tethys that detached Cimmeria from Gondwana and opened the Neo-Tethys. The mid-ocean ridge in the Paleo-Tethys subducted under Eurasia, as evidenced by Permian MORB in Iran. Slab roll-back in the Paleo-Tethys opened a series of back-arc basins along the Eurasian margin and resulted in the collapse of the Variscan cordillera. As the Paleo-Tethys subducted under the Eurasian southern margin, back-arc oceans formed from Austria to China. Some of these back-arcs closed during the Cimmerian orogeny, others remained open leading to the formation of younger back-arc oceans.

Turkey

Turkey is an assemblage of continental blocks that during the Permian were part of the northern margin of Gondwana. During the Permian-Triassic, as the Paleo-Tethys subducted under this margin a marginal sea opened and quickly filled with sediments. During the Late Triassic the Neo-Tethys began opening behind Cimmeria when the Eastern Mediterranean and its two eastern branches opened into the Bitlis–Zagros ocean.
During Early Jurassic, Cimmeria began to disintegrate behind the Paleo-Tethyan volcanic arc. This opened the northern branch in the Neo-Tethys—the Intra-Pontide, Izmh–Ankara, and the Inner Tauride oceans. The closure of the Paleo-Tethys in the Middle Jurassic reduced the Cimmerian archipelago in Anatolia. South of the Cimmerian blocks there were now two branches of the Neo-Tethys, a northern, larger and more complex, and a southern, more reduced. The Anatolide–Tauride continent separated them; the small Sakarya continent was located within the northern branch. The Apulian continent was connected to the Anatolide–Tauride continent.
These Neo-Tethyan branches reached their maximum width during the Early Cretaceous, after which subduction under Eurasia gradually consumed them. During the Middle-Late Cretaceous this subduction opened a back-arc basin, the Western Black Sea Basin, which stretched west into the Balkans north of the Rhodope-Pontide island arc there. In the Cretaceous, this basin pushed the Istanbul terrane southward in front of it, from the Odesa Shelf in the north-western Black Sea. In the Eocene, the terrane finally collided with Cimmeria thereby ending the extension in the western Black Sea. Contemporaneously, the East Black Sea Basin opened when the East Black Sea Block was rotated counter-clockwise towards Caucasus.
In the late Cretaceous northwards intra-oceanic subduction within the Neotethys gave way to the obduction of ophiolitic nappes over the Arabian platform from Turkey to Oman region. North of this subduction zone, remnants of the Neotethys ocean started to subduct northwards and led to the collision of Tauride Block with the Arabian plate during post-Oligocene times. North of these systems, the Tauride block collided with the southern margin of Eurasia by the end of the Cretaceous. Convergence continued until the end of Oligocene. The Arabian-Eurasian collision in eastern Turkey during the Late Eocene closed the two basins.
During the Paleogene Neo-Tethyan oceanic crust attached to the African plate subducted along the Crete and Cyprus trenches. The Anatolide-Tauride continent collided with the Pontide and Kırşehir blocks in the Late Paleocene-Early Eocene. This closed the Ankara-Erzincan branches of the northern Neo-Tethys. During this closure, slab roll-back and break-off in the Eocene resulted in inversion in the Pontides and widespread magmatism in northern Turkey. Extension and upwelling followed, resulting in melting of lithospheric material beneath the Pontides.
In southern Turkey the northward subduction of the Neo-tethys along the Bitlis–Zagros subduction zone resulted in magmatism in the Maden-Helete arc during the Late Cretaceous-Eocene and back-arc magmatism in the Taurides. The Bitlis–Zagros subduction zone finally closed in the Miocene and throughout the Oligocene-Neogene and Quaternary volcanism became increasingly localised. In the Late Oligocene, slab roll-back in the Hellenic Trench resulted in extension in the Aegean and western Turkey.

Iran

The subduction of western Neo-Tethys under Eurasia resulted in extensive magmatism in what is now northern Iran. In the Early Jurassic this magmatism had produced a slab pull force which contributed to the break-up of Pangea and the initial opening of the Atlantic. During the Late Jurassic-Early Cretaceous the subduction of the Neo-Tethys mid-ocean ridge contributed to the break-up of Gondwana, including the detachment of the Argo-Burma terrane from Australia.
The Central-East Iranian Microcontinent sutured with Eurasia in the Late Triassic during the regional "Eocimmerian" orogenic event in northern Iran, but Iran is made of several continental blocks and the area must have seen a number of ocean closures in the Late Paleozoic and Early Mesozoic.