The Cimmeride Orogenic System and the Tectonics of Eurasia
The Alpine-Himalayan system of orogenic belts is the product of the obliteration of Tethys. The Tethyan domain consisted, during the early and middle Mesozoic, of two oceans separated by a strip or string of continent(s), called the Cimmerian Continent, which had begun separating from the northern and northeastern margin of Gondwana-Land mainly during Triassic time, although rifting in the eastern-most parts had begun earlier. North of this Cimmerian Continent lay Paleo-Tethys, the original, east-facing, equatorial embayment of Permo-Triassic Pangea. To the south Neo-Tethys was evolving at the expense of Paleo-Tethys. In the eastern Tethyan domain, three large, independent continental pieces, namely the North China and South China Platforms and the Indochina Block, all possibly of Gondwanian origin, took part in Tethyan evolution and effected the division of eastern Tethys into a number of branches.
The double closure resulting from the Late Triassic to the present elimination of the two Tethyan oceans generated a double, largely over-printed orogenic system. That which resulted from the closure of Paleo-Tethys is here called the Cimmerides, including a multi-strand suture network that extends from the eastern Carpathians to the Pacific shores—from the Sea of Okhotsk to eastern Sulawesi, and for that orogen, which is the product of the disappearance of Neo-Tethys, the designation Alpides is reserved. As far east as Afghanistan and in Indonesia, the Cimmeride orogen is almost completely overprinted by Alpide structures, but in Tibet and China the increasing width of the continental pieces separating Paleo-Tethys from Neo-Tethys effected a clear spatial distinction of the Cimmerides from the Alpides.
From the eastern Carpathians to the Caucasus, the Cimmeride orogen is asymmetric and simple, with north-facing orogenic polarity (i.e., predominant pre-collision subduction polarity). In this segment it was constructed largely atop earlier Hercynian structures, making the recognition and reconstruction of Cimmeride structures extremely difficult. Between the eastern Caucasus and the 92°E meridian, it is asymmetric, with south-facing orogenic polarity, and contains a complex Laurasia-bound orogenic collage consisting dominantly of ophiolitic mélange/flysch packages. East of 92°E it is generally symmetric, involving large, multiple, both Laurasia- and Cimmerian Continent-bound collages, and east of the Songpan-Ganzi system it becomes multi-branched. Along the entire orogen, terminal collisions took place between the late Middle Triassic and the Late Jurassic. From Afghanistan to Indonesia, the smaller orogen of the Waşer-Tanggula-Sittang Valley/Myitkyina zone, of Middle Jurassic-Early Cretaceous age, and the latest Triassic Karakaya Orogen in Turkey are located south of the main trunk of the Cimmerides. They grew out of intra-Cimmerian Continent mini-oceans that may have begun opening locally as Paleo-Tethyan marginal basins.
Extensive fore- and hinterland areas of complex thrust, strike-slip, and normal fault deformation accompany the entire strike-length of the orogen from eastern Europe to Indochina and include such well-known structures as the Late Triassic-Early Jurassic compressional belt of Donetz, the Turan block-fault terrain and a major part of the West Siberian Basin Complex, the east Iranian Flysch Zone, and the Angaran inversion structures. Most of the Cenozoic structures north of the Alpine-Himalayan belt seem to have nucleated on these older Cimmeride fore- and hinterland structures. The analysis presented here suggests that nearly all of the Eurasian “intra-cratonic” structures, classically viewed by some geologists to have resulted from primary vertical movements, may be products of horizontal movements caused by repeated orogenies around the periphery of cratons.
Understanding the evolution of the Cimtnerides together with their fore- and hinterlands sheds much light on the Mesozoic tectonics of all of Asia and eastern Europe and leads to a number of interesting concepts concerning continental evolution, such as “hidden subduction.” Finally, a study on the evolution of ideas on the Cimmerides clearly shows how much we remain under the spell of the Kober-Stillean fixist philosophy.