ABSTRACT Orogenic belts, the main factories of continental crust and the most efficient agents of continental deformation, are commonly extremely complex structures. Every orogenic belt is unique in detail, but they are generally similar to each other, having mainly been products of subduction and continental collision. Because of that common origin, they all share common functional organs, such as magmatic arcs, various back-arc and retro-arc features, and multifarious fore-arc environments, collisional sutures, etc. The modern orogenic belts usually display adequate detail about these organs, enabling us to identify them even when they are deformed or otherwise dislocated. In reconstructing now-disrupted orogenic belts, we are after one or more Ariadne’s threads to follow the original structure from one package of rock to another. The most prominent, laterally persistent, and easy-to-follow structures among the major orogenic features are the magmatic arcs. As they are the common expression of their subduction zones, they form linear or arcuate lines along the strike, and they usually move episodically inwards or outwards, being located behind sharply defined magmatic fronts. Present-day dating techniques provide high-resolution dates from magmatic rocks, and the migration of the magmatic front is easily detectable. They form the main Ariadne’s thread in orogenic studies. Where they are absent, the most helpful structures possessing lateral persistence are the now-deformed Atlantic-type continental margins and suture zones. We chose two major fossil orogenic belts, namely, the Tethysides, and the Altaids, to emphasize the methodology of comparative anatomy of orogenic belts. There have been many theories regarding the evolution of these orogenic belts. However, they are either local, only dealing with a small portion of orogen, or they are in conflict with presently active processes. We underline the importance of magmatic fronts as reliable witnesses of the geodynamic evolution of major orogenic collages. This paper aims to disperse the mist upon the reconstructions of complexly deformed orogenic belts with the simplest possible interpretations that help us to form testable hypotheses that can be checked with a variety of geological databases.

ABSTRACT The Intra-Pontide suture is the boundary between the İstanbul Zone and the Sakarya Continent in northwest Turkey. Our new paleontological and stratigraphic data show that the subduction of the Intra-Pontide Ocean was still going on between the late Cretaceous and the early Tertiary. This is in contrast to the recently reported Santonian closure of the Intra-Pontide Ocean. We have gathered much of the earlier published stratigraphic, paleontological, and radiogenic data on both the metamorphic units and the unmetamorphosed sedimentary basins along and near the Intra-Pontide suture. Our analysis shows two successive accretionary prisms were formed along the western and the central segments of the suture zone: (1) an Upper Cretaceous blueschist-eclogite facies metamorphic prism in the Biga Peninsula, and (2) an Upper Jurassic–Lower Cretaceous greenschist-epidote amphibolite facies metamorphic prism between the Armutlu Peninsula and Almacik Mountains. However, in the eastern third segment, Middle Jurassic and Middle to Upper Cretaceous high-pressure–low temperature (HP-LT) and low-pressure–low temperature (LP-LT) subduction-accretion complexes cover a large area, creating the Central Pontide Supercomplex. Between the late Cretaceous and late Paleocene, when the Rhodope-Pontide arc was evolving, an Upper Cretaceous–Paleocene forearc basin (the Kocaeli Basin) consisting of Upper Santonian–Campanian volcanogenics and overlying Upper Campanian–Selandian pelagic limestones also formed over the İstanbul Zone, which formed the hinterland. The paleontological data suggest that collision between the İstanbul Zone and the Sakarya Continent must have occurred later than the early Ypresian. An Upper Cuisian molasse covers all the older units, suggesting a possible medial Cuisian closure (ca. 51 Ma). This closure age can also be correlated with the similar, previously published fission-track uplift ages along the Intra-Pontide suture. Following the medial Cuisian closure of the Intra-Pontide Ocean, a wedge-shaped transtensional intramontane basin, the Thrace molasse basin, opened while the westerly escaping fragments of the Intra-Pontide suture tore off a piece of the Strandja system during the medial Eocene–Oligocene interval.

The Tethyan realm stretches across the Old World from the Atlantic to the Pacific Oceans along the Alpine-Himalayan mountain ranges and extends into their fore- and hinterlands as far as the old continental margins of the now-vanished Tethyan oceans reached. It contains the Tethyside superorogenic complex, including the orogenic complexes of the Cimmerides and the Alpides, the products of the closure of the Paleo- and the Neo-Tethyan oceans, respectively. Paleo-Tethys was the oceanic realm that originated when the late Paleozoic Pangea was assembled by the final Uralide–Scythide–Hercynide–Great-Appalachide collisions. It was a composite ocean, i.e., not one formed by the rifting of its opposing margins, and its floor was already being consumed along both Laurasia- and Gondwana-Land–flanking subduction zones when it first appeared. The Gondwana-Land-flanking subduction systems, in particular, created mostly extensional arc families that successively led to various Paleo-Tethyan marginal basins, the last group of which was the oceans that united to form the Neo-Tethys. The Paleo-Tethys may have become an entirely continent-locked ocean through the construction, to the east of it, of a Cathaysian bridge uniting various elements of China and Indochina into an isthmian link between Laurasia and Gondwana-Land during the latest Permian, inhibiting any deep-sea connection between the Paleo-Tethys and the Panthalassa. That land bridge may have been responsible for the peculiarities in the distribution of the latest Permian-early Triassic Dicynodonts and possibly some brachiopods, benthic marine microorganisms, and land plants. The existence of the Cathaysian bridge seems to have helped the formation of anoxic conditions in the Paleo-Tethys. In fact, it seems that the major Permian extinctions began in the Paleo-Tethys and were really mainly felt in it and in areas influenced by it. This isolated setting of the Paleo-Tethys we refer to as a Ptolemaic condition, in reference to the isolated oceans Claudius Ptolemy had depicted on a geocratic Earth in his world map in the second century AD. Ptolemaic conditions are not uncommon in the history of Earth. Today, such a condition is represented by the Mediterranean and its smaller dependencies such as the Black Sea and the South Caspian Ocean. Para-Tethys in the Neogene had a similar but even more isolated setting. As we see in all these late Cenozoic cases, such Ptolemaic oceans have a major influence on the evolution of the biosphere. The Paleo-Tethys seems to have had a much larger impact than any of its successors owing to its immense size and may have been the key player in the so-called “end-Permian” extinction, which, in reality, was a mid to late Permian affair, with some late phases even in the earliest Triassic. The Permian extinction happened in at least two main phases, one in the Guadalupian and the other near the end of the Lopingian, and in each phase different animal and plant groups became extinct diachronously, phasing out according to the degree they were influenced by the developing anoxia within the Paleo-Tethys. What these conclusions suggest is that when investigating the causes of past events, regional geology must always form the foundation of all other considerations. Many speculations concerning the Permian extinction events cannot be adequately assessed without placing their implications into the geography of the times to which they are relevant. A purely “process-orientated” research that downplays or ignores regional geology and attempts to ape physics and chemistry, as is now prevalent in the United States and in western Europe and regrettably encouraged by the funding organizations, is doomed to failure.