The Altaids: A review of twenty-five years of knowledge accumulation

The Altaids is the largest orogenic belt in Central Asia occupying some ~9 million km². It is a Turkic-type orogeny assembled between ~750 and ~ 150 Ma around the western and southern margins of the Siberian Craton. All available data published so far, geological, geophysical, and geochemical—mostly high-resolution U[sbnd]Pb ages—document the growth of only three arc systems in Central and Northwest Asia during this time period, an interval throughout which there were no major arc or continental collisions in the area. While the Altaids were being constructed as a Turkic-type orogen, continental crust grew in them by 1/3 of the global average. The Altaids thus added some 3 million km² to the continental crust over a period of 0.6 billion years, typical of Phanerozoic crustal growth rates. The methods of reconstruction employed in elucidating the history of the Altaids are shown to be useful also in late Precambrian orogens built by ordinary plate tectonic processes, but contain no index fossils to erect a biostratigraphy. They also show that without a detailed knowledge of the strain histories of orogenic belts soldering different continental entities, no reconstruction can be even approximatley correct.