The largest mountain belt in Central Asia (similar to 9 million km(2)) is called the Altaids. It was assembled between similar to 750 and similar to 130 Ma ago around the western and southern margins of the Siberian Craton, partly on an older collisional system (the "Urbaykalides"). Geological, geophysical, and geochemical data-mostly high-resolution U-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 total. The Altaids thus added some 3 million km(2) to the continental crust over a period of 0.6 billion years, typical of Phanerozoic crustal growth rates.