How long can the middle crust remain partially molten during orogeny?

Extensive partial melting of the middle to lower crustal parts of orogens, such as of the current Himalaya-Tibet orogen, significantly alters their rheology and imposes first-order control on their tectonic and topographic evolution. We interpret the late Proterozoic Aracuai orogen, formed by the collision between the Sao Francisco (Brazil) and Congo (Africa) cratons, as a deep section through such a hot orogen based on U-Pb sensitive high-resolution ion microprobe (SHRIMP) zircon ages and Ti-in-zircon and Zr-in-rutile temperatures from the Carlos Chagas anatectic domain. This domain is composed of peraluminous anatexites and leucogranites that typically exhibit interconnected networks of garnet-rich leucosomes or a magmatic foliation. Zirconium-in-rutile temperatures range from 745 to 820 degrees C, and the average Ti-in-zircon temperature ranges from 712 to 737 degrees C. The geochronologic and thermometry data suggest that from 597 to 572 Ma this domain was partially molten and remained so for at least 25 m.y., slowly crystallizing between temperatures of -815 and >700 degrees C. Significant crustal thickening must have occurred prior to 600 Ma, with initial continental collision likely before 620 Ma, a time period long enough to heat the crust to temperatures required for widespread partial melting at middle crustal levels and to favor a channel flow tectonic behavior.