Chapter 4. Paleozoic granitoid magmatism of South and Middle Tien Shan in Uzbekistan

The Paleozoic evolution of the Southern and Middle Tien Shan terranes is generally associated with the history of two ocean basins - the Turkestan and Paleotethys. Ages of ophiolites indicate the opening of the oceans in Cambrian – Ordovician, and partial closure with formation of an island arc in the northern part of the basin in Ordovician - Silurian. At the northern margin of the Turkestan ocean, the northward subduction under the Middle Tien Shan continued until Devonian, which led to formation of an active margin with granitoids emplaced between 429 and 416 Ma. In the late Devonian, subduction-related magmatism terminated and the whole region developed as passive margin. Northward subduction resumed in the early Carboniferous and formed magmatic Andean-type belt exposed in the Chatkal-Kurama terrane. Late Carboniferous collision resulted in crust thickening and emplacement of postcollisional granitoids. Formation of postcollisional intrusions in different terranes took place in various tectonic settings. Shoshonitic granitoids of the Chatkal-Kurama terrane formed as a result of slab break off at postcollisional stage. Voluminous postcollisional magmatism of Kyzylkum can be explained by delamination of lower crust and its replacement by the material of astenospheric mantle. Coeval emplacement of geochemically contrasting granitoids in the North Nuratau fault zone could result from contemporaneous melting of different protoliths at different depths in a translithospheric shear zone.