Age, composition, and tectonic significance of Palaeozoic granites in the Altyn orogenic belt, China

The north Altyn region saw a change from subduction to collision between the Dunhuang block and the NAB during 467–450 Ma. The collision lasted until 430 Ma and was followed by post-collisional extension until 400 Ma. Farther south, the central Altyn Ocean subducted northwards beneath the CAB, resulting in 520–500 Ma granitic magmatism and leading to collision of the south Altyn micro-block (SAMB) with the CAB.

Deep subduction of SAMB crust below the CAB resulted in granite intrusions during 490–455 Ma. The SAMB–CAB collision gave way to post-collisional extension, slab break-off, and delamination during 450–430 Ma. Bidirectional subduction of the south Altyn Ocean after ~485 Ma, dominated by southward subduction, continued until 456 Ma.

Closure of the south Altyn Ocean led to continent–continent collision between the SAMB and the Qaidam block at 450–430 Ma, followed after ~410 Ma by repeated break-offs of slab segments until 337 Ma. Subsequent intrusions formed at 264–226 Ma in a setting of either post-collisional extension or sinistral strike-slip.