Cretaceous igneous activity and tectonic evolution of the northeast Asia including the Korean Peninsula

The Cretaceous mafic and intermediate rocks in the Korean Peninsula have high Ti/V and Zr, indicating that they formed in a within-plate tectonic setting. The Cretaceous felsic igneous rocks show trace element compositions comparable to I and A2 type granites. These geochemical features are similar to those of Cretaceous igneous rocks in the northeastern North China Craton (NCC) and the southeastern South China Craton (SCC). It may suggest that the Cretaceous igneous activity in the Korean Peninsula occurred by extension, caused by slab roll back of the paleo-Pacific plate as in the NCC and SCC. The age of extension-related Cretaceous rocks in northeast Asia became younger towards the southeast, from 145-140 Ma in the northwestern area of the NCC to 117-84 Ma in the Korean Peninsula. On the other hand, the Cretaceous igneous rocks in Japan formed in the volcanic arc tectonic setting and started from 128 Ma. These indicate that the extensional stress due to a trench retreat disconnected the subducted oceanic slab in the location between the Korean Peninsula and Japan and then the subduction angle of the oceanic slab under the Japan increased with an initiation of arc-related Cretaceous igneous activities in Japan at ca. 128 Ma. Later, the Cretaceous igneous activities in southwest Japan became younger northward from 128 Ma to 65 Ma. This trend may be caused by a decrease in subduction angle and may have caused am-related igneous activities in the southern margin of the Korean Peninsula including the Gyeongsang Basin after 80 Ma.