Mesozoic replacement of bottom crust in North China Craton: anorogenic mantle-crust interaction.

The study of Precambrian granulite terrain in the North China craton and the granulite xenoliths in Cenozoic volcanic rocks shows that there are differences between the Precambrian lower crust and the present lower crust. This study further shows that the Mesozoic tectonic inversion in the North China craton not only causes changes in basin-range system but also changes in the composition and texture of the lower crust and upper mantle. There have been many models suggested, such as delamination,mantle-root structure etc, for the mechanism of thinning of the eastern lithosphere, all are related to the evolution of orogenic belt. We have noted in our work that most or all of the lowermost crust of the North China craton has been substituted by the Mesozoic lower crust. This has been occurred not only the edge of but also within the craton. Therefore, the processes of the North China craton mantle uplifting and the quick thinning of the Paleozoic lithosphere may be seen as the replacement of bottom crust in the North China craton. An upwelling mantle plume possibly existed during Jurrasic-Cretaceous, and strong crust-mantle interaction is a major way of replacement of bottom crust, while the details of thermal and chemical corrosion is still not clear. However, it may be inferred that this has no direct relationship with the evolution of orogenic belt and is different from the lithosphere delamination at the root of orogenic belt.