(Hf) isotope analysis, xenolith zircon studies, and analysis of the metamorphic rocks. Causes of craton destruction The causes of the craton destruction event and the thinning of the Eastern Block lithosphere are complicated. Four models can be generalized from the different mechanisms proposed by scientists. Subduction Model This model explained subduction as the main cause of the craton destruction. It is a very popular model. Subduction of oceanic plate also causes subduction of water inside the lithosphere. As the fluid encounters high temperature and pressure when being subducted, the fluid is released, weakening the crust and mantle due to the lowered melting point of rocks. Subduction also causes the thickening of crust on the over-riding plate. Once the over-thickened crust collapses, the lithosphere would be thinned. Subduction causes the formation of eclogite because rocks are under high temperature and pressure, for example, the subducted plate becomes deeply buried. It would therefore cause slab break-off and slab rollback, thinning the lithosphere. Subduction was widely occurring in the Phanerozoic, including subduction and closure of Paleo-Asian Ocean in Carboniferous to Middle Jurassic, subduction of the Yang Tze Craton under the North China Craton in Late Triassic, and subduction of Paleo-Pacific Plate in the Jurassic and the Cretaceous as mentioned in the previous part. The subduction model can therefore be used to explain the proposed craton destruction event in different periods. Extension Model There are 2 types of lithospheric extension, retreating subduction and collapse of orogens. Both of them have been used to explain lithospheric thinning occurred in the North China Craton. Retreating subduction system means that the subducting plate moves backward faster than the over-riding plate moves forward. The over-riding plate spreads to fill the gap. With the same volume of lithosphere but being spread to a larger area, the over-riding plate is thinned. This could be applied to different subduction events in Phanerozoic. For example, Zhu proposes that the subduction of Paleo-Pacific Ocean was a retreating subduction system, that caused the lithospheric thinning in the Cretaceous. Collapse of orogen introduces a series of normal faults (e.g. bookshelf faulting) and thinned the lithosphere. Collapse of orogens is very common in the Cretaceous. Magma Underplating Model This models suggests that the young hot magma is very close to the crust. The heat then melts and thins the lithosphere, causing upwelling of young asthenosphere. Magmatism was prevalent throughout the Phanerozoic due to the extensive deformation