Detection of the low velocity layer atop the 410-km discontinuity beneath Northeast China with Slowness based CCP stacking
Master of Science
The structure and tectonics of Northeast China are dominantly affected by the interactions of Pacific plate and Eurasia plate. The mantle transition zone (MTZ) structures are also influenced due to this interaction. The importance of the MTZ in advancing understanding of mantle dynamics is highlighted by the Transition Zone Water Filter (TZWF) model, which predicts the existence of a partial-melt layer atop ‘410’, hereafter referred to as 410-LVL (Low Velocity Layer). In recent years, efforts to investigate the 410-LVL are accelerating. Regardless of the veracity of the TZWF model, it is clear that a more complex role for the MTZ in thermochemical mantle convection is emerging and that higher resolution seismic mapping of lateral variations in mantle layering will provide valuable constraints on the thermal and chemical processes active in the MTZ. The presence of a global layer of partial melt above the ‘410’ discontinuity would modify material circulation in the Earth mantle and may help to reconcile geophysical and geochemical observations. We collect the data in Northeast China mainly from NECESSArray and CEArray. By first screening the raw data and then generating the receiver functions from the selected data, we are able to use the common conversion point (CCP) method to do the stacking of the receiver functions. After the stacking, the common features will emerge. However, we are not clear whether some of the features are real structures or processing artifacts. We introduce the slowness based CCP stacking method to further confirm the existence of 410-LVL. With additional support from the statistical analysis of the results, we are able to finalize the detections of the 410-LVL. The LVL is not related to a particular type of geodynamical environment atop the ‘410’: it is found globally with various geological settings. The NE China area is dominantly affected by the subduction of Pacific plate under Eurasia plate. The stagnant slab has the ability to add a large amount of subducted fluid into the mantle. Slab dehydration creates the 410-LVL, along with the potential for subsequent triggering of wet mantle upwelling.