Researching Into Seismic Tomography And Mantle Convection

The delineation of global-scale three-dimension structure in the Earth's mantle has made rapid progress over the past a few years. Based on the newest third generational tomography, we can promote geodynamic largely. As the frame of mantle structure described by three-dimensional fine and lateral heterogeneity are the current representation of thermal-dynamic mantle evolvement and we can use it to cast back the evolvement history of mantle structure. The model of tomography can show the phenomena of slab diving and upwelling, so it is important to attain the trend and velocity of mantle flow based on tomography. In this paper, we describe a recently obtained model of 3-D compressible velocity of heterogeneity, called PMEAN, which shows striking examples of plume-like and whole mantle wide features characteristic of thermal convection flows. We take use of the newest highly-resolution tomography PMEAN and the data related to mantle convection, such as geiod, horizontal divergence of plate motion, dynamic topography and dynamic core-mantle boundary, we attain the pattern of mantle convection for whole global and east-Asia and western Pacific at last. Some important fruits and understanding are resulted from the imagines of vertical velocity of mantle flow for whole global and east-Asia and western Pacific.1. In view of there being two thermal layers at transition between upper and lower mantle and near CMB, we modify our viscosity model which is lower in these two regions.2. We find the trends between various calculated and observed mantle convection-related variable are roughly alike. Both type of geiod height are low at South America, Siberia, India Ocean and Antarctica, and high at Indonesia, Africa. As for dynamic topography, both show a clear pattern of elevated mid-ocean ridges and striking topographic depressions centraled on the ancient continental shields.3. There are roughly three super cold mantle plume: one is from Eurasia to Australia, the range of downwelling is narrower with depth, Among the tethyan region of Mediterranean Sea to Himalayas to Indonesia is obverse in the depth of 500-1000km and disappears at about 2000km; the other is beneath North-America to South-America which is also agreed with the FRALLON slab diving into lower mantle; the third is Antarctica down-plume which is obvious in the lower mantle. The three upwelling warm plume are respectively Western Indian Ocean to South Africa, the Pacific warm plume and Atlantic super warm plume, all of these are consistent with the occurrence of ocean mid-ridge.4. There is a upwelling plume beneath East-Asia and Western Pacific which is Earth's deep origin for huge rift valley here put forward by Pro. jieshou Zhu; Siberian clod downwelling is from surface dive to near CMB; the tethyan diving region centred in Qinghai-Tibet Platean is visible from 300km to 2000km. The three regions of Mantle convection beneath East-Asia and Western-Pacific is agree with Western-Pacific, Asia and tethyan structure regions.5. The pattern of mantle convection in whole global and East-Asia is controlled by whole mantle wide convection.Based on these, we can realize the exchanging form of matter and energy, and provide an important basis data for investigating nature, energy source, disaster and environment.