Teleseismic Tomography Based On Non-uniform Grids In The Center-east China And Its Implication

There are abundant geological structures and mineral resources in the center-east China, which have made the area become a hot research topic in the field of geology. In order to understand the deep dynamic processes and magmatic activities in the center-east China better, this paper developed a new teleseismic tomography method which bases on non-uniform grids. 13687 S-wave relative traveltime residuals are obtained through the cross correlation method using the records from 141 fixed stations and 72 temporary stations which recorded 283 teleseismic S-wave events; 32728 P-wave relative travel time residuals is obtained through the cross correlation method using the records from 154 fixed stations and 72 temporary stations which recorded 479 teleseismic P-wave events. We used a theoretical model and the actual data to verify the reliability of our method and to determine the appropriate parameters of our inversion. From the inversion we got the 3-D S-wave and P-wave velocity structure of the study area down to a depth of 700 km, we also calculated the Poisson’s ratio( σ) anomaly by using the velocity structure.From the inversion results, it was found that there was a good consistency between the S-wave velocity’s anomaly and the P-wave velocity’s anomaly, and the Poisson’s ratio anomaly was consistent with the distribution of the two anomalies too. Specifically, we found two different depth of high velocity and low Poisson’s ratio anomalies in the eastern part of China. By reference to a large number of literatures, this study explained them for the demolition of the lithosphere and the subduction of the Pacific slab respectively; At the same time, the study found that there was an obvious low velocity anomaly within the upper mantle beneath the study area, and the Poisson’s ratio anomaly was high, the anomaly was interpreted as the upwelling hot mantle material.Combined with a large amount of geological, geophysical and geochemical data, this study argues that(1) during the Palaeozoic era, the North China Cartoon(NCC) combined with the South China Block(SCB) after a series of tectonic movements, the processes formatted the Qinling- Dabie orogenic belt and made the SCB subduct under the NCC, the form of the subduction was presented shallower in West. At the same time, the combination formatted the first batch of ultrahigh pressure metamorphic rocks of the Qinling- Dabie orogenic belt.(2) In the period of the Mesozoic, the Pacific slab began to subduct under the eastern part of China. At the first, the plate subduction’s angle was small and the angle became steep in the Jurassic period, the angle might be different under the NCC and the SCB, as a result a subduction window was produced between the NCC and the SCB.(3)The subduction of the Pacific slab caused stress environment to change and large-scale mantle material to upwell in the east-central China, which eroded the lithosphere. During the early Cretaceous period, the East Qinling – Dabie orogenic belt, middle and lower Yangtze region occurred lithospheric delamination, and with the Mesozoic Magmatic activities, the middle-lower Yangtze River metallogenic belt was formed.