| The continuous Indo-Eurasian collision since ?50Ma has resulted in a crustal shortening of at least 1500 km in the suture zone,and such a large crustal shortening is thought to have been absorbed along a series of large strike-slip faults.In the early stage of suture,the Indo-Chinese blocks were considered to be extruded from the eastern part of the Qinghai-Tibet Plateau,so the Indo-Chinese blocks became an ideal area to verify the evolution mechanism models of different uplift mechanisms of the Qinghai-Tibet Plateau and understand the process of plate movement.Located in the north of the Indo-Chinese block,Tengchong volcanic area(98°15‘-98°45‘E,24°40‘-25°30‘N).Volcanoes in Tengchong Volcanic Area are widely distributed and formed by volcanic eruptions in different periods.According to Xu Xiake's travel notes,there was a small volcanic eruption in Tengchong in 1609 and the volcano may still erupt in modern times.Therefore,the study of the lithospheric velocity structure under the Indo-Chinese block is of great significance for revealing the volcanic activity,the origin of hot matter and the mechanism of crust-mantle deformation in Tengchong.In this paper,we select the broadband three-component data from 148 stations on the Indo Chinese block.After deconvolution,we obtain the remote P-wave reception functions below the stations.From these,we select 2859 good P-wave reception functions,and use them to combine surface wave dispersion to invert the crust-mantle S-wave velocity structure on a 0.5 ×0.5° grid in the study area.In order to effectively constrain the nonuniqueness of inversion,a two-step inversion technique is adopted in this paper.In the first step of inversion,a single low-frequency receiver function(Gaussian parameter 1.0)was used to jointly invert the surface wave,and the bootstrap resampling technique was used to statistically analyze the inversion results,and an optimal solution was obtained.In the second step of inversion,a single high-frequency receiver function(Gaussian parameter 2.5)was used to jointly invert with surface waves.The Bootstrap resampling technique was also used to conduct statistical analysis on the inversion results,and the average result was taken as the final result.In the inversion process,we have completed the joint inversion of Rayleigh wave and receiver function,Love wave and receiver function,and both of them and receiver function.The main research work and results of this paper are as follows:The inversion results show that the joint inversion with Rayleigh wave,luff wave and P wave receiver functions can effectively constrain the nonuniqueness of the inversion,and is more effective than the joint inversion with Rayleigh wave and P wave receiver functions.By using a single receiver function,the information contained in each receiver function is fully exploited.In addition,the Bootstrap resampling technique provides a more reliable result.The middle and upper crust of the Lanping-Simao block(0?16km)has a low S-wave velocity in the Simao-Yuanjiang block,which may be caused by the shear heat generation of the Honghe fault and the upwaging of mantle magma.Near Dali,there is a low-velocity layer in the shell with a thickness of about 10 km at a depth of 15-25 km,which is consistent with the location of strong earthquakes.There are obvious high velocity layers near the surface of Tengchong Volcanic Area.It is speculated that the high velocity is caused by the deposition and solidification of hot mantle material after volcanic magma eruption.However,from about 16 km away,the high velocity layer gradually disappeared and the low velocity zone appeared in the middle and lower crust,which may be caused by the magma upwelling caused by the eastward subduction of the Myanmar microplate.However,in the upper mantle beneath the Tengchong volcanic area,the low-velocity zone is not obvious.The large scale low speed area appears under the Baoshan block on the east side of Tengchong volcanic area,with the maximum burial depth of about 80?90km.Therefore,it is inferred that the hot materials of Tengchong volcano may originate from the upper mantle under Baoshan volcano,rather than the upper mantle directly under Tengchong volcano,and these hot materials were transported westward to the top of the upper mantle of Tengchong volcano.Low velocity zones are common in the crust of the entire Indo-Chinese block,which may be caused by the Indian plate subducting under the Burma arc,which dehydrates the high velocity plate and causes a large amount of wet and hot material to surge up from the mantle transition zone and into the crust along some deep faults. |
PDF Full Text Request