Structure Of Crust-mantle Beneath Qiangtang Terrane And Interaction Model

Located in the northern Tibetan Plateau, Qiangtang Terrane is situated betweenthe Jinshajiang suture belt and Bangong-Nujiang suture belt．The terrane is dividedinto two section: the south and north by the central uplift. Geophysical data indicatethat the Qiangtang Terrane may be located in the front of the collision zone betweenthe Indian plate and the Asian plate, and the south-north compressive stress affects thedeep structure of the terrane. As a special production under a typical geologicalconditions within the uplifting of Tibetan Plateau, Cenozoic potassic and ultrapotassiclava in north Qiangtang Terrane was an important window to ascertain deep structureof the crust and mantle, which is also related to study geodynamic process of theTibetan uplifting and its geological correspondence for continent-continent collisions.After reviewing research history by geological and geophysical scientists in thisfield and the basic principle of receiver function and the H-κ stacking and CCPstacking methods, the author conducted a systematic receiver function analysis usinga total of high signal-to-noise ratio teleseismic traces recorded by54stations that weretemporarily deployed in the region and got information of Moho depth and Poisson’sratio by standard H-κ stacking and CCP stacking method. Then the author used twotechniques of isostatic correction and two-dimension density fitting to analyzebouguer gravity anomaly, and had got isostatic gravity anomaly and two-dimensionsstructure of density. At last, on the basis of analysis of isostatic gravity anomaly andthe receiver function, along with existing regional geology, tectonics, geochemicaldata and geophysical information, this paper has debated the structure of crust-mantlebeneath Qiangtang Terrane and interaction model. The results show that:(1) Longmuco-Shuanghu suture was tectonic boundary zone with the nature ofthe suture zone.South Qiangtang and North Qiangtang have great differences incrustal structure.South Qiangtang basin Moho depth is average63km and NorthQiangtang basin Moho depth is60km. Poisson’s ratios have harmoniously variedwith tectonic units,0.31in South Qiangtang,0.265in Shuanghu suture zone, and0.285in North Qiangtang, respectively.(2) Two steps exist in Moho topo beneath whole Qiangtang,10km Moho offsetbeneath BNS as south tectonic boundary of Qiangtang and3km offset of Mohobeneath central uplift belt. It may be the result of south-north compression in TibetanPlateau.Nearly horizontal layer topo of Moho beneath Qiangtang probably was causedof re-isostatic process resulted from northward subduction and injection of Indianplate.(3) The crust and upper mantle beneath North Qiangtang were in deficit statewith a lower density than other regions in Tibet. It is suggested that the sustainednorthward subduction of the Indian plate has resulted in breaking off of the frontalmargin of the Asian lithosphere mantle.