Uplift－Geodynamic Model Of The Southeastern Margin Of Tibetan Plateau (Shangri－La): Geochemistry And Thermochronology

After a detailed field investigation, we study the petrology, element geochemistryand zircon U－Pb geochronology characteristics of the two different types Indosinianintrusive rocks in order to know their genesis and deep geodynamic background; At thesame time, we study the thermochronology of the representative strata and Indosinianintrusive rocks and discuss their uplift－erosion processes. At last, a simplifiedgeodynamic model of crustal uplift of southeastern margin of Tibetan Plateau isproposed.1. Detailed field investigation show that strong deformation, such as recumbentfold, suggesting that compression contributes to the crustal thicken, which is limited inthe west Himalaya tectonic knot.2. Researches of the two different types Indosinian intrusive rocks reveal that theyderived from a similar magma resource and grew to be different types. Later softmelt/magma－fluid pulse affected the A’re quartz diorite porphyry while the Beng’gelamprophyre－alkaline complex group were influenced and reconstructed morefiercely, and this is because that beneath the Beng’ge lamprophyre－alkaline complexgroup is the mantle sag was sharply changed to be mantle upheaval which may inducemass and energy exchange actively. The complexity of Beng’ge amprophyre－alkalinecomplex group was enhanced by the interaction between mantle upwelling and lowercrustal channel flow. Judging from a large and macroscopical view, geochemicalfeatures of the majority of the intrusive rocks along the Jingshajiang－Ailaoshan deepfault are similar which implies that deep geochemical reservoir of the correspondingmagmatic rocks are influenced by mantle－crust transition zone.3. Fission tracks of apatite and zircon and temperature－time modeling exhibitedtwo uplift processes. The first one was recorded by ZFT which happened in theCretaceous Era and related to the mantle upwelling and thermal effect. The second onewas recorded by AFT which happened in the Cenozoic Era and controlled by thecompression－shorten deformation process and block slip and rotation process. Estimation of the erosion velocities indicate that the uplift velocities of Zhongzan－Zhongdian Block were fast than Yidun Island Arc and Yangtze Block, and further more,the Yidun Island Arc was uplifted gradually from northern to southern.4. A simplified geodynamic model of crustal uplift of southeastern margin ofTibetan Plateau is proposed. During the subduction of Indian Plate and Yangtze Plate,under the combined operations of northeastern tectonic shorten, mantle upwelling andlower crustal channel flow, the crust of research area was uplifted heterogeneously andmultistage. We think that the lower crustal channel flow contributed more than the twoothers, while the stabilization of deep thermal structure was maintained by mantleupwelling. Although we do not estimate the crustal thickening extent caused bytectonic compression process, the strong deformation of strata implies that tectoniccompression may leads to superposition of the cortical crust or upper crust, andmeanwhile the mantle upwelling and lower crustal channel flow mainly acted on thelower crust.