Geochronology,Geochemistry And Geodynamic Significance Of The Dala Two-Mica Granite In Tethyan Himalaya,Tibet

There are a large number of Cenozoic leucogranites distributed in the Himalayan rogenic belt since the collision between the Indian plate and Asian plate. The issue concerning their petrogenesis and geological setting are one of the hottest ones among the Tibetan magmatism research. This dissertation reports the data of zircon U-Pb geochronology, bulk-rock major element, trace element and Sr-Nd isotopes of the Dala two-mica granites in Tethyan Himalaya, aiming to provide more petrology and geochemistry answers for these questions.Dala two-mica granites intruded into the Lower Paleozoic Qudegong low-grade metamorphic rocks and Late Triassic marine flysch sedimentary formation, is located to the southeastern of the Yalaxiangbo gneiss dome. Zircon U-Pb dating show the crystallization ages of 44 Ma, two samples yield similar protolith ages of 44.5±1.4Ma, 44.2±0.97 Ma.Dala two-mica granite has high SiO₂（70.73%⁷2.64%）, CaO（1.94%².67%）, Al₂O₃（15. 56%¹6. 9%）, Na₂O/K₂O ratios（average is 1.16）, and A/CNK（>1.0）, This suggests that the Dala two-mica granite belong to high calcium rich sodium strong peraluminous granite. It is obvious enrichment of Sr, Ba, Zr, loss of Y, Rb, Ta, Nb Shows a high Sr/Y characteristics, highly enriched in LREE and depleted in HREE, slightly no or negative Eu anomalies, Eu/Eu*（0.76⁰.96）, differentiation is more significant between MREE and HREE,（Gd/Yb）N（4.1⁶.2）.TZr is high（734℃ 769℃）, formation pressure is greater than 1000 Mpa,(⁸⁷Sr/⁸⁶Sr)（t） and Nd（t） are 0.717126⁰.718803 and-13.0^-10.5, imply the Dala two-mica granites are formed by partial melting of the lower crust basic material with the residual phase of garnet and the lower crust basic material may have contaminated by the enriched mantle of Indian continent, lower（Ho/Lu） N show amphibole is also one of the residual phase.Dala two-mica granites have a large number of surrounding rock captures,, age spectrum of the inherited zircon is consistent with the surrounding rock imply the Dala two-mica granites have apparently contaminated by upper crustal rocks. A series of intermediate-basic magmatic rocks occurs in the Tethyan Himalaya at the same time imply the Dala two-mica granite is formed by partial melting of the lower crust basic material under the condition of tectonic thickening because of the asthenospheric upwelling induced by Neo-Tethyan slab breakoff. The magma have contaminated by upper crustal rocks before emplacement.