Abstract: The Mesozoic Baishitouquan (BST) topaz-bearing amazonite granite pluton has been dated at 209.6±9.6 Ma by the Rb-Sr isochron method. This pluton exhibits five lithological zones, which, gradational from the lowest level upwards, are leucogranite (zone a), amazonite-bearing granite (zone b), amazonite granite (zone c), topaz-bearing amazonite granite (zone d) and topaz albite granite (zone e). Geochemically, The rocks are characterised by higher F (>2%) and Rb (500~1087×10-6), lower P2O5 (≤0.06 %), Na2O>K2O, A/NKC=1.00~1.11, Σ14 REE=28.6~231.9×10-6 with gull wing-shaped distribution patterns (LaN/LuN=0.11~0.68) and strong Eu depletion (Eu/Eu* =0.0005~0.0110). δ18O=9.75~7.32 ‰, εNd (t )= -4.4~-4.9. The magma for this pluton was derived by partial melting of a mica gneiss in the middle crust. The pluton exhibits the following geochemical transition from zone a to zone e: 1) Increasing F, Al2O3 and Na2O, and decreasing SiO2, (Fe2O3+FeO+MgO+MnO) and K2O. Plots of normative compositions on the Qz-Ab-Or diagram move gradually towards the Ab apex. 2) Overall, contents of Cr, Ni, Co, V, W,Nb, Zr, U, Th and Y decrease, while contents of F, Li, Rb, Hf, Ta, Sn, Sc, Ga and Zn increase. 3）K/Rb, Al/Ga, Nb/Ta and Zr/Hf decrease, and K/Cs, Th/U, and (La/Lu)N increase; 4) Whole-rock δ18O decreases from 9.25~9.75‰ in zone a to 7.32‰ in zone e. It is interpreted that crystallisation of the magma started from zone a and proceeded upwards to zone e, and the vertical zoning was produced by fractional crystallisation accompanied by fluid fractionation. There is a compositional gap on the transition trend between zone d and e. This gap is manifested in mineralogy by sharp increase in topaz, albite and muscovite and decrease in K-feldspar and amazonite; in major elements by sharp increase in Na2O and CaO and decrease in SiO2 and K2O; in trace elements by sharp increase in F, Ga, Sr and Ba, and sudden decrease in Li, Rb, Sc, Zn and Sn; in REE behaviour by sudden increase in Eu/Eu* and （La/Lu）N, and decrease in ΣREE; and in isotope composition by sharp decrease inδ18O. Such a gap might have been constrained not only by fractional crystallization and fluid fractionation, but also by involvement of meteoric water, contamination of wallrock-derived components, and leaching and dispersion due to subsolidus metasomatism.