Abstract: The Fuling pluton is located in the eastern section of the Jiangnan orogenic belt and is a typical highly differentiated granitic complex pluton in southern Anhui. In this paper, petrographic, mineral microbeam analysis (including electron microprobe and LA-ICP-MS) and trace element simulation calculations were carried out to study the K-feldspar in the granite of the Fuling pluton. The K-feldspar analysis shows that the K-feldspar $ m(\mathrm{K})/m(\mathrm{Rb}) $ ratio gradually decreases, the mass fractions of Rb and Cs gradually increase, and the mass fractions of Sr and Ba gradually decrease from Kfs-I, Kfs-II to Kfs-III. K-feldspar compositions (including K, Rb, and Cs) were used to simulate magma crystallization evolution, and the results show that Kfs-I and Kfs-II can be formed from the initial melt after 0-90% fractional crystallization, indicating that fractional crystallization plays an important controlling role in the evolution of the Fuling pluton, while the most evolved Kfs-III requires the initial melt to undergo fractional crystallization exceeding 95% to form, but the granitic melt is difficult to undergo such a high degree of fractional crystallization. When the melt is saturated with $ H_{2}O $ and the fluid exsolution occurs, the exsolution fluid will be significantly enriched in Pb. Since Ba has a low fluid-melt partition coefficient, the exsolution fluid will be enriched in Pb, while losing Ba, and the extremely high $ \omega(\mathrm{Pb}) $ and extremely low $ \omega(\mathrm{Ba}) $ of Kfs-III indicate that it was formed by fluid-melt interaction. Therefore, the enrichment of rare metal elements in the Fuling pluton is not solely controlled by magmatic evolution; the late fluid exsolution may be an important process causing the extreme enrichment of rare metal elements.
Keywords: complex pluton; geochemistry; K-feldspar; Rayleigh fractionation modeling
合肥工业大学学报自科版