关键词: 碱长花岗岩, 造山后, LA-ICP-MS U-Pb定年, 赣中

Abstract: Fine-to medium-grained two-mica alkali-feldspar granites hosting tungsten and molybdenum minerals occur in the
Dawangshan tungsten polymetallic ore field in central Jiangxi Province. LA-ICP-MS U-Pb dating of zircon from Dawangshan
ore-bearing granites yields an age of 147.8±1.9 Ma, which indicates Late Jurassic time. The intrusion of the granites as evidenced by
the U-Pb age, coincided with the ore-forming of the quartz-vein type tungsten polymetallic deposits in central Jiangxi Province and
Nanling area. The granites are strongly peraluminous with high differentiation index (DI) and contain minor dark minerals. The granites
are enriched in alkali and silicon, and are depleted in calcium and magnesium. The REE partition curve shows a“seagull pattern”.
Their primitive-mantle normalized trace element spidergrams indicate depletions in Ba, Sr, Nb, Eu, P and Ti, and enrichment in Rb,
Th, U, Pb and K. In the diagram of εNd(t) vs. T, the granite samples are projected in the area between the Proterozoic crustal region of
South China and the chondrites mantle, suggesting a source from mantle source material. The results of the T2DM ages of granites (1.39~
1.66 Ga) are relatively younger than the average age of the crust in South China (1.7~1.8 Ga). These indicate that the formation of
granites likely involved a small amount of mantle materials. By combining the Sr-Yb and Q-Ab-Or diagrams as well as the calculated
zircon saturation temperatures, we conclude that the granites belong to high-differentiated peraluminous S-type granite and they were
formed in a post-orogenic extensional environment with low temperature, low pressure and water-rich conditions.

Key words: alkali-feldspar granite, post-orogenic, LA-ICP-MS U-Pb dating, central Jiangxi Province