关键词: 花岗岩成因, 地球化学特征, 锆石U-Pb定年, 早古生代早期, 江西付坊

Abstract:

The Fufang granitoid pluton, outcroped in the middle part of Wuyi Mountain area, is a typical Early Paleozoic pluton in the eastern segment of South China. Based on large amount of geological data during regional geological survey, the authors carried out a systematic study on petrography, geochemistry and LA-ICM-MS zircon U-Pb dating for the Fufang pluton. This pluton is mainly composed of monzogranite, granodiorite and in less amount tonalite containing Al-rich mineral, such as garnet and sillimanite. The A/CNK values are 0.99~1.14, categorized as weakly peraluminous and strong peraluminous. In trace elements, the Fufang pluton is enriched in LILE Rb, Th, Cs and rare earth elements La, Ce, Nd, and depleted in Ba, Sr, Ta, P, Ti. Thus, the Fufang pluton is a low Ba-Sr granite on the whole. The Rb / Sr and Rb / Nb ratios are 0.56~1.19 (everaging 0.92) and
6.85 ~25.18 (everaging 15.43), respectively, higher than the average values of the upper crust in eastern China and the world. The Fufang pluton has a higher ∑REE with LREE enrichment. Their distribution patterns are clearly right-wing type with relatively clear Eu depletion (δEu = 0.44~0.61, averaging 0.53). The emplacement ages of the pluton obtained for zircons from 1 sample of granodiorite and 2 samples of monzogranite are ( 443.9 ± 3.5) Ma (MSWD = 1.09) , (443.1 ± 4.6) Ma (MSWD = 0.25) and (433.6±3.9) Ma （MSWD = 0.61）, respectively. The first two sets of data are consistent ages within error range which shows that they were resulted from the differentiation and evolution of a co-magmatic chamber. The later one is obviously later and belongs to the later stage of the Early Paleozoic. The research results show that the Fufang pluton is of S-type granite, derived from the continental crust by lower degree of partial melting and its source rocks were mainly composed of pelitic sandstone rocks. The formation was probably linked with the collision between the fragments of Cathaysia Old Land and Yangtze block or collision among the fragments of Cathaysia Old Land. The earlier granitoids of Fufang pluton were syn-orogenic, formed in a compression environment, while the later granitoids were origined in a post-orogenic extension environment.

Key words: granite genesis, geochemical charteristics, zircon U-Pb dating, Early Paleozoic, Fufang, Jiangxi province