五台山地区前寒武纪花岗岩类的稀土元素地球化学

REE GEOCHEMISTRY OF PRECAMBRIAN GRANITOIDS IN WUTAISHAN REGION

本区前寒武纪花岗岩分五台早期和晚期两类,皆有太古宙花岗岩的共同特征。从早期的钠质花岗岩到晚期钾质花岗岩,其REE丰度增加,变化规律受钾、钠和铝的控制。其源岩物质可能源于上地壳岩和玄武质岩石。

Conspicuous Archaean REE geochemical characteristics are noticed for the Precambrian granitoids in the Wutaishan region. The REE abundances of the granitoids show a progressive increase from the early to the late Wutai stage. For example, the REE abundances of potassic granitoids are higher than those of soda-granites and of high-Al granites are much lower than those of low-Al equivalents. Three types of REE distribution patterns have been distinguished: (1) rightward declined smooth curves, showing no obvious Eu anomaly (Eu/Eu* = 0.74-0.82) and high fractionation (granodiorite-quartz monzonite); (2) moderately rightward declined curves, displaying remarkable positive and negative Eu anomalies (Eu/Eu* = 1.24-1.62 -0.83) and a minimum total REE content (high-Al and low-Al tonalitetrondhjemite); and (3) rightward declined V-shape curves with a maximum content of REE (granites). These granitoids are considered to have resulted from partial melting and differentiation, and their parent materials may be originated from upper crust rocks and basalts.