WU Ji-cheng, LI Ji-hua, LI Tai-bing, LI Yong-guang

Gold Technology College, Chinese People's Armed Police, Xiangfan, Hubei 441002, China

Abstract:　  The Nacheng granite locates in the Yongning area, Guangdong Province. This paper studied petrographical and chronological characterist ics of this granite as well as it s petrogenesis and geological significance. The Nacheng granite mainly consists of quart z ( 40% ~ 50%) , orthoclase ( 25%~ 30%) , palgioxlase ( 15% ~ 20%) with minor accessory minerals of quartz apatite and magnetite. Geochemical analyses show that the manziying granite has high content of SiO₂ ( 75. 56%) , K₂O ( 4. 72%) , Al₂O₃( 13.34%) and total alkali ( Na₂O+ K₂O= 7. 49%) , but relatively low MgO ( 0. 04%~ 1. 29%) and CaO ( 0. 39% ~ 2. 21%) . The ratios of K₂O/ Na₂O are generally higher than 1. The Rittmann indexes are between 1~ 2. 43, belonging to the high-K calc-alkaline series. The values of A/CNK vary from 1.12 to1.32 with an average of 1.10, showing the aracteristics of peraluminous S type granites. Trace element analyses show that the Nacheng granite has relatively high REE content of 82.6x10^{- 6}~ 225.68x10^{- 6}, and displays right-inclined V-shape REE patterns with relatively high fractionations of LREE and HREE[ ( La/ Yb) N= 1. 51~ 9. 66] and pronounced negative Eu anomalies ( δEu= 0.31~ 0.74) in the chondrite-normalized REE diagrams, suggesting a typical crust-derived grandite. The magmas may be divided into two types: " low-temperature" type from mudstones and "high-temperature" type from sands tones. The Nacheng granites were formed from the post-orogenic tectonic setting.

Key words:   S-type granite; syn-collisional; peraluminous; geochemistry; Guangdong Province 

*Corresponding Author, E-Mail: wjcyoujian@yahoo.com.cn

Bulletin of Mineralogy, Petrology and Geochemistry Vol. 29, No.4, 2010, page 364-372

(Source from http://www.cnki.com.cn/)