摘要
为了查明江西赣州隆木花岗岩形成时代及演化过程,对隆木岩体中的黑云母花岗岩与似斑状黑云母二长花岗岩进行LA-ICP-MS锆石U-Pb定年和同位素地球化学研究。结果表明:黑云母花岗岩与似斑状黑云母二长花岗岩的锆石U-Pb定年结果分别为(457±6)、(450±9)Ma,表明岩体形成于晚奥陶世;岩体铝饱和指数为1.11～1.29,K2O与Na2O含量(质量分数)之比为0.97～1.51,属强过铝质及高钾钙碱性岩石;根据ACF图解,岩体投影于S型花岗岩区域内;岩体Rb、Th+U、La+Ce、P、Nd、Zr+Hf+Sm相对富集,而Ba、Nb、Sr、Ti相对亏损,总体上属于低Ba、低Sr的花岗岩;岩体Rb与Sr含量之比为0.60～2.82,平均值为1.68,明显高于大陆地壳与上地壳的平均值,具壳源花岗岩特征;根据A/MF-C/MF图解,岩体物源区为砂质岩;岩体稀土元素含量总量偏低,为(113～176)×10-6,轻稀土元素富集明显,配分模式明显呈右倾型,Eu异常为0.38～0.67,Eu亏损程度中等偏高;化学成分显示,岩体属于强过铝质高钾钙碱性S型花岗岩,是一种壳源花岗岩,岩浆源区为成熟上地壳的砂质岩源区;构造判别图解、年龄信息及野外特征表明,岩体形成于后碰撞伸展构造环境。总之,隆木岩体形成于早古生代晚期的加里东构造运动,是华夏古陆块与扬子古陆块在新元古代碰撞拼贴之后裂解、在中奥陶世再次发生陆内碰撞使得地壳加厚部分重融、造山后期地壳伸展减薄、熔融物质上升侵位形成的岩体。
In order to find out the formation age and evolution process of Longmu Granite in Ganzhou of Jiangxi Province, LA-ICP-MS zircon U-Pb dating and isotope geochemistry of biotite granite and like-porphyritic biotite monzogranite in Longmu Pluton were studied. The results showed that the ages of zircon U-Pb dating of biotite granite and like-porphyritic biotite monzogranite were （457±6）Ma and （450±9）Ma respectively, which indicated that the pluton emplaced in Late Ordovician; aluminum saturation index was 1. 11-1. 29, the ratio of contents （mass fractions） of K20 and Na20 was 0. 97-1. 51, so the plutons were categorized as strong peraluminous and high potassium calc-alkaline; according to the ACF diagram, the pluton was plotted in the field of S-type granite; Longmu Pluton was enriched in Rb, Th-I-U, Laq-Ce, P, Nd, Zrq-Hfq-Sm and depleted in Ba, Nb, Sr, Ti, so the pluton belonged to the granite with low Ba and Sr on the whole; the ratio of contents of Rb and Sr was 0.60-2.82 with an average of 1.68, which was higher than the average of continental crust and supracrust, so the pluton was categorized as crustal derived granite; according to the A/MF-C/MF diagram, the provenance of pluton was psammite; the content of rare earth element of pluton was lower （（113-176））〈 10-6） , the enrichment of light rare earth element was significant, the distribution pattern was significantly right-wing type, and Eu anomaly was 0.38-0.67 and the depletion was more than middle; chemical composition showed that the pluton was S-type strong peraluminous high potassium calc-alkaline granite which was a kind of crustal derived granite, and magma protolith was the psammite source of mature supracrust; the tectonic discrimination diagram, zircon U-Pb dating and field characteristics indicated the pluton emplaced in a post-orogenic extension environment. In general, the emplacement time of Longmu Pluton was the late of Early Paleozoic under the control of Caledonian Movement; Cathaysia Plate and Yangtze Plate collided in Neoproterozoic and then cracked, and in the middle of Ordovician, the two plates happened intracontinental collision again which thickened the crust, and in post-orogenic stage, the crust began to strongly extension and partial melting and formed the mantle crust granite.
出处
《地球科学与环境学报》
CAS
2012年第3期44-56,共13页
Journal of Earth Sciences and Environment
基金
中国地质调查局项目(基(2010)矿评01-14-06)
国家自然科学基金项目(40972137)
关键词
地球化学
锆石U-PB定年
S型花岗岩
隆木岩体
加里东运动
华南陆内造山
赣州
江西
geochemistry
zircon U-Pb dating
S-type granite
Longmu Pluton
CaledonianMovement
intracontinental orogeny of South China
Ganzhou
J iangxi
