大龙山岩体冷却史及其成矿关系的同位素研究  

AN ISOTOPE STUDY ON THE COOLING HISTORY OF THEDALONGSHAN GRANITIC MASSIF AND ITS BEARINGON MINERALIZING PROCESS

作　　者：郑永飞[1,2,3] 魏春生[1,2,3] 王峥嵘[1,2,3] 黄耀生[1,2,3] 张宏 

机构地区：[1]中国科学技术大学地球和空间科学系 [2]南京大学地球科学系 [3]北京铀矿地质研究院

出　　处：《地质科学》1997年第4期465-477,共13页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：国家自然科学基金;中国科学院专项基金

摘　　要：根据全岩Ｒｂ－Ｓｒ、锆石Ｕ－Ｐｂ和角闪石、黑云母、钾长石Ｋ－Ａｒ同位素年龄综合测定结果，再造了安庐石英正长岩带中大龙山岩体的冷却史。矿物对氧同位素地质测温结果证实，扩散作用是控制同位素体系封闭的主导因素。假定岩体冷却与地温梯度（１００℃／Ｍａ）同步降低，以二维热模式为参照，可以推算出大龙山岩体的原始侵位深度约为８ｋｍ，成岩温度为８００±５０℃。早阶段石英正长岩体在１３６Ｍａ侵位结晶后开始快速的冷却上升，冷却速率为２７．４℃／Ｍａ，上升速率为０．２７ｍｍ／ａ；经过约１８Ｍａ后，岩体上升至地下约３ｋｍ深处，温度为３００±５０℃，转为缓慢冷却上升，冷却速率为６．３℃／Ｍａ，上升速率为０．０６ｍｍ／ａ。晚阶段碱长花岗岩体于１１７Ｍａ侵位结晶，嗣后开始快速的冷却上升，冷却速率为５８．６℃／Ｍａ，上升速率为０．５９ｍｍ／ａ；经过约８Ｍａ后，岩体转为缓慢冷却上升，冷却速率为７．２℃／Ｍａ，上升速率为０．０７ｍｍ／ａ。结合对国内外其它深成岩体冷却历史的研究，可见这类岩体的侵位上升一般经历了两个阶段：（１）早期高温岩体快速上升至定位，冷却速率显著大于区域地温梯度降低幅度；（２）晚期低温岩体与区域地质体一起缓慢隆起上升，冷却速?geothermometry of mineral-pairs demonstrates that diffusion is a predominant factor to control the closure of isotopic systems. According to the theory of cooling ages, it is reckoned that the Dalongshan massif would have at first experienced a rapidly cooling process since its crystallization and then become slow. The early phase of quartz syenite in the musif was emplaced in 1 36Ma at 800 ± 50℃ and become cold rapidly to sometime in 118Ma at 300± 50℃, with a cooling rate of 27.4℃ / Ma. Afterwards it would have experienced a slowly cooling process up to 94 Ma at 1 50 ± 30℃ , with a cooling rate of 6.3℃ / Ma. The late phase of alkaline granite would have experienced a rapidly cooling from 1 1 7 Ma to 1 09Ma with a cooling rate of 5 Abstrsct **Whole-rock Rb-Sr, zircon U-Pb as well as hornblende, biotite and K-feldspar K-Ar isotopic ages are used to reconstruct the. themal history of the Dalongshan granite massif on the An-Lu quartz syenite belt in Anhui. Oxygen isotope8.6℃ / Ma. Then it becomes slow with a cooling rate of 7.2℃ / Ma, which is similar to that for the early phase of quartz syenite. Assuming that the cooling of the massif is determined by local geothermal gradients, an emplacement depth of about 8km is inferred if the local geothermal gradient would be 1 00℃ / km. In this respect the Dalongshan massif was uplifted rapidly in 0.27 to 0.59mm / a at the first stage but slowly in 0.06 to 0.07mm/ a at the second stage. A certain hydrothermal uranium deposit was found to be located in the contact zone of the Dalongshan massif with wall-rock sandstone. The time and temperature of the uranium mineralization are identical to the closure of argon diffusion in biotite, suggesting a genetic correlation between the massif cooling history and the uranium mineralizing process.

关 键 词：花岗岩 同位素年龄 氧同位素 冷却历史 矿化作用 

分 类 号：P619.222[天文地球—矿床学] P588.121[天文地球—地质学]