【作者】 张敏； 袁忠信；

【Author】 Zhang Min (Department of Geology,Zhongshan University) Yuan Zhongxing (Institute of Mineral Deposits,Chinese Academy of Geological Sciences)

【机构】 中山大学地质系； 矿床地质研究所；

【摘要】 文章对“八○一”稀有元素碱性花岗岩的两个岩体及围岩进行了全岩、石英, 钾长石的氧同位素分析,以及东岩体全岩的锶同位素分析。东岩体的δ¹⁸O_全岩为-5．61—+ 2．87‰,平均-2．67‰；(⁸⁷Sr/⁸⁶Sr)_i 值为0．7071；δ¹⁸O_石英为+4．16—+6．00‰,δ¹⁸O_钾长石 为-4．81—-10．42‰；△¹⁸O_{石英-钾长石}为+10．40-+14．58‰。西岩体的δ¹⁸O_全岩为-2．10‰, δ¹⁸O_石英为+0．98-+5．09‰,δ¹⁸O_钾长石为-7．89‰,△¹⁸O_{石英-钾长石}为+12．987‰。围岩火山岩的δ¹⁸O_全岩为-7．18-+1．37‰。碱性花岗岩为明显贫化¹⁸O 的花岗岩。根据上列数据与岩体地质特征,花岗岩的低¹⁸O 特征,可能是由地下水与侵入体间的同位素交换引起的；形成岩体的岩浆是上地幔岩浆分异的产物。这种岩浆侵入地壳表部加热了地下水,正是这种地下水热液,一方面与已结晶的岩体发生氧同位素交换,使岩石成为低¹⁸O 花岗岩,另一方面向深部对流循环,将稀有,稀土元素带至岩体上部,促其在上部蚀变带中富集．更多还原

【Abstract】 O isotopic analysis of two intrusive bodies and wall rocks （whole rock, potash feldspar） and Sr isotopic analysis of the eastern rock body （whole rock） were recpectively carried out for the“801”RE alkali granite with the results as follows:for the eastern rock body δ¹⁸O whole rock=-5.61- +2.8‰,averaging-2.67‰.⁸⁷Sr/⁸⁵Sri=0.7071,δ¹⁸O_quartz=+4.16-+6.00‰, δ¹⁸O_k-feldspar=-4.81--10.42‰。and δ¹⁸O_Q-KF=10.40-14.58‰.For the west- ern rock body,δ¹⁸O_{whole rock}=-2.1‰,δ¹⁸O_quartz=+0.98-+5.09‰, δ¹⁸O_K-feldspar=-7.89‰,and ⊿δ¹⁸O_Q-KF=12.98‰.For the volcanic wall rocks, δ¹⁸O_{whole rock}=-7.18-+1.37‰.The alkali granite is obviously depleted in ¹⁸O. In the light of the data and geological characters mentioned above,it is concluded that the low ¹⁸O property of the granite might have resulted from the isotopic exchanges between underground water and the intrusive body which was formed by differentiation of mantle magma intruding the upper Crust and warming up the underground water that on one hand exchanged its O isotope with the crystallized rock body and made the rock become a gran- ite with low ¹⁸O value and on the other hand circulated towards,the depth, carrying the REE to the upper part of the rock body and causing these elements to be concentrated at the upper alteration zone.更多还原