四川盐边基性-超基性杂岩体中角闪石矿物学研究

A MINERALOGICAL STUDY OF HORNBLENDES FROM THE BASIC-ULTRABASIC COMPLEXES IN YANBIAN,SICHUAN PROVINCE

本文采用光学法、探针分析法、红外光谱法、单晶X射线衍射法对杂岩体中角闪石进行了详细的研究,总结了各期岩体中角闪石的特征。从早期到晚期,角闪石光性呈递变关系,2V由(-)76.7→(+)84.2;化学成分呈规律性变化,Si、Fe含量减少,Al、Mg、Na含量增加,矿物种属明显地呈浅闪石质角闪石→含铁韭闪石→韭闪石的变化规律,因而首次在该区确定了含铁韭闪石、韭闪石矿物的存在;红外光谱随T类阳离子Al^(Ⅳ)/Si值,C类阳离子Fe/Mg值呈规律性变化;晶胞参数也显示规律性变化,a由9.838—9.866A,b由18.047—17.980A,c由5.308—5.295A,V由910.73—906.55A^3。清楚地反映了该区角闪石各期演化上的“血缘”关系和差异。同时,探讨了各期角闪石的结晶温度(770—1114℃);成因类型为基性及超基性岩浆型,岩浆来源于上地幔;超基性岩具有地幔交代成因特征。

In this paper the results of detailed studies of a widely present mineral-hornblende from the complexes are presented, using optical analysis, electronmicroprobe analysis, infrared spectrometry and single-crystal X-ray diffraction.The characteristics of hornblendes from the rocks formed at different stagesare summarized. From early to late, the optical nature of the hornblendeschanges successively: 2V from (-) 76.7 to (+) 84.2; their chemical composi-tion varies regularly; Si and Fe contents decrease but Al, Mg and Na contentsincrease. The existence of ferri-ferous pargasite and pargasite in this area hasbeen confirmed for the first time. Infrared spectra vary regularly with theratio of Al~Ⅳ/Si for T type and with that of Fe/Mg for C type. Unit cellparameters also display regular variatons: a, 9. 838-9. 866 A' b, 18. 047-17. 980 A;c, 5. 308-5. 295 A; β, 104. 91-105. 18°. V, 910. 73-906. 55 A^3. These make clear the 'consanguinity' relationship and differences between the hornblendes from therocks of different stages in this area. At the same time, their crystallizationtemperatures (770-1114℃) are also discussed. The present study shows thatthe hornblendes are of basic and ultrabasic magmatic origin. The magma camefrom the upper mantle and the ultrabasic rocks are of mantle replacement origin.