大别山南部蛇纹岩碳硅石研究

在大别山南部亭子岭、古山、虎形等蛇纹岩中发现碳硅石，粒径0.02~0.08mm，少数可达0.1~0.17mm，晶体有一轴晶（+）和二轴晶（+）（2V=37°），后者较发育，有较明显的二轴晶化。拉幔光谱峰值稳定，主峰788~789cm-1次峰968~972cm-1，弱峰767~784cm-1，个别样品产生较大偏移，主峰776.85cm-1，次峰964.82cm-1，可能为因其他微量元素的加入，结构发生改变所致。能谱分析显示，碳硅石混入较多杂质，其中最明显的O、Fe、Ca、K、Ni、Ti、S、Cl、Na等元素可能对结构产生一定的影响。从而也揭示了早期结晶的温度较高，杂质也较多。此外，碳硅石中见有流体包裹体，成分为CH4、C2H6、C3H8、C6H6、H2O等，产生碳硅石的蛇纹岩为大陆幔源岩石在上侵过程中，高温下差异性应变形成二轴晶化。根据实验资料，SiC形成温度为1600℃以上，压力大于等于6.0Gpa，应为在下地壳上地幔软流圈极端还原条件下产生的。

A study of moissanites in the serpentinite from south Dabie Mountain

Moissanites were found in serpentinites from Tinziling, Gushan and Huxi areas in south Dabie Mountain. The sizes of grains are mainly 0.02~0.08mm and subordinately 0.1~0.17mm. The crystals are uniaxial (+) and biaxial (+), 2V=370° with the biaxial crystals being dominant, showing obvious biaxiality.The Raman shifts of moissanites in the section are stable:a primary peak of 788~789cm-1, a secondary peak of 986~972cm-1, and a weak peak of 767~784cm-1. The mixture of Al, O in moissanites may cause change in texture of moissanites, and even cause comparatively larger deviation in Raman spectral analysis: a primary peak of 776.85cm-1, and a secondary peak of 964.82cm-1. The energy spectral analysis shows that the moissanites were mixed with a lot of other elements, such as O, Fe, Ca, K, Ni, Ti, S, Cl and Na. All of these elements may affect its texture. It is also shown that at the early stage it crystallized at relatively high temperature and had relatively abundant mixed elements. Besides, there exist fluid inclusions in moissanates, whose components include CH4, C2H6, C3H8, C6H6, H2O, etc. The moissanite-bearing serpentinite is a continent mantle rock; when it intruded upward, the biaxial crystal of moissanite was formed under the condition of high temperature and different stresses. According to experimental data, SiC was formed at the temperature >1600℃ and under the pressure≥6.0GPa. Therefore the moissanites here should have been produced under extremely low reduction condition, situated in asthenosphere of the upper mantle or the lower earth crust.