Eucirtes are the most common HED meteorites. Their prominent characteristics are the widespread development of thermal metamorphism. Pyroxene is the main mineral composition of this type of meteorite. This mineral is most affected by thermal metamorphism, so the mechanism of thermal metamorphism is a research focus. This paper analyzes the petrological characteristics and the mineral composition of pyroxenes of a group of eucirtes by BSE images and EPMA method. Based on the characteristics of petrology,thermal metamorphism and composition of pyroxenes,these meteorites with structures of coarse crystal accumulated gabbro,ophitic and basaltic textures from gabbro,diabase and basalt respectively,the width of the melt belts,the complexity of melt combination,the diameter of recrystallized particles are increasing,while the depth of crystallization from deep to shallow. The compositions of pyroxenes change from hypersthene (Fs34. 1 - 62. 9Wo1. 83 - 4. 96) to pigeonite(Fs44. 1 - 65. 3Wo5. 11 - 22. 3) and augite (Fs14. 2 - 47. 7Wo25. 0 - 45. 0) . These evidences prove that the heat source came from upper covering layer,not from lower rocks. The analysis above shows that the cause of this common metamorphism may result from rapid burial of early basalts by later flows caused by high effusion rates on the mother body.%采用背散射电子图像和电子探针矿物成分分析相结合的方法, 研究了 3 块钙长辉长无球粒陨石样品.通过岩石学特征、热变质特征和辉石的矿物化学成分分析发现, 3 块陨石分别呈粗晶辉长堆晶结构、辉绿结构和玄武岩质结构, 从辉长岩→辉绿岩→玄武岩, 出熔条带宽度增加, 出熔组合复杂度增加, 重结晶颗粒增大, 而形成深度则由深变浅, 辉石成分从以紫苏辉石(Fs34. 1 ～ 62. 9 Wo1. 83 ～ 4. 96) 为主, 过渡到以易变辉石(Fs44. 1 ～ 65. 3Wo5. 11 ～ 22. 3) 和普通辉石(Fs14. 2 ～ 47. 7Wo25. 0 ～ 45. 0) 为主.这些证据说明热变质的热量来源于上部而不是内部, 这类陨石的热变质主要是由于母体中玄武岩浆喷发覆盖加热所造成的.
展开▼
