豫南史庄一带金伯利岩中石榴子石矿物学特征及其形成条件的约束

豫南史庄一带位于华北地台南缘，分布有金伯利岩，为了确定岩石中的石榴子石矿物种类及其与金刚石的关系，通过人工重砂鉴定，对挑选出的40件石榴子石矿物单晶进行了电子探针微区化学成分分析。结果显示，区内石榴子石矿物族化学通式A3B2 [SiO4]3中的A组阳离子主要由Mg2+、Fe2+和少量Ca2+占位，B主组阳离子主要由Al3+和少量Fe3+、Cr3+、Mn3+占位，表明区内石榴子石主要为铁铝榴石(Alm)-镁铝榴石(Pry)-钙铝榴石(Gro)系列组合。根据矿物化学特征，区内镁铝榴石为榴辉岩型(E型)，具有含钛钙低铬富铁的特征，属Grutter等划分的G4-G5组(含钛、钙)镁铝-铁铝榴石，与金伯利岩、金刚石包体或者A组榴辉岩中的石榴子石特征相同。区内发现有超硅石榴子石，经计算其形成压力范围为10.2~10.9 GPa，对应深度超过250 km。

Mineralogical characteristics and constraints of formation conditions of garnet in kimberlite in Shizhuang area,southern He'nan Province

Shizhuang area in southern He nan located in the south margin of north China platform, with kimberlite.In order to determine the types of garnet and their relationship with diamond, 40 selected garnet mineral single crystals were analyzed by electron probe micro-area.The results show that the cations of group A in the general formula A3B2 [SiO4]3 of the garnet mineral group are mainly occupied by Mg2+, Fe2+ and a small amount of Ca2+, the cations of group B are mainly occupied by Al3+ and a small amount of Fe3+, Cr3+ and Mn3+.The garnet in the area is mainly composed of Alm - Pry - Gro series.According to the mineral chemical characteristics, the Mg-Al garnet in the area is eclogite type, which is characterized by titanium-calcium, low-chromium and iron-rich.It belongs to Grutter' s G4-G5 group(containing titanium and calcium)Mg-Al-Fe-Al garnet, and has the same characteristics as kimberlite, diamond inclusion or garnet in group A eclogite.Supersilicon garnet is found in the area, and its formation pressure ranges from 10.2 GPa to 10.9 GPa, with a depth of more than 250 km.