东南极拉斯曼丘陵柱晶紫苏堇青麻粒岩中堇青石的矿物学特征  

Mineralogical Characteristics of Cordierites in Krn Hy Crd Granulites from the Larsemann Hills, East Antarctica

作　　者：仝来喜[1] 张振禹[1] 刘小汉[1] 韩秀伶[1] 刘蔚玲[1] 

机构地区：[1]中国科学院地质研究所

出　　处：《岩石学报》1997年第3期395-405,共11页Acta Petrologica Sinica

基　　金：国家"八五"攻关;中国科学院"八五"重大基础项目

摘　　要：东南极拉斯曼丘陵晚元古代（１０００Ｍａ）高级变质杂岩中区域性产出一套粗粒柱晶紫苏堇青麻粒岩，其原岩为含硼的富镁铝泥质岩。岩石中结晶粗大的堇青石在矿物化学成分上属于镁堇青石，其成分显示不均匀且具较明显成分环带的特征，从核部到边缘，其ＸＭｇ（Ｍｇ／Ｍｇ＋Ｆｅ２＋）比值由０．８５５变化为０．８１６。温压计算结果表明，所研究堇青石形成的Ｐ－Ｔ条件约为０．７６～０．７２ＧＰａ和８６０℃～８３０℃（核部至边缘）。Ｘ－射线粉晶结构分析证明这种堇青石属于低位结构状态的堇青石，晶体结构扭曲指数Δ＝０．２８～０．３０，在自然界比较少见。实验室合成的低位结构状态的堇青石只在持续较长时间的１３００℃～１４００℃的高温条件下稳定存在。因此，这意味着低位堇青石可能是由很高温变质作用及缓慢冷却的条件下结晶形成，这对于研究该区的地壳演化具有极其重要的意义。A series of coarse grained kornerupine hyperthene cordierite granulites occur as layers in the late Proterozoic(1000Ma) high grade metamorphic complex outcropping in the Larsemann Hills, East Antarctica.Their protoliths are boron bearing magnesium rich aluminous pelites. These coarsely recrystallized cordierite megacrystals in the granulites belong to Mg cordierites in composition, whose compositions show the characteristics of heterogeneity and obvious zoning in composition.From the core to the rim, their X Mg (Mg/Mg+Fe 2+ ) values vary from 0 855 to 0 816.The P T conditions of the formation of the studied cordierites have been estimated as 0 76￣0 72GPa and 860℃￣830℃(from core to rim).The X ray structural analysis for cordierites confirmed that the cordierites belong to low structure state cordierites, in which their distortion index Δ=0 28￣0 30, uncommon in the natural world.The cordierites synthesized in laboratory are only stable under the P T conditions of long lasting high temperature (1300℃￣1400℃). Therefore, it implies that the megacrystal cordierites were formed by very high temperature metamorphism under slow cooling conditions.This study is of important implications for crustal evolution of the region.

关 键 词：麻粒岩 堇青石 矿物学 紫苏堇青麻粒岩 

分 类 号：P588.346[天文地球—岩石学] P588.36[天文地球—地质学]