P-T grids for silica-undersaturated granulites in the systems MAS (n+ 4) and FMAS (n+ 3)-tools for the derivation of P-T paths of metamorphism
P-T grids for silica-undersaturated granulites in the systems MAS (n+ 4) and FMAS (n+ 3)-tools for the derivation of P-T paths of metamorphism
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MAS (n 4) 和 FMAS (n 3) 系统中二氧化硅不饱和麻粒岩的 P-T 网格 - 用于推导变质作用 P-T 路径的工具
DOI：
10.1111/j.1525-1314.1987.tb00383.x
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发表时间：
1987
影响因子：
3.4
通讯作者：
B. Hensen
中科院分区：
文献类型：
--
作者：
B. Hensen
摘要考虑FeO-MgO-Al2O3-SiO2 （FMAS）体系中含有堇青石（Cd）、蓝宝石（Sa）、高岭石（Hy）、石榴石（Ga）、尖晶石（Sp）、硅线石（Si）和刚玉（Co）等矿物，其稳定不变量点为[Co]、[Ga]、[Cd]和[Sa]。实验数据的约束表明，在低ph20条件下，不变量点出现在高温（900℃）和中压（7-10 kbar）。这一温度高于通常认为的麻粒岩相变质温度。在麻粒岩中，铁-镁交换地温计可以得到低于变质峰条件100-150℃的温度，残余的高温组合和正辉石中富al岩心最能保存峰值温度的证据。将FMAS网格应用于一些记录良好的麻粒岩产状，对它们的P-T历史产生了重要的限制。不同体积组成的岩石，在野外近距离出现，可能记录其P-T路径的不同片段。这尤其适用于具有日冕、复体和分带矿物形式的反应证据的岩石。考虑弯曲的反应边界和XMs等层可以解释低温实验和热化学计算与高温实验数据对堇青石稳定性的明显矛盾的结果。
Abstract Considering the minerals cordierite (Cd), sapphirine (Sa), hypersthene (Hy), garnet (Ga), spinel (Sp), sillimanite (Si) and corundum (Co) in the system FeO-MgO-Al2O3-SiO2 (FMAS), the stable invariant points are [Co], [Ga], [Cd] and [Sa]. Constraints imposed by experimental data for the system MAS indicate that under low PH2o conditions the invariant points occur at high temperature (> 900° C) and intermediate pressure (7-10 kbar). This temperature is higher than that commonly advocated for granulite facies metamorphism. In granulites Fe-Mg exchange geothermometers may yield temperatures of 100–150° C below peak metamorphic conditions and evidence for peak temperatures is best preserved by relict high-temperature assemblages and by Al-rich cores in orthopyroxene. Application of the FMAS grid to some well-documented granulite occurrences introduces important constraints on their P-T histories. Rocks of different bulk compositions, occurring in close proximity in the field, may record distinct segments of their P-T paths. This applies particularly to rocks with evidence for reaction in the form of coronas, symplectites and zoned minerals. Consideration of curved reaction boundaries and XMs isopleths may explain apparently contradictory results for the stability of cordierite obtained from low-temperature experiments and thermochemical calculations on the one hand and hightemperature experimental data on the other.