Sapphirine parageneses from the Caraiba complex, Bahia, Brazil: the influence of Fe2+–Fe3+ distribution on the stability of sapphirine in natural assemblages
Sapphirine parageneses from the Caraiba complex, Bahia, Brazil: the influence of Fe2+–Fe3+ distribution on the stability of sapphirine in natural assemblages
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来自巴西巴伊亚 Caraiba 杂岩的蓝宝石共生体：Fe2+–Fe3+ 分布对天然组合中蓝宝石稳定性的影响
DOI：
10.1111/j.1525-1314.1987.tb00388.x
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发表时间：
1987
影响因子：
3.4
通讯作者：
B. Windley
中科院分区：
文献类型：
--
作者：
D. Ackermand;R. Herd;M. Reinhardt;B. Windley
含蓝宝石的岩石赋存于巴西太古宙Caraiba杂岩库拉卡河谷侵入的石英长石质正片麻岩中的三个可整合的米级透镜中。在透镜中有六种不同的含蓝宝石的岩石类型，它们具有以下相(每一种都另外含有金云母)：
A：蓝宝石、斜方辉石；
B：蓝宝石、堇青石、斜方辉石、尖晶石；
C：蓝宝石、堇青石；
D：蓝宝石、堇青石、斜方辉石、石英；
E：蓝宝石、堇青石、斜方辉石、硅线石、石英；
F：蓝宝石、堇青石、钾长石、石英。
然而，接触中既没有蓝宝石和石英，也没有斜辉石和硅线石。在糜棱岩化过程中，三种不含石英的岩石(代表残留原岩物质)中引入了二氧化硅，形成了三种含堇青石和石英的岩石。较多镁质岩石中的稳定共生矿物为蓝宝石-斜方辉石和蓝宝石-堇青石。在富铁较多的岩石中，稳定的有蓝宝石-堇青石、蓝宝石-堇青石-硅线石、堇青石-硅线石、蓝宝石-堇青石-尖晶石-磁铁矿和石英-堇青石-斜方辉石。六种岩石中蓝宝石中的氧化铁含量按C、F-A、D-B、E的顺序依次增加，从平均2.0wt%增加到10.5wt%(以FeO计)。
与蓝宝石透镜有关的四种岩石类型是：
I：斜方辉石、堇青石、黑云母、石英、长石英云闪长岩-花岗闪长片麻岩；
II：黑云母、石英、长石片麻岩；
III：斜方辉石、单斜辉石、角闪石、斜长偏钠辉石；
IV：黑云母、斜方辉石、石英、长石、石榴石、堇青石、硅线石、麻粒片麻岩。
IV型稳定伴生矿物为斜方辉石-堇青石-石英、石榴石-硅线石-石英和石榴石-堇青石-硅线石。
地质温压测量表明，伴生主岩在720-750℃和5.5-6.5kbar之间达到平衡。FMASH和FMAFSH(FeO-MgO-Al_2O_3-Fe_2O_3-SiO_2-H_2O)模型体系的岩石成因网格表明，在这些P-T条件下，不含石榴石的蓝宝石组合受到高Fe3+含量和高XMG=(mg/(Mg+Fe2+))的稳定。
Sapphirine-bearing rocks occur in three conformable, metre-size lenses in intrusive quartzo-feldspathic orthogneisses in the Curaca valley of the Archaean Caraiba complex of Brazil. In the lenses there are six different sapphirine-bearing rock types, which have the following phases (each containing phlogopite in addition):
A: Sapphirine, orthopyroxene;
B: Sapphirine, cordierite, orthopyroxene, spinel;
C: Sapphirine, cordierite;
D: Sapphirine, cordierite, orthopyroxene, quartz;
E: Sapphirine, cordierite, orthopyroxene, sillimanite, quartz;
F: Sapphirine, cordierite, K-feldspar, quartz.
Neither sapphirine and quartz nor orthopyroxene and sillimanite have been found in contact, however. During mylonitization, introduction of silica into the three quartz-free rocks (which represent relict protolith material) gave rise to the three cordierite and quartz-bearing rocks. Stable parageneses in the more magnesian rocks were sapphirine–orthopyroxene and sapphirine–cordierite. In more iron-rich rocks, sapphirine–cordierite, sapphirine-cordierite–sillimanite, cordierite–sillimanite, sapphirine–cordierite–spinel–magnetite and quartz–cordierite–orthopyroxene were stable. The iron oxide content in sapphirine of the six rocks increases from an average of 2.0 to 10.5 wt % (total Fe as FeO) in the order: C,F–A,D–B,E. With increase in Fe there is an increase in recalculated Fe2O3 in sapphirine.
The four rock types associated with the sapphirine-bearing lenses are:
I: Orthopyroxene, cordierite, biotite, quartz, feldspar tonalitic to grandioritic gneiss;
II: Biotite, quartz, feldspar gneiss;
III: Orthopyroxene, clinopyroxene, hornblende, plagioclase meta-norite;
IV: Biotite, orthopyroxene, quartz, feldspar, garnet, cordierite, sillimanite granulite gneiss.
The stable parageneses in type IV are orthopyroxene–cordierite–quartz, garnet–sillimanite–quartz and garnet–cordierite–sillimanite.
Geothermobarometry suggests that the associated host rocks equilibrated at 720–750°C and 5.5–6.5 kbar. Petrogenetic grids for the FMASH and FMAFSH (FeO–MgO–Al2O3–Fe2O3–SiO2–H2O) model systems indicate that sapphirine-bearing assemblages without garnet were stabilized by a high Fe3+ content and a high XMg= (Mg/ (Mg+Fe2+)) under these P–T conditions.