Low-temperature compatibility relations of the assemblage quartz-paragonite and the thermodynamic status of the phase rectorite
Low-temperature compatibility relations of the assemblage quartz-paragonite and the thermodynamic status of the phase rectorite
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石英-钠长石组合的低温相容关系与相累托石的热力学状态
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发表时间：
1973
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通讯作者：
N. Chatterjee
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作者：
N. Chatterjee
以天然低钠长石、高岭石和石英为原料，对钠基蒙脱石+2钠长石→钠长石+3钠长石+8石英反应进行了实验研究。在2kb、4kb和7 kb下的速率研究表明，从较低压力到较高压力，反应在335 - 315° C下发生。试图扭转这种反应持续几个月的运行是没有成功的。与天然矿物组合的有关数据比较表明，尽管不可逆，但本文所提供的数据可能非常接近石英-钠云母组合的真实热相容性下限，超过Na-蒙脱石相的压力稳定性上限，上述反应变为亚稳态;在这里，它被另一种反应1钠长石+1高岭石→ 1钠长石+2石英+1水所取代，正如Zen（1960）最初提出的那样。提供了显示石英-钠云母组合可能相容性关系的P-T网格（图4）。对属于Na 2 O-Al 2 O3-SiO2-H2O子系统的天然组合的研究为这种网格提供了证据。在本文报道的速率研究过程中，遇到了各种规则的钠蒙脱石-钠蒙脱石混层相（图2）; 1∶1规则混层相代表矿物累托石（有时称为钠蒙脱石）的合成类似物，广泛记录于深成岩和近变质环境。速率研究结果（图3）表明，混层相都是钠长石-钠基蒙脱石组合向钠长石-石英组合转化过程中的过渡亚稳产物。因此，累托石和相关的混合层相的连接蒙脱石-钠云母，总是不太稳定相对于组合钠蒙脱石-钠云母。
The reaction 3 Na-montmorillonite + 2 albite ⇌ 3 paragonite + 8 quartz has been studied experimentally using starting materials composed of natural low albite, kaolinite and quartz. Rate studies at 2, 4 and 7 kb demonstrate that the reaction takes place at ∼335−315° C from lower to higher pressures. Attempts to reverse this reaction with runs lasting several months were without success. Comparison with pertinent data from natural mineral assemblages indicate that despite non-reversal, the data presented here may be very near to the true lower thermal compatibility limit of the assemblage quartz-paragonite.The above reaction becomes metastable beyond the upper pressure stability limit of the phase Na-montmorillonite; it is replaced here by another reaction 1 albite + 1 kaolinite ⇌ 1 paragonite + 2 quartz + 1 H2O, as suggested originally by Zen (1960). A P-T-grid showing possible compatibility relations of the assemblage quartz-paragonite is provided (Fig. 4). Perusal of natural assemblages belonging to the subsystem Na2O-Al2O3-SiO2-H2O lends credence to this grid.In course of the rate studies reported here, various regular paragonite-sodium montmorillonite mixed-layer phases were encountered (Fig. 2); the 1∶1 regular mixed-layer phase represents the synthetic analogue of the mineral rectorite (sometimes called allevardite), widely recorded from deep diagenetic and anchimetamorphic environments. Results of rate-studies (Fig. 3) suggest that the mixed-layer phases are all transient, metastable products obtained during the transformation of the albite-Na-montmorillonite assemblage to paragonite-quartz. As such, rectorite and related mixed-layer phases on the join montmorillonite-paragonite, are always less stable relative to the assemblage Na-montmorillonite-paragonite.