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首页> 外文期刊>Contributions to Mineralogy and Petrology >Chlorite stability in mantle peridotite: the reaction clinochlore + enstatite = forsterite + pyrope + H_2O
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Chlorite stability in mantle peridotite: the reaction clinochlore + enstatite = forsterite + pyrope + H_2O

机译：地幔橄榄岩中亚氯酸盐的稳定性：斜绿石+顽辉石=镁橄榄石+吡啶+ H_2O

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摘要

Chlorite crystallising in hydrated mantle peridotite is a potential source of water for subduction zone volcanism. The reaction clinochlore + enstatite = forsterite + pyrope + H_2O is the important reaction for defining the stability of chlorite in these rocks. It has been investigated in phase-equilibrium experiments in piston-cylinder and multi-anvil apparatus between 2 and 5 GPa. The reaction has a steep, negative P-T slope at low pressures, with brackets at 860-880 deg C at 2.5 GPa, 840-860 deg C at 3.0 GPa, and 820-840 deg C at 3.5 GPa. The reaction flattens out with increasing pressure to approx 5.0 GPa at 650 deg C. Chlorite compositions close to the reaction were determined from unit-cell parameters measured using high-resolution synchrotron powder diffraction. These showed a decrease in Al content with increasing pressure along the reaction, consistent with calculations using a previously published thermodynamic data set. The experimental results are consistent with the results of earlier studies on the reaction defining the maximum thermal stability of clinochlore, clinochlore = forsterite + pyrope + spinel + H_2O. They have been used in the derivation of revised thermodynamic data for clinochlore in the latest version of the previously published data set. The new results show that chlorite in subducting slab or overlying mantle wedge could dehydrate below subduction zone volcanoes and be a major source of the water required for melting. However, the dehydration reaction is not sufficiently pressure-dependent to be responsible for the narrow range in depth from the volcanoes to the slab, and chlorite will not be the only hydrous mineral involved.
机译：水合地幔橄榄岩中的亚氯酸盐结晶是俯冲带火山作用的潜在水源。斜绿石+顽石=镁橄榄石+吡啶+ H_2O是确定这些岩石中亚氯酸盐稳定性的重要反应。已经在2到5 GPa之间的活塞缸和多砧装置的相平衡实验中对此进行了研究。该反应在低压下具有陡峭的负P-T斜率，在2.5 GPa时于860-880摄氏度，在3.0 GPa时于840-860摄氏度，在3.5 GPa时于820-840摄氏度的托槽。在650℃下，随着压力增加到约5.0GPa，反应变平。接近反应的亚氯酸盐组成由使用高分辨率同步加速器粉末衍射测量的晶胞参数确定。这些结果表明，随着反应压力的增加，Al含量降低，这与使用先前发布的热力学数据集进行的计算一致。实验结果与较早的研究结果一致，该反应定义了斜绿石的最大热稳定性，斜绿石=镁橄榄石+吡啶+尖晶石+ H_2O。在先前发布的数据集的最新版本中，已将它们用于推导的氯氰菊酯的修订热力学数据。新的结果表明，俯冲板块或上覆地幔楔中的绿泥石可能在俯冲带火山口下方脱水，并且是融化所需水的主要来源。然而，脱水反应的压力依赖性不足，不足以造成从火山到板块的深度范围狭窄，绿泥石将不是唯一的含水矿物。

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