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首页> 外文期刊>Contributions to Mineralogy and Petrology >Significance of 'stretched' mineral inclusions for reconstructing P-T exhumation history
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Significance of 'stretched' mineral inclusions for reconstructing P-T exhumation history

机译：“拉伸”矿物包裹体对重建P-T掘尸史的意义

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摘要

Analysis of mineral inclusions in chemically and physically resistant hosts has proven to be valuable for reconstructing the P-T exhumation history of high-grade metamorphic rocks. The occurrence of cristobalite-bearing inclusions in garnets from Gore Mountain, New York, is unexpected because the peak metamorphic conditions reached are well removed (>600 degrees C too cold) from the stability field of this low-density silica polymorph that typically forms in high temperature volcanic environments. A previous study of samples from this area interpreted polymineralic inclusions consisting of cristobalite, albite and ilmenite as representing crystallized droplets of melt generated during a garnet-in reaction, followed by water loss from the inclusion to explain the reduction in inclusion pressure that drove the transformation of quartz to cristobalite. However, the recent discovery of monomineralic inclusions of cristobalite from the nearby Hooper Mine cannot be explained by this process. For these inclusions, we propose that the volume response to pressure and temperature changes during exhumation to Earth's surface resulted in large tensile stresses within the silica phase that would be sufficient to cause transformation to the low-density (low-pressure) form. Elastic modeling of other common inclusion-host systems suggests that this quartz-to-cristobalite example may not be a unique case. The aluminosilicate polymorph kyanite also has the capacity to retain tensile stresses if exhumed to Earth's surface after being trapped as an inclusion in plagioclase at P-T conditions within the kyanite stability field, with the stresses developed during exhumation sufficient to produce a transformation to andalusite. These results highlight the elastic environment that may arise during exhumation and provide a potential explanation of observed inclusions whose stability fields are well removed from P-T paths followed during exhumation.
机译：事实证明，对具有化学和物理抗性的宿主中的矿物包裹体进行分析对于重建高级变质岩的P-T掘出历史非常有价值。来自纽约戈尔山的石榴石中含有方石英的夹杂物的出现是出乎意料的，因为从这种低密度二氧化硅多晶型物的稳定场中可以很好地消除达到的峰值变质条件（> 600°C，太冷）。高温火山环境。先前对该区域样品的研究认为，由方石英，钠长石和钛铁矿组成的多矿物夹杂物代表石榴石加入反应过程中生成的结晶熔体液滴，随后水分从夹杂物中流失，以解释推动转化的夹杂物压力降低石英到方石英。然而，这一过程无法解释最近从附近的胡珀矿发现的方石英单矿物包裹体的原因。对于这些夹杂物，我们建议在掘出到地球表面期间对压力和温度变化的体积响应会导致二氧化硅相内部产生较大的拉应力，这足以引起向低密度（低压）形式的转变。其他常见的夹杂物-主体系统的弹性建模表明，这种石英-方石英的例子可能不是唯一的情况。铝硅酸盐多晶型蓝晶石还具有在蓝晶石稳定性场内P-T条件下被夹杂在斜长石中夹杂在斜长石中后被掘出到地球表面时保持拉伸应力的能力，在挖掘过程中产生的应力足以产生转变为红柱石。这些结果突出了在掘尸过程中可能出现的弹性环境，并为观察到的夹杂物提供了潜在的解释，其包裹体在掘尸过程中从P-T路径中被很好地去除了。

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