We have examined the suitability of a quartz-inclusions-in-epidote (qtz-in-ep) mineral barometer to better constrain P-T histories of epidote-bearing lithologies. Theoretical calculations applying an isotropic elastic model suggest that the qtz-in-ep barometer exhibits minimal temperature dependence, and thus, offers the potential to constrain growth conditions of epidote in various geologic environments, including skarn deposits, epidote-bearing granitoids, and metamorphic rocks. To test if the applied equations of state and isotropic elastic model reasonably simulate the elastic evolution of two anisotropic minerals, we measured Raman shifts of the 464 cm–1 band of quartz inclusions relative to that of an unencapsulated quartz standard. We calculated a quartz inclusion pressure (P464 incl) at various temperatures and compared these values with temperature-dependent Pincl predicted by elastic modeling (Pmod incl ) at elevated temperatures. Three epidote-bearing samples with reasonably well-constrained P-T histories were also examined: (1) sample HF14C from the Upper Schieferhuelle in the Western Tauern Window, Italy (P464 incl = 0.01 GPa); (2) sample LdC-31C from Lago di Cignana, Italy (P464 incl ≈ 0.16 GPa); and (3) sample FT1E from the Frosnitz Tal in the Western Tauern region, Austria (P464 incl = 0.57 GPa). Entrapment pressures (P464 ent ) calculated from P464 incl determined at various temperatures show nominal differences from Pent calculated from Pmod incl , suggesting that for qtz-in-ep pairs, the calculated Pent does not significantly vary with the temperature of measurement. Furthermore, our calculated P464 ent for a sample from the Upper Schieferhuelle is in agreement with petrographic context and previously established P conditions, and the P464 ent determined for the Frosnitz Tal sample closely approximate previously reported pressures. The Lago di Cignana sample is derived from an epidote vein that is encased in a high-P foliation, and the calculated P464 ent is consistent with early, low-P epidote vein formation that pre-dates high-P metamorphism, or alternatively, late vein formation during exhumation, and confirms that the epidote did not form at or near peak conditions (~2.0 GPa). The results of this study indicate that the qtz-in-ep barometer potentially provides another tool that geoscientists can employ to better constrain P-T conditions in some epidote-bearing environments, where conventional thermobarometric techniques cannot be applied.

中文翻译：

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石英包裹体绿帘石矿物气压计的评价与应用

我们研究了绿帘石中石英包裹体 (qtz-in-ep) 矿物气压计的适用性，以更好地限制含绿帘石岩性的 PT 历史。应用各向同性弹性模型的理论计算表明 qtz-in-ep 气压计表现出最小的温度依赖性，因此提供了限制绿帘石在各种地质环境中生长条件的潜力，包括矽卡岩沉积物、含绿帘石的花岗岩和变质岩. 为了测试应用的状态方程和各向同性弹性模型是否合理模拟了两种各向异性矿物的弹性演化，我们测量了 464 cm-1 石英包裹体带相对于未封装石英标准的拉曼位移。我们计算了不同温度下的石英包裹体压力 (P464 incl)，并将这些值与通过弹性模型 (Pmod incl ) 在升高的温度下预测的温度相关 Pincl 进行了比较。还检查了三个具有合理约束 PT 历史的带有绿帘石的样品：（1）来自意大利西陶恩窗（Western Tauern Window）的 Upper Schieferhuelle 的 HF14C 样品（P464 包括 = 0.01 GPa）；(2) 来自意大利 Lago di Cignana 的 LdC-31C 样品 (P464 incl ≈ 0.16 GPa)；(3) 来自奥地利西陶恩地区 Frosnitz Tal 的 FT1E 样本（P464 包括 = 0.57 GPa）。在不同温度下根据 P464 incl 计算的截留压力 (P464 ent ) 显示出与根据 Pmod incl 计算的 Pent 的名义差异，表明对于 qtz-in-ep 对，计算出的 Pent 不会随测量温度发生显着变化。此外，我们为来自上 Schieferhuelle 的样品计算的 P464 ent 与岩相背景和先前建立的 P 条件一致，并且为 Frosnitz Tal 样品确定的 P464 ent 与先前报告的压力非常接近。Lago di Cignana 样本来自被高磷叶理包裹的绿帘石脉，计算出的 P464 ent 与早于高磷变质作用或晚期的早期低磷绿帘石脉形成一致挖掘过程中静脉形成，并证实绿帘石没有在或接近峰值条件 (~2.0 GPa) 形成。