Silica mineral is present in different stable polymorphs depending on the temperature and pressure conditions of crystallization. We suggest using silica mineral phases to constrain the thermal history of eucrites. We focused on silica minerals in basaltic clasts of nine non-cumulate eucrites to compare with previously studied cumulate eucrites. Our observations indicate an apparent relationship between thermal metamorphic degrees and silica phase texture in basaltic clasts of non-cumulate eucrites. To reveal complex transformation relations between silica polymorphs in eucrites, we performed cooling experiments (cooling rate: 1 and 0.1 °C h⁻¹) and heating experiments (heating 500 °C for 168 h and 800 °C for 96 h) using eucrites. The cooling experiments show that cristobalite is an initial silica phase crystallized from eucritic magma and transforms to quartz at the cooling rate between 0.1 and 1 °C h⁻¹. Based on the cooling experiments and observations of eucrites, we suggest that a combination of silica minerals varies depending mainly on cooling rates. According to the heating experiments, monoclinic tridymite hardly transforms to other phases at low temperature by short reheating events such as brecciation. Monoclinic tridymite can partially transform to quartz with a “hackle” fracture. We conclude that a reheating event partially transformed monoclinic tridymite to quartz to form aggregates of monoclinic tridymite and quartz with the hackle fracture in eucrites. We suggested that some basaltic clasts in non-cumulate eucrites experienced two-stage thermal metamorphism in the eucritic crust. The first metamorphic event has resulted from burial under lava produced by successive eruptions. Igneous intrusions into the preformed crust may have caused the second metamorphic event. The intrusions heated the deep eucritic crust and induced the transformation from monoclinic tridymite to quartz.

中文翻译：

---

二氧化硅相的关联作为真晶质地温气压计：对真晶质地壳中两阶段热变质作用的影响

二氧化硅矿物根据结晶的温度和压力条件以不同的稳定多晶型物存在。我们建议使用二氧化硅矿物相来限制晶体的热历史。我们专注于九个非累积晶析晶的玄武岩碎屑中的二氧化硅矿物，以与先前研究的累积晶析晶进行比较。我们的观察表明，非累积晶析岩玄武岩碎屑中的热变质程度与二氧化硅相结构之间存在明显的关系。为了揭示晶体中二氧化硅多晶型物之间复杂的转化关系，我们进行了冷却实验（冷却速率：1 和 0.1 °C h ^-1) 和加热实验 (加热 500 °C 168 小时和 800 °C 96 小时) 使用 eurites。冷却实验表明方石英是从晶质岩浆结晶的初始二氧化硅相，并以 0.1 至 1 °C h ^-1的冷却速率转变为石英. 根据冷却实验和对晶体的观察，我们认为二氧化硅矿物的组合主要取决于冷却速度。根据加热实验，单斜鳞石英在低温下很难通过角砾化等短暂的再加热事件转变为其他相。单斜鳞石英可以部分转变为石英，并带有“裂纹”裂缝。我们得出结论，再加热事件部分地将单斜鳞屑岩转化为石英，形成单斜鳞屑岩和石英的聚集体，并在 Eucrite 中出现裂纹。我们认为，非累积晶壳中的一些玄武质碎屑在晶壳中经历了两阶段热变质作用。第一次变质事件是由连续喷发产生的熔岩掩埋引起的。火成岩侵入预先形成的地壳可能导致了第二次变质事件。侵入体加热了深层的真晶质地壳并诱导了单斜鳞石英向石英的转变。