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The versatility of petrological modeling: Thermobarometry of high-pressure metabasites from the Renge and Sanbagawa belts and phase evolution during warm subduction at Nankai
Island Arc ( IF 1.5 ) Pub Date : 2021-05-02 , DOI: 10.1111/iar.12406
David Hernández‐Uribe 1 , Fabián Gutiérrez‐Aguilar 2
Affiliation  

Petrological modeling is a powerful technique to address different types of geological problems via phase-equilibria predictions at different pressure–temperature-composition conditions. Here, we show the versatility of this technique by (1) performing thermobarometrical calculations using phase equilibrium diagrams to explore the petrological evolution of high-pressure (HP) metabasites from the Renge and Sanbagawa belts, Japan and (2) forward-modeling the mineral–melt evolution of the subducted fresh and altered oceanic crust along the Nankai subduction zone geotherm at the Kii peninsula, Japan. In the first case, we selected three representative samples from these metamorphic belts: a glaucophane eclogite and a garnet glaucophane schist from the Renge belt (Omi area) and a quartz eclogite from the Sanbagawa belt (Besshi area). We calculated the peak metamorphic conditions at ~2.0–2.3 GPa and ~550–630 °C for the HP metabasites from the Renge belt, whereas for the quartz eclogite, the peak equilibrium conditions were calculated at 2.5–2.8 GPa and ~640–750 °C. According to our models, the quartz eclogite experienced partial melting after peak metamorphism. In terms of the petrological evolution of the subducted uppermost portion of the oceanic crust along the warm Nankai geotherm, our models show that fluid release occurs at ~20–60 km, likely promoting high pore-fluid pressure, and thus, seismicity at these depths; dehydration is controlled by chlorite breakdown. Our petrological models predict partial melting at >60 km, mainly driven by phengite and amphibole breakdown. According to our models, the melt proportion is relatively small, suggesting that slab anatexis is not an efficient mechanism for generating voluminous magmatism at these conditions. Modeled melt compositions correspond to high-SiO2 adakites; these are similar to compositions found in the Daisen and Sambe volcanoes, in southwest Japan, suggesting that the modeled melts may serve as an analog to explain adakite petrogenesis.

中文翻译:

岩石学建模的多功能性:来自 Renge 和 Sanbagawa 带的高压变变岩的热气压测量和南海暖俯冲期间的相演化

岩石学建模是通过不同压力-温度-成分条件下的相平衡预测来解决不同类型地质问题的强大技术。在这里,我们通过 (1) 使用相平衡图进行热气压计算来探索来自日本 Renge 和 Sanbagawa 带的高压 (HP) 变碱性矿物的岩石学演化以及 (2) 对矿物进行正向建模来展示该技术的多功能性– 沿日本纪伊半岛南海俯冲带地温俯冲的新鲜和蚀变洋壳的熔体演化。在第一个案例中,我们从这些变质带中选择了三个具有代表性的样品:来自 Renge 带(近江地区)的蓝闪榴辉岩和石榴石蓝闪石片岩以及来自 Sanbagawa 带(别子地区)的石英榴辉岩。我们计算了来自 Renge 带的 HP 变玄武岩的峰值变质条件在 ~2.0-2.3 GPa 和 ~550-630 °C,而对于石英榴辉岩,峰值平衡条件计算为 2.5-2.8 GPa 和 ~640-750 ℃。根据我们的模型,石英榴辉岩在峰变质作用后经历了部分熔融。就沿着温暖的南海地温俯冲的洋壳最上部的岩石学演化而言,我们的模型显示流体释放发生在~20-60 公里处,可能促进高孔隙流体压力,从而促进这些深度的地震活动; 脱水由亚氯酸盐分解控制。我们的岩石学模型预测在 >60 公里处部分融化,主要是由闪石和闪石分解驱动。根据我们的模型,熔体比例相对较小,表明在这些条件下板片熔炉并不是产生大量岩浆作用的有效机制。模拟熔体成分对应于高 SiO2埃达克石;这些与在日本西南部的大山和三部火山中发现的成分相似,表明模拟的熔体可以作为解释埃达克岩成因的类似物。
更新日期:2021-06-01
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