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首页> 外文期刊>Contributions to Mineralogy and Petrology >Stability and chemical equilibrium of amphibole in calc-alkaline magmas: an overview, new thermobarometric formulations and application to subduction-related volcanoes
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Stability and chemical equilibrium of amphibole in calc-alkaline magmas: an overview, new thermobarometric formulations and application to subduction-related volcanoes

机译：钙碱性岩浆中闪石的稳定性和化学平衡：概述，新的热压公式及其在俯冲相关火山中的应用

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摘要

This work focuses on a rigorous analysis of the physical–chemical, compositional and textural relationships of amphibole stability and the development of new thermobarometric formulations for amphibole-bearing calc-alkaline products of subduction-related systems. Literature experimental results (550–1,120°C, 0.21) and are inferred to represent xenocrysts of crustal or mantle materials. Most experimental results on calc-alkaline suites have been found to be unsuitable for using in thermobarometric calibrations due to the high Al# (>0.21) of amphiboles and high Al2O3/SiO2 ratios of the coexisting melts. The pre-eruptive crystallization of consistent amphiboles is confined to relatively narrow physical–chemical ranges, next to their dehydration curves. The widespread occurrence of amphiboles with dehydration (breakdown) rims made of anhydrous phases and/or glass, related to sub-volcanic processes such as magma mixing and/or slow ascent during extrusion, confirms that crystal destabilization occurs with relatively low T–P shifts. At the stability curves, the variance of the system decreases so that amphibole composition and physical–chemical conditions are strictly linked to each other. This allowed us to retrieve some empirical thermobarometric formulations which work independently with different compositional components (i.e. Si*, AlT, Mg*, [6]Al*) of a single phase (amphibole), and are therefore easily applicable to all types of calc-alkaline volcanic products (including hybrid andesites). The Si*-sensitive thermometer and the fO2–Mg* equation account for accuracies of ±22°C (σest) and 0.4 log units (maximum error), respectively. The uncertainties of the AlT-sensitive barometer increase with pressure and decrease with temperature. Near the P–T stability curve, the error is 35%) and lower-T magmas, the uncertainty increases up to 24%, consistent with depth uncertainties of 0.4 km, at 90 MPa (~3.4 km), and 7.9 km, at 800 MPa (~30 km), respectively. For magnesiohornblendes, the [6]Al*-sensitive hygrometer has an accuracy of 0.4 wt% (σest) whereas for magnesiohastingsite and tschermakitic pargasite species, H2Omelt uncertainties can be as high as 15% relative. The thermobarometric results obtained with the application of these equations to calc-alkaline amphibole-bearing products were finally, and successfully, crosschecked on several subduction-related volcanoes, through complementary methodologies such as pre-eruptive seismicity (volcano-tectonic earthquake locations and frequency), seismic tomography, Fe–Ti oxides, amphibole–plagioclase, plagioclase–liquid equilibria thermobarometry and melt inclusion studies. A user-friendly spreadsheet (i.e. AMP-TB.xls) to calculate the physical–chemical conditions of amphibole crystallization is also provided.
机译：这项工作的重点是对闪石稳定性的物理，化学，成分和质地关系进行严格分析，并为俯冲相关系统中含闪石的钙碱性产品开发新的热压配方。文献实验结果（550–1,120°C，0.21）被推断为代表地壳或地幔物质的异晶。已发现大多数钙碱性化合物的实验结果都不适合用于热压法校准，这是由于两闪石的Al＃（> 0.21）高和Al 2 O 3 / SiO 2 比。稳定的闪石的喷发前结晶仅限于相对较窄的物理化学范围，紧随其脱水曲线。由无水相和/或玻璃制成的带有脱水（破裂）边缘的闪石的广泛出现，与岩浆混合和/或挤压过程中缓慢上升等次火山过程有关，这证实了晶体的失稳发生在相对较低的TP位移下。在稳定性曲线上，系统的方差减小，从而使闪石的成分和物理化学条件相互严格关联。这使我们能够检索一些经验性的气压计公式，这些公式可独立于不同的成分组分（例如，Si * ，Al T ，Mg * ， [6] Al * ）的单相（amphibole），因此很容易适用于所有类型的钙碱性火山岩产品（包括混合安山岩）。 Si * 温度计和fO 2 –Mg * 方程的精度为±22°C（σ est < / sub>）和0.4对数单位（最大误差）。 Al T 敏感气压计的不确定度随压力增加而随温度降低。在P–T稳定曲线附近，误差为35％），而在较低的T岩浆附近，不确定度增加到24％，与深度不确定度0.4 km（在90 MPa（〜3.4 km）和7.9 km）一致。分别为800 MPa（〜30 km）。对于镁尖晶石混合物， [6] Al * 敏感型湿度计的准确度为0.4 wt％（σ est ），而对于镁镁混纺棉和切克玛奇克石棉种类中，H 2 O 熔体不确定性相对可高达15％。最后，通过补充方法，如喷发前的地震活动性（火山构造地震的位置和频率），将这些方程式应用于含钙碱性闪石的产品的热气压结果最终成功地进行了交叉核对。 ，地震层析成像，Fe-Ti氧化物，角闪石-斜长石，斜长石-液体平衡热压法和熔体包裹体研究。还提供了一个用户友好的电子表格（即AMP-TB.xls）来计算闪石结晶的物理化学条件。

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