Monazite solubility in hydrous silicic melts at high pressure conditions relevant to subduction zone metamorphism
Monazite solubility in hydrous silicic melts at high pressure conditions relevant to subduction zone metamorphism
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DOI：
10.1016/j.epsl.2012.01.002
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发表时间：
2012-03
影响因子：
5.3
通讯作者：
S. Skora;J. Blundy
中科院分区：
文献类型：
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作者：
S. Skora;J. Blundy
将辅助相稳定性应用于俯冲带热结构和过程的关键是了解这些矿物在不同类型俯冲岩石中的热力学稳定性，它们在流体中的溶解度，以及它们对感兴趣的微量元素比例的分馏程度。单独居石是贫钙俯冲沉积物中轻稀土元素（LREE）和钍（Th）的主要载体。相对而言，人们对高压含水熔体（或超临界流体）中独居石的溶解机制知之甚少，但独居石和allanite（海洋玄武岩和一些富cao沉积物中LREE和Th的主要载体）的溶解度最近已被用于量化俯冲板顶温度（Plank， T., Cooper, l.b., Manning, c.e., 2009）。用于估算板坯表面温度的新型地温计。自然地球科学，2,611-615)。我们研究了在俯冲带条件下（3GPa, T≥800°C）的单氮石溶解度。实验结果强调了磷在高压含水硅熔体中对独居石溶解度的重要作用。从热力学上讲，这对应于一种情况下，独居石溶解主要作为其解离组分离子（LREE3+和PO43−）。这与独居石在低压（0.2GPa）下在花岗岩熔体中的溶解度相反，在低压下，独居石似乎主要以伴生的lreepo4物质溶解，因此其溶解度基本上与溶解的磷无关。我们的结果对基于单氮石的测温具有重要意义，因为在高压流体中不考虑磷而引入的误差可能达到100°C。
Critical to any application of accessory phase stability to subduction zone thermal structure and processes is knowledge of the thermodynamic stability of these minerals in different types of subducted rock, their solubility in the presence of fluids, and the extent to which they fractionate trace element ratios of interest. This study focuses on monazite, which is the principal carrier of light rare earth elements (LREE) and thorium (Th) in CaO-poor subducted sediments. Relatively little is known about the mechanism of monazite dissolution in high-pressure hydrous melts (or supercritical fluids), yet monazite and allanite (the principal carrier of LREE and Th in oceanic basalts and some CaO-rich sediments) solubility has been used recently to quantify subducted slab-top temperatures (Plank, T., Cooper, L.B., Manning, C.E., 2009. Emerging geothermometers for estimating slab surface temperatures. Nature Geosci. 2, 611–615). We have studied monazite solubility at subduction zone conditions (3GPa, T≥800°C) in hydrous sediment-melting experiments. Experimental results highlight the important role that phosphorous exerts on monazite solubility in hydrous silicic melts at high pressure. Thermodynamically this corresponds to a case where monazite dissolves predominantly as its dissociated constituent ions (LREE3+and PO43−). This is in contrast to monazite solubility in granitic melts at low pressures (0.2GPa) where it appears to dissolve predominantly as associate LREEPO4species, such that its solubility is essentially independent of dissolved phosphorous. Our results have implications for monazite-based thermometry, as the error introduced by not taking phosphorous into account in high-pressure fluids can amount to >100°C.