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首页> 外文期刊>Contributions to Mineralogy and Petrology >Experimental determination of liquidus - H2O contents of haplogranite at deep-crustal conditions
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Experimental determination of liquidus - H2O contents of haplogranite at deep-crustal conditions

机译：深层地壳条件下液相质 - H2O含量的实验测定

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摘要

The liquidus water content of a haplogranite melt at high pressure (P) and temperature (T) is important, because it is a key parameter for constraining the volume of granite that could be produced by melting of the deep crust. Previous estimates based on melting experiments at low P (<= 0.5 GPa) show substantial scatter when extrapolated to deep crustal P and T (700-1000 degrees C, 0.6-1.5 GPa). To improve the high-P constraints on H2O concentration at the granite liquidus, we performed experiments in a piston-cylinder apparatus at 1.0 GPa using a range of haplogranite compositions in the albite (Ab: NaAlSi3O8)-orthoclase (Or: KAlSi3O8)-quartz (Qz: SiO2)-H2O system. We used equal weight fractions of the feldspar components and varied the Qz between 20 and 30 wt%. In each experiment, synthetic granitic composition glass + H2O was homogenized well above the liquidus T, and T was lowered by increments until quartz and alkali feldspar crystalized from the liquid. To establish reversed equilibrium, we crystallized the homogenized melt at the lower T and then raised T until we found that the crystalline phases were completely resorbed into the liquid. The reversed liquidus minimum temperatures at 3.0, 4.1, 5.8, 8.0, and 12.0 wt% H2O are 935-985, 875-900, 775-800, 725-775, and 650-675 degrees C, respectively. Quenched charges were analyzed by petrographic microscope, scanning electron microscope (SEM), X-ray diffraction (XRD), and electron microprobe analysis (EMPA). The equation for the reversed haplogranite liquidus minimum curve for Ab(36.25)Or(36.25)Qz(27.5) (wt% basis) at 1.0 GPa is (T = - 0.0995 W-H2(o)2 - 88.183w(H2)O + 1171.0 for 0 <= w(H2)O <= 17 wt% and T is in C. We present a revised P - T diagram of liquidus minimum H2O isopleths which integrates data from previous determinations of vapor-saturated melting and the lower pressure vapor-undersaturated melting studies conducted by other workers on the haplogranite system. For lower H2O (<5.8 wt%) and higher temperature, our results plot on the high end of the extrapolated water contents at liquidus minima when compared to the previous estimates. As a consequence, amounts of metaluminous granites that can be produced from lower crustal biotite-amphibole gneisses by dehydration melting are more restricted than previously thought.
机译：高压（P）和温度（T）在高压（P）和温度（T）中的液相含水量是重要的，因为它是约束通过熔化深外壳产生的花岗岩体积的关键参数。基于低P（<= 0.5GPa）的熔化实验的先前估计显示在外推到深色地壳P和T（700-1000摄氏度，0.6-1.5GPa）时显示出实质的散射。为了改善花岗岩液中H2O浓度对H 2 O浓度的高p约束，我们使用Albate（Ab：Naalsi3O8）中的一系列Haplogranite组合物在1.0GPa处的活塞缸装置中进行了实验（Ab：Naalsi3O8） - 乙基酶（或：Kalsi3O8）-quartz （QZ：SiO2）-H2O系统。我们使用平庸组件的相等体重，并在20至30wt％之间变化。在每个实验中，合成的花岗岩组合物玻璃+ H2O在液相高于液体T上均匀化，通过增量降低T直至从液体结晶的石英和碱金属石。为了建立逆转平衡，我们将均质化熔体结晶，然后升高，直到发现结晶相完全吸收到液体中。在3.0,4.1,5.8,80和12.0wt％H 2 O下的反向液体最小温度分别为935-985,875-900,775-800,725-775和650-675摄氏度。通过岩体显微镜，扫描电子显微镜（SEM），X射线衍射（XRD）和电子微探测分析（EMPA）分析淬火电荷。用于AB（36.25）或（36.25）Qz（27.5）Qz（27.5）（27.5）（27.5）（27.5）的液体最小曲线（27.5）（27.5）（Wt％）（T = - 0.0995W-H2（O）2 - 88.183W（H2）O. + 1171.0对于0 <= W（H2）O <= 17wt％和T在C中。我们介绍了一种修正的p-T图，其液相液的最小H2O Isopleth，其将数据与蒸汽饱和熔化的先前测定集成在一起和较低压力储华沉积的熔融研究由其他工人进行的Haplogranite系统进行。对于低温（<5.8wt％）和更高的温度，与先前的估计相比，我们的结果在液相次数最小的外推水含量的高端。如结果，通过脱水熔化可以由下地壳生物素 - 倍铬根茎生产的金属滤片量的量比以前认为更受限制。

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