Experimental determination of H2O–NaCl liquidi to 25 mass% NaCl and 1.4 GPa: Application to the Jovian satellite Europa
Experimental determination of H2O–NaCl liquidi to 25 mass% NaCl and 1.4 GPa: Application to the Jovian satellite Europa
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实验%20测定%20of%20H2OâNaCl%20liquidi%20to%2025%20mass%%20NaCl%20and%201%204%20GPa:%20应用%20to%20the%20Jovian%20satellite%20欧洲
DOI：
10.1016/j.gca.2012.06.007
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发表时间：
2012
影响因子：
5
通讯作者：
Schmidt C.
中科院分区：
文献类型：
--
作者：
Valenti P;Bodnar R.J;Schmidt C.
用高压光室或水热金刚石对顶砧室结合拉曼光谱，对体相组成为5，10，15和25mass%NaCl的H_2O +NaCl体系在压力≤ 1.4GPa下的液相进行了实验测定。冰I液相线的dP/dT斜率随着盐度的增加而变陡，即，它从纯H2O的10 - 9 MPa/°C降低到5和10mass%NaCl的10 - 11 MPa/°C，以及15mass%NaCl的10 - 15 MPa/°C。在较高压力下，其它固相的liquidi总是显示正的dP/dT斜率。5mass%NaCl液体的dP/dT斜率与相应的纯水冰融化曲线的dP/dT斜率相似，但冰稳定性场向高压方向移动，例如，冰I+冰III+液体三相点的压力为209.9MPa，温度为-27.7 °C（纯水的压力为-21.985 °C）。在15mass%NaCl时，水卤石液相线取代了冰III和冰V液相线，并且还减小了冰I稳定的压力范围。对于15mass%NaCl，三重点的大致P-T位置对于水卤石+冰VI+液体为1.07GPa和1.7°C，对于冰I+水卤石+液体为25 MPa和−11.7°C（作为比较，冰I+水卤石+L+V四重不变点为−21.2°C，0.0001MPa，23.15mass%NaCl）。冰VI的稳定性领域不断转向更高的压力，另外高达25mass%的NaCl，可能只有很小的变化，在液相线的dP/dT斜率。在25mass%NaCl下，水卤石液相线从0.1MPa延伸到更高的压力，并且在140± 40 MPa和140 - 7.5°C下显示出dP/dT斜率从负到正的变化，这表明含水液体的动态结构发生了变化。本文报道了15或25mass%NaCl溶液在高压下冷冻形成的一种柱状晶习性的未知相的拉曼光谱。该相在O-H伸缩区的拉曼光谱的特征是在3410、3460和3510 cm-1处有三个谱带，与任何冰相或水卤石都不匹配。根据本文测定的H_2O +NaCl体系中的液相量和文献中计算的温度剖面，假定NaCl为主要溶质，估计木卫二上覆盖在含水液体地幔上的冰壳厚度约为9 km。此外，我们的液相线数据表明，最大的NaCl浓度约为15-20mass%的NaCl和最低的次表层海洋温度为260 K。
Liquidi in the system H2O+NaCl were determined experimentally for bulk compositions of 5, 10, 15, and 25mass% NaCl at pressures to ∼1.4GPa using a high-pressure optical cell or a hydrothermal diamond-anvil cell combined with Raman spectroscopy. The dP/dT slope of the ice I liquidus becomes steeper with increasing salinity, i.e., it decreases from ∼−9MPa/°C for pure H2O, to ∼−11MPa/°C for 5 and 10mass% NaCl, and to ∼−15MPa/°C for 15mass% NaCl. The liquidi for other solid phases at higher pressures always display a positive dP/dT slope. The liquidi of 5mass% NaCl have dP/dT slopes similar to those of the corresponding ice melting curves of pure H2O, but the ice stability fields shift towards higher pressures, e.g., the ice I+ice III+liquid triple point was observed at ∼300MPa and −27.7°C (that of pure water is at 209.9MPa and −21.985°C). At 15mass% NaCl, a hydrohalite liquidus replaces the ice III and ice V liquidi, and also decreases the range in pressure of ice I stability. Approximate P–T locations of triple points for 15mass% NaCl are ∼1.07GPa and 1.7°C for hydrohalite+ice VI+liquid, and ∼25MPa and −11.7°C for ice I+hydrohalite+liquid (for comparison, the ice I+hydrohalite+L+V quadruple invariant point is at −21.2°C, ∼0.0001MPa, 23.15mass% NaCl). The stability field of ice VI shifts continuously towards higher pressure with addition of up to 25mass% NaCl, with probably only small changes in the dP/dT slope of the liquidus. At 25mass% NaCl, the hydrohalite liquidus extends from 0.1MPa to higher pressure and shows a change in the dP/dT slope from negative to positive at ∼−7.5°C and ∼140±40MPa, which suggests a change in the dynamic structure of the aqueous liquid. Raman spectra of an unknown phase of columnar crystal habit are reported, which formed upon freezing of 15 or 25mass% NaCl solutions at high pressure. The Raman spectrum of this phase in the O–H stretching region is characterized by three bands at ∼3410, ∼3460, and ∼3510cm−1, and does not match any of the ice phases or hydrohalite. Based on the liquidi in the H2O+NaCl system determined in this study and a calculated temperature profile from the literature, the icy shell overlying an aqueous liquid mantle on the Jovian satellite Europa is estimated to be about 9km thick, assuming NaCl as the predominant solute. Furthermore, our liquidus data suggest a maximum NaCl concentration of about 15–20mass% NaCl and a minimum subsurface ocean temperature of ∼260K.
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