SOLUBILITY OF APATITE, MONAZITE, ZIRCON, AND RUTILE IN SUPERCRITICAL AQUEOUS FLUIDS WITH IMPLICATIONS FOR SUBDUCTION ZONE GEOCHEMISTRY
SOLUBILITY OF APATITE, MONAZITE, ZIRCON, AND RUTILE IN SUPERCRITICAL AQUEOUS FLUIDS WITH IMPLICATIONS FOR SUBDUCTION ZONE GEOCHEMISTRY
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DOI：
10.1098/rsta.1991.0052
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发表时间：
1991-05-15
期刊：
影响因子：
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通讯作者：
WATSON, EB
中科院分区：
文献类型：
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作者：
AYERS, JC;WATSON, EB
测定了副矿物(磷灰石、独居石、锆石和金红石)在超临界流体中的溶解度，以评价这些流体在活化副矿物所含微量元素方面的作用。我们研究了pH、X(H2O)(二氧化碳加入量)、压力(P=1.0-3.0 Gpa)、温度(T=800-1200℃)、溶解硅酸盐和氯化钠浓度对氟磷灰石溶解度的影响。氟磷灰石在纯H2O中的溶解度很低，在所有研究条件下都不超过0.4wt%，但随着pH的降低而急剧增加。P、T、X(H2O)、M(NaC L)(氯化钠的摩尔分数)和溶解硅酸盐浓度的变化对磷灰石的溶解度影响相对较小。独居石在水中的溶解度更低(不超过0.2wt%)。有限的数据表明，独居石的溶解度随着P和T的增加而增加，随pH的降低而增加，但对M(NaC L)不敏感。锆石与H2O反应形成斜方石(ZrO2)+富硅流体。ZrO2在H2O和1M HCl中的溶解度小于0.2wt%。在石英饱和流体+/-HCl+/-氯化钠和在H2O-CO2流体中的溶解度也很低。在wt%范围内，金红石比其他矿物更易溶解，且其溶解度随着P和T的增加而增加。结果表明，高P-T水溶液可以溶解大量的钛，但极少的锆离子，也很少的磷酸盐，除非溶液是酸性的。在大多数情况下，在水流体交代过程中，磷灰石、独居石和锆石仍将存在，因此将作为残留物相对元素分布进行控制。在高压下，金红石相对于其他副矿物具有较高的溶解度，这可能导致在俯冲带火山岩中观察到的高场强元素相对于大离子亲石元素的贫化。
Solubilities of accessory minerals (apatite, monazite, zircon and rutile) in supercritical aqueous fluids have been measured to evaluate the role of these fluids in the mobilization of accessory mineral-hosted trace elements. We have characterized the effects on solubility of pH, X(H2O) (addition of CO2), pressure (P = 1.0-3.0 GPa), temperature (T = 800-1200-degrees-C), and dissolved silicate and NaCl concentration.Fluorapatite solubility in pure H2O is low, not more than 0.4 wt% at all conditions studied, but increases strongly with decreasing pH. Changes in P, T, X(H2O), M(NaCl) (the molality of NaCl), and dissolved silicate concentration have comparatively little effect on apatite solubility. Monazite is even less soluble in H2O (not more than 0.2 wt%). Limited data suggests that monazite solubility increases with increasing P and T and with decreasing pH, but is insensitive to M(NaCl).Zircon reacts with H2O to form baddeleyite (ZrO2) + silica-rich fluid. ZrO2 solubility in H2O and 1 M HCl is less than 0.2 wt%. Zircon, and therefore ZrO2, solubility in quartz-saturated fluids +/- HCl +/- NaCl and in H2O-CO2 fluids is also very low. Rutile is more soluble than the other minerals examined, in the wt% range, and its solubility increases with increasing P and T.Results indicate that high P-T aqueous fluids can dissolve significant amounts of Ti but very little Zr, and little phosphate unless the fluids are acidic. In most cases, apatite, monazite and zircon will remain present during episodes of aqueous fluid metasomatism and therefore will exert control, as 'residual phases', over element distribution. The higher solubility of rutile relative to other accessory minerals at high pressure may result in the depletion of high field strength elements relative to large ion lithophile elements observed in subduction zone volcanics.