Evolution of palagonite: Crystallization, chemical changes, and element budget
Evolution of palagonite: Crystallization, chemical changes, and element budget
复制标题
DOI：
10.1029/2000gc000102
复制
发表时间：
2001-07
期刊：
影响因子：
3.7
通讯作者：
N. Stroncik;H. Schmincke
中科院分区：
文献类型：
--
作者：
N. Stroncik;H. Schmincke
通过应用一系列分析方法（电子探针、红外光度法、原子力显微镜、X射线荧光和X射线衍射），研究了斜长岩的结构和化学演化与玻璃成分、蚀变环境和时间的关系。火山玻璃的钾长石化作用是一个玻璃溶解、钾长石形成和钾长石演化的连续过程，可分为元素迁移率变化的两个不同反应阶段。第一阶段的特征是玻璃的同成分溶解和“新鲜”、凝胶状、无定形、光学各向同性、主要为淡黄色的斜长岩的同时沉淀。这一阶段伴随着Si、Al、Mg、Ca、Na、K等元素的损失，H2O的主动富集，以及Ti、Fe的被动富集。第二阶段是一个老化过程，在此过程中，矿物不稳定的斜长岩与周围的流体反应并结晶成蒙皂石。该阶段伴随着从溶液中吸收Si、Al、Mg和K以及Ti和H2O的损失。Ca和Na仍然显示出损失，而Fe的反应不太一致，保持不变或显示出损失。元素迁移的程度和方向在斜长岩化过程中发现，主要是不同的斜长岩老化，一旦第一沉淀的斜长岩发生。这一点通过不同老化步骤的斜长岩的主要元素特征的对比、斜长岩老化过程中元素迁移方向的变化以及斜长岩中随着结晶物质形成的增加，元素损失总体减少来表明。考虑到水-岩系统的整体元素收支，玻璃转化为斜长岩所伴随的元素损失比整个蚀变过程（包括第二相的形成和斜长岩老化）大得多。最不发达的palagonitized镁铁质玻璃研究经历了多达65重量%的损失的元素在palagonite形成过程中，相比之下，28重量%的元素损失在散装蚀变。大约33%（重量）的元素损失计算出一个更进化的，在老化程度方面，岩石研究，相比之下，几乎没有损失的散装蚀变。
The structural and chemical evolution of palagonite was studied as a function of glass composition, alteration environment, and time by applying a range of analytical methods (electron microprobe, infrared photometry, atomic force microscopy, X‐ray fluorescence, and X‐ray diffraction). Palagonitization of volcanic glass is a continuous process of glass dissolution, palagonite formation, and palagonite evolution, which can be subdivided into two different reaction stages with changing element mobilities. The first stage is characterized by congruent dissolution of glass and contemporaneous precipitation of “fresh,” gel‐like, amorphous, optically isotropic, mainly yellowish palagonite. This stage is accompanied by loss of Si, Al, Mg, Ca, Na, and K, active enrichment of H2O, and the passive enrichment of Ti and Fe. The second stage is an aging process during which the thermodynamically unstable palagonite reacts with the surrounding fluid and crystallizes to smectite. This stage is accompanied by uptake of Si, Al, Mg, and K from solution and the loss of Ti and H2O. Ca and Na are still showing losses, whereas Fe reacts less consistently, remaining either unchanged or showing losses. The degree and direction of element mobility during palagonitization was found to vary mainly with palagonite aging, as soon as the first precipitation of palagonite occurs. This is indicated by the contrasting major element signatures of palagonites of different aging steps, by the changes in the direction of element mobility with palagonite aging, and by the general decrease of element loss with increasing formation of crystalline substances in the palagonite. Considering the overall element budget of a water‐rock system, the conversion of glass to palagonite is accompanied by much larger element losses than the overall alteration process, which includes the formation of secondary phases and palagonite aging. The least evolved palagonitized mafic glass studied has undergone as much as 65 wt% loss of elements during palagonite formation, compared to ∼28 wt% element loss during bulk alteration. ABout 33 wt% element loss was calculated for one of the more evolved, in terms of the aging degree, rocks studied, compared to almost no loss for bulk alteration.