Mechanisms of alteration of basaltic and rhyolitic glasses considering solution chemistry and passivating properties of palagonite - a case study on ICDP drilling sites Hawaii and Snake River Plain

玄武岩和流纹岩玻璃上的蚀变层在火山岩中很常见。这些层被称为palagonite，对玻璃向结晶相的转变以及玻璃与其他岩石成分或流体的反应有很强的影响，后者对元素释放具有重要意义。特别是palagonite可以作为扩散屏障，减缓甚至抑制玻璃化。由于聚合和沉淀反应会影响孔隙度和渗透率，这种屏障的作用可能会随着时间的推移而改变。在玄武岩玻璃表面形成凹坑和管状的微生物也可能为palagonite提供通道，从而增强非生物玻璃蚀变。关于蚀变层孔隙度和非平衡结构的发现，以及界面耦合溶解再沉淀机制的新模型，鼓励我们利用蚀变玻璃样品结合实验工作来确定玻璃蚀变与palagonite性质之间的关系，特别是层孔隙度和溶液化学对玻璃风化速率的影响。夏威夷和斯内克河平原暴露在盐水和不同的淡水中，温度允许微生物定植，从ICDP钻井岩心中获得化学上不同的玄武岩和流纹岩玻璃将包括在内。我们计划的研究包括：(i)以结构为重点的玻璃蚀变岩相学研究；（ii）利用氮气吸附、汞孔隙法、熔融合金浸渍和各种显微技术表征孔隙系统；（iii）孔空间运输的实验研究；（iv）考虑生化因素，通过ζ电位和元素释放率来确定离子对玻璃溶解的影响。（五）在与钻井现场相关的条件下进行流体玻璃实验。需要了解这些相互作用，以了解和预测palagonite形成，玻璃蚀变率，溶液组成和生化因素的相互依赖性。

Alteration layers on basaltic and rhyolitic glasses are common in volcanic rocks. Such layers denoted as palagonite have strong influence on transformation of glasses to crystalline phases and reactions of glasses with other rock components or fluids, the latter being of great importance for element release. In particular palagonite may act as diffusion barrier that slows down or even inhibit glass alteration. The effect of such a barrier may change over time due to polymerization and precipitation reactions which affect porosity and permeability. Microorganisms forming pits and tubes in basaltic glass surfaces may provide routes in palagonite which enhance abiotic glass alteration too. Findings on porosity and nonequilibrium textures in alteration layers, and a new model on an interface-coupled dissolution reprecipitation mechanism encouraged us to use altered glass samples in combination with experimental work to determine the relationship between glass alteration and palagonite properties, in particular effects of porosity of layers and solution chemistry on glass weathering rate. Chemically different basaltic and rhyolitic glasses available from ICDP drilling cores Hawaii and Snake River Plain exposed to saline and different fresh waters at temperatures allowing microbial colonization will be included. Our planned research involves (i) a petrographical investigation of glass alteration with focus on texture, (ii) the characterization of pore systems using N2-adsorption, Hg-porosimetry, impregnation with a molten alloy and various microscopic techniques, (iii) an experimental study of transport in pore spaces, (iv) determination of ionic effects on glass dissolution traced by zeta-potential and element release rates considering biochemical factors, and (v) fluid-glass experiments at conditions relevant to the drilling sites. Knowledge of these interactions is needed to understand and predict interdependencies of palagonite formation, glass alteration rates, solution composition and biochemical factors.