Environmental and chemical controls on palagonitization
Environmental and chemical controls on palagonitization
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巴拉格石化的环境和化学控制
DOI：
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
D. Clague
中科院分区：
文献类型：
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作者：
B. Pauly;P. Schiffman;R. Zierenberg;D. Clague
采用原位显微分析方法，对海底火山碎屑岩、海底火山岩、海相岩浆岩、湖泊岩浆岩和冰下火山环境中的褐铁矿进行了研究，以验证方铅石的成分和结构是否与沉积环境有关。软石化程度与原始孔隙度呈线性负相关，表明孔隙度是软石化的控制因素。反射红外光的吸水率与电子探针测得的水分含量呈线性关系。方铅矿含水率与长方化程度呈线性负相关关系。稀土元素在角闪岩化过程中是不动的，可以用来绘制等温线图来估算主量元素的浓度变化。软石化过程中主要元素和总质量的变化差异很大(特别是FeO和TiO2.)，表明软石化不是一个等体积的过程。这些参数很大程度上依赖于原始的铁锰烷组成，因此在进行全球海洋阳离子通量计算时需要考虑组成。亚碱性铁锰矿在矿化过程中的溶解速度比碱性铁锰矿快得多。埋藏-成岩作用(持续时间较长，低水岩比；被动流体循环)和热液作用(相对短时间，高水岩比；热液循环)是公认的两种长石石化类型。观察到的方铅矿REE浓度梯度表明，铁锰矿的溶解必须在推进的角砾化前锋后面的区域继续进行。研究发现，氧化镁在软化过程中具有很高的流动性。观察到的方铅石氧化镁梯度不是在铁锰矿溶解过程中形成的，而是记录了凝胶-方铅石层向层状硅酸盐转化的开始，这与铁锰矿蚀变层与溶液走向平衡的演化是一致的。
Palagonitized sideromelane from submarine volcaniclastic, seafloor volcanic, marine phreatomagmatic, lacustine phreatomagmatic, and subglacial volcanic settings was investigated using in situ microanalysis to test if palagonite composition and texture are related to depositional environment. Palagonitization extent varies linearly and inversely with original sample porosity, suggesting that porosity is a controlling factor of palagonitization. Water absorbance of reflected infrared light varies linearly with water content derived from electron microprobe totals. Palagonite water content has a linear, inverse relationship to palagonitization extent. REEs are immobile during palagonitization, so they can be used to construct isocon diagrams for estimating major‐element concentration changes. Major‐element and overall mass changes during palagonitization vary widely (particularly for FeO and TiO2) and indicate that palagonitization cannot be an isovolumetric process. These parameters depend strongly on original sideromelane composition, thus requiring composition to be taken into account when performing global oceanic cation flux calculations. Subalkaline sideromelane dissolves much more rapidly than alkaline sideromelane during palagonitization. Two styles of palagonitization, burial‐diagenesis (relatively long‐duration, low water/rock; passive fluid circulation) and hydrothermal (relatively short‐duration, high water/rock; hydrothermal fluid circulation), are recognized. Observed palagonite REE concentration gradients indicate that sideromelane dissolution must continue in the zone behind the advancing palagonitization front. MgO was found to be highly mobile during palagonitization. Observed palagonite MgO gradients are not developed during sideromelane dissolution, but instead record initiation of syn‐ and/or post‐palagonitization conversion of the gel‐palagonite layer to a phyllosillicate layer, consistent with evolution of sideromelane alteration layers toward equilibrium with the solution.