10. FROM OXIDIZING TO REDUCING ALTERATION: MINERALOGICAL VARIATIONS IN PILLOW BASALTS FROM THE EAST FLANK, JUAN DE FUCA RIDGE 1
10. FROM OXIDIZING TO REDUCING ALTERATION: MINERALOGICAL VARIATIONS IN PILLOW BASALTS FROM THE EAST FLANK, JUAN DE FUCA RIDGE 1
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10. 从氧化蚀变到还原蚀变：胡安德富卡海岭东侧枕状玄武岩的矿物学变化 1
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发表时间：
2000
期刊：
影响因子：
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通讯作者：
R. Cabella
中科院分区：
文献类型：
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作者：
P. Marescotti;D. Vanko;R. Cabella
在此基础上，研究了0.8 ~ 3.5 Ma正常拉斑枕玄武岩低温（<100℃）蚀变的矿物学特征。它们的蚀变强度有系统的变化，与以下几个因素有关：(1)火成岩地壳的老化；(2)沉积物/基底界面处测量的较年轻到较老地点的温度升高；(3)局部和区域的岩性和原生孔隙度变化；(4)枕状断裂的程度。裂缝是流体进入岩石的最重要的通道，也是控制玻璃状边缘变化和枕状变化早期阶段的唯一因素。划分出三个不同的蚀变阶段：玻璃质边缘蚀变阶段、裂缝系统流体循环作用下的氧化蚀变阶段和扩散作用下的还原蚀变阶段。所有观察到的发生在蚀变早期阶段的矿物学和化学变化都被解释为岩石与“正常”、碱性和氧化海水相互作用的结果，沿着同心和径向裂缝系统所代表的优先路径。流体的化学成分在进入玄武岩的过程中逐渐演变，导致还原蚀变阶段，这一阶段最初是富铁皂石和少量硫化物的沉淀，随后是碳酸盐的广泛形成。与此同时，该系统从“水为主”演变为“岩石为主”。没有观察到枕状玄武岩的蚀变效应，这些蚀变效应必须发生在高于第168号试验期间在基底/沉积物界面测量的温度下（例如，在15°至64°C之间）。
With this study, we investigate the mineralogical variations associated with the low-temperature (<100°C) alteration of normal tholeiitic pillow basalts varying in age from 0.8 to 3.5 Ma. Their alteration intensity varies systematically and is related to several factors, including (1) the aging of the igneous crust, (2) the increase of temperatures from the younger to the older sites, measured at the sediment/basement interface, (3) the local and regional variations in lithology and primary porosity, and (4) the degree of pillow fracturing. Fractures represent the most important pathways that allow significant penetration of fluids into the rock and are virtually the only factor controlling the alteration of the glassy rim and the early stages of pillow alteration. Three different alteration stages have been recognized: alteration of glassy margin, oxidizing alteration through fluid circulation in fracture systems, and reducing alteration through diffusion. All the observed mineralogical and chemical variations occurring during the early stages of alteration are interpreted as the result of the rock interaction with “normal,” alkaline, and oxidizing seawater, along preferential pathways represented by the concentric and radial crack systems. The chemical composition of the fluid progressively evolves while moving into the basalt, leading to a reducing alteration stage, which is initially responsible for the precipitation of Fe-rich saponite and minor sulfides and subsequently for the widespread formation of carbonates. At the same time, the system evolved from being “water dominated” to being “rock dominated.” No alteration effects in pillow basalts were observed that must have occurred at temperatures higher than those measured during Leg 168 at the basement/sediment interface (e.g., between 15° and 64°C).