Geochemical composition and atomic formulas of saponites, celadonites and carbonates from ODP Leg 168 sites@en

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. […]本研究针对形成年代介于0.8至3.5百万年（Ma）的普通拉斑玄武质（tholeiitic）枕状玄武岩（pillow basalts），探究其在低温（<100℃）蚀变过程中伴随的矿物学变化。该类玄武岩的蚀变强度呈现系统性变化，且与多项控制因素相关：(1) 火成地壳的成熟演化；(2) 沉积物-基底界面处实测温度随点位年代由新至老逐渐升高；(3) 岩性与原生孔隙度的局域及区域差异；(4) 枕状岩体的破裂程度。裂隙是流体大规模渗入岩体的最主要通道，实际上也是控制玻璃质边缘蚀变及枕状岩体早期蚀变阶段的唯一因素。目前已识别出三种不同的蚀变阶段：玻璃质边缘蚀变、裂隙系统流体循环驱动的氧化蚀变，以及扩散作用主导的还原蚀变。[…]