Chemistry of phyllosilicates of ODP Hole 140-504B

Replacement minerals in olivine record the evolution of hydrothermal alteration between 1600 and 2000 mbsf in the sheeted dike complex in Hole 504B.
1. Talc (+ magnetite) rim on olivine represents the earliest alteration. Talc probably crystallized during initial cooling of the dikes.
2. The partial breakdown of talc to "deweylite", a chaotic mixture of serpentine and Al-free stevensite, was facilitated by further cooling and a somewhat increased fluid:rock interaction in the dikes.
3. The presence of chlorite veins and the replacement of unaltered olivine cores, talc, and deweylite and of other silicates by chlorite suggest fracturing of the rocks during cooling (shrinkage cracks) and local influx of seawater into the dikes.
4. Late amphibole veins and locally extensive amphibole alteration indicate increasing temperature and the development of new sets of fractures, possibly due to the injection of fresh magma.
Several generations of chlorite and amphibole veins are present in the dikes. Offset veins and the crack-seal texture within veins in the dikes suggest that the alteration cycle was probably repeated with the injection of each set of new dikes.
Presently measured temperatures (195°C) at 2000 m depth in Hole 504B indicate that deweylite, which was previously considered a low-temperature mineral, can form well above its previously estimated crystallization temperature of 50°C.

橄榄石（olivine）中的交代矿物记录了504B钻孔（Hole 504B）席状岩墙群（sheeted dike complex）内，1600至2000 mbsf区间内热液蚀变（hydrothermal alteration）的演化过程。
1. 橄榄石表面的滑石（talc）与磁铁矿（magnetite）边代表了最早一期蚀变。滑石大概率形成于岩墙的初始冷却阶段。
2. 滑石向‘迪魏石（deweylite）’发生部分分解，后者是蛇纹石（serpentine）与无铝斯文石（stevensite）的无序混合体；该过程因岩墙进一步冷却，以及流体-岩石相互作用强度略有增强而得以促进。
3. 绿泥石（chlorite）脉体的产出，以及未蚀变橄榄石核心、滑石、迪魏石与其他硅酸盐被绿泥石交代的现象，均指示岩石在冷却过程中发生破裂（形成收缩裂隙（shrinkage cracks）），且海水局部涌入岩墙群。
4. 晚期角闪石（amphibole）脉体以及局部广泛发育的角闪石蚀变，指示温度升高与新裂隙组的形成，这一过程可能与新鲜岩浆（magma）的注入有关。
岩墙群中存在多期次的绿泥石与角闪石脉体。错动脉体（offset veins）以及岩墙内脉体的裂纹密封构造（crack-seal texture）均表明，随着每一期新岩墙的注入，蚀变循环大概率重复发生。
目前在504B钻孔2000米深度测得的温度（195℃）表明，此前被视为低温矿物的迪魏石，其形成温度可远高于此前估算的50℃结晶温度。