(Table 1) Oxygen and hydrogen isotope ratios of hydrothermal altered dolerites from ODP Holes 137-504B and 140-504B

Dolerite samples, recovered in the dike complex between 1589 and 1991 meters below seafloor in Hole 504B during Legs 137/140, have been altered by hydrothermal fluids as shown by the intense replacement of igneous minerals by secondary amphiboles, chlorites, albite, and anorthite. These rocks display a negative correlation between alteration extent and density. This is interpreted in terms of the development of secondary light minerals and an increase in porosity.
For hydrogen, secondary hydroxyl groups (amphibole) dominate over igneous volatiles and control the dD(whole-rock) (-53 per mil to -40 per mil mean = -44 per mil), the D/H fractionation between amphibole (actinolite) and water being about -44 per mil ± 3 per mil at 350°C assuming the fluid has a sea water D/H ratio (dD(fluid) = 0 per mil).
The d18O(whole-rock) values, ranging from 4.7 per mil to 2.7 per mil (mean = 4.1 per mil), are negatively correlated with the abundance of secondary amphiboles, chlorites, and albite (alteration percent) determined by point counting. The comparison of halos related to veins or patches with less altered adjacent parts shows that the process of alteration produces an increase in the amphibole content related to a decrease in the d18O(halo/patch). The halos/patches from the deepest samples in Hole 504B have the lowest d18O(whole-rock) values. This feature can be explained by the progressively decreasing proportion of albite with depth in the dike section. According to Taylor's model, the depletion in 18O of these dolerites (relative to fresh magmatic values: d18O(whole-rock) ~5.7 per mil) is explained by seawater-rock interaction in which the seawater/rock ratio is higher than 0.15 in atomic proportion (~0.3 in mass). Consequently, we deduce that large quantities of seawater-derived fluids have circulated deep in the lower part of the sheeted dike complex of Hole 504B.
The d18O profile in Hole 504B shows a net disequilibrium in the 18O exchange between seawater and the oceanic crust in favor of enrichment in 18O in the seawater. This can be explained by a particular strong expression of high-temperature hydrothermal interaction with seawater-derived fluids at shallow depths (i.e., in Layer 2).

在137/140航次期间，于504B钻孔（Hole 504B）海底以下1589至1991米的岩墙群（dike complex）中采集的辉绿岩（Dolerite）样品，已受热液流体（hydrothermal fluids）蚀变——其证据为火成矿物（igneous minerals）被次生角闪石（secondary amphiboles）、绿泥石（chlorites）、钠长石（albite）及钙长石（anorthite）强烈交代。这些岩石的蚀变程度与密度呈负相关关系，该现象可通过次生轻矿物的形成及孔隙度升高得到解释。

就氢同位素而言，次生羟基基团（hydroxyl groups）赋存于角闪石中，相较于火成挥发分占主导，且控制着全岩δD值（dD(whole-rock)）：范围为-53‰至-40‰，平均值为-44‰。假设流体的氢同位素比值与海水一致（dD(fluid) = 0‰），则在350℃条件下，角闪石（阳起石，actinolite）与水之间的D/H分馏值约为-44‰±3‰。

全岩δ18O值（d18O(whole-rock)）范围为4.7‰至2.7‰，平均值为4.1‰，其与通过点计数法确定的次生角闪石、绿泥石及钠长石的丰度（即蚀变百分含量）呈负相关。将与脉体或斑块相关的蚀变晕（halos）与其邻近弱蚀变区域进行对比后发现，蚀变过程会使角闪石含量升高，同时伴随蚀变晕/斑块的δ18O值降低。504B钻孔最深部样品的蚀变晕/斑块拥有最低的全岩δ18O值。该特征可通过岩墙段中钠长石占比随深度逐渐降低得到解释。根据泰勒（Taylor）模型，这些辉绿岩的18O亏损（相较于新鲜岩浆岩的全岩δ18O值约为5.7‰）是由海水-岩石相互作用造成的，其中原子比例下的海水/岩石比值高于0.15（质量比例约为0.3）。据此我们推断，大量海水来源的流体在504B钻孔席状岩墙群（sheeted dike complex）下部深处发生了循环。

504B钻孔的δ18O剖面（d18O profile）显示，海水与洋壳（oceanic crust）之间的18O交换存在净不平衡，整体表现为海水中的18O富集。这一现象可通过浅部（即第二层，Layer 2）与海水来源流体发生的强烈高温热液相互作用得到解释。