Geochemistry and effect of oxidation state of iron at DSDP Leg 69 Holes

Over 300 electron microprobe and wet chemical analyses were made of alteration minerals (mostly clays) in basalts from DSDP Sites 501, 504, and 505 in the Costa Rica Rift. These analyses are displayed using a three-dimensional graphical method. Several alteration minerals have been identified, of which saponites are by far the most common. In situ alteration of basalt glass has produced montmorillonite-like minerals rich in the less-mobile elements such as Al and Ti. Talc-like minerals commonly replace olivine and act as fillings to vesicles. Three other alteration minerals have been recognized chemically, rich in Na and Ca, but these are presently unidentified. There is no evidence for systematic change of mineral chemistry with depth.

针对哥斯达黎加裂谷（Costa Rica Rift）深海钻探计划（Deep Sea Drilling Project）501、504及505站位的玄武岩蚀变矿物（以黏土类为主），研究人员共完成了300余组电子探针（electron microprobe）与湿化学分析。本次分析采用三维绘图法进行结果可视化展示。研究已识别出多种蚀变矿物，其中皂石（saponite）为绝对优势矿物。玄武岩玻璃的原位蚀变作用生成了富含铝、钛等难迁移元素的类蒙脱石矿物。滑石类矿物通常交代橄榄石，并充填于玄武岩气孔之中。经化学表征还发现3种富钠钙的蚀变矿物，但目前尚未完成矿物鉴定。未发现矿物化学组成随深度呈现系统性变化的相关证据。