(Table 1) Magnetic properties of basalt samples, at DSDP Legs 69 and 70

We studied magnetic properties of basalts from cores of Sites 504 (mainly Hole 504B) and 505. According to magnetic and petrographic data, the basalts are altered to different degrees. We determined the ratio Ist/Iso and the Curie points of the basalts. In Hole 504B there is vertical zoning of titanomagnetite alteration: in the upper part of the basement, low temperature titanomaghemitization predominates (IST/Iso > 1); in the lower part of the hole, multi-phase alteration (IST/Iso < 1) predominates. This is evidence for superimposition of multi-phase alteration after single-phase oxidation. The latter process occurred at low temperatures. Multi-phase alteration is represented by exsolution and unmixing of titanomagnetite. Its appearance is connected with extended secondary heating at temperatures of about 100°C, documented by thermal measurements in the hole. Magnetic properties of basalts from Site 505 are typical of submarine pillow lavas that contain fine-grained titanomaghemite.

本研究针对504站位（主要涵盖504B钻孔）与505站位的岩芯玄武岩开展磁学性质分析。基于磁学与岩石学测试数据，该类玄武岩存在不同程度的蚀变现象。我们测定了其Ist/Iso比值与居里点（Curie points）。504B钻孔内的钛磁铁矿（titanomagnetite）蚀变呈现垂直分带特征：基底上部以低温钛磁赤铁矿化为主，此时Ist/Iso＞1；钻孔下部则以多期蚀变占主导，此时Ist/Iso＜1。该现象指示，单相氧化作用（该过程发生于低温环境）之后叠加了多期蚀变过程。多期蚀变表现为钛磁铁矿的出溶与析离作用，其形成与约100℃的持续性次生加热密切相关，这一结论已得到钻孔热测数据的佐证。505站位玄武岩的磁学性质，与赋存细粒钛磁赤铁矿（titanomaghemite）的海底枕状熔岩的典型特征相符。