(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.