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Magnetic measurements were made on 67 basalt samples from Sites 250, 251, 253, 254, 256, and 257 of Leg 26, Deep Sea Drilling Project. Paleolatitudes estimated from the inclinations after alternating-field demagnetization at 100 oe are compatible with apparent polar wandering curves (except Site 256) and reconstructions of the Indian Ocean based on lineated magnetic anomalies (except Sites 250 and 256). The samples displayed low coercivities (95-oe average median destructive field), except at Site 254 (383-oe median destructive field). Intensities of natural remanent magnetization are lower than are typical of dredged basalts, and low-field susceptibilities are higher. Viscous remanent magnetization was shown experimentally to be high in many specimens and could account for a large portion of their original intensity. Low coercivities, high viscous remanence, and the limited number of flows sampled all detract from the statistical confidence of the paleolatitude estimates. Site 257 revealed a polarity reversal, which can most likely be attributed to a thin dike or sill injected during a reversed episode subsequent to the emplacement and cooling of the rest of the cored section, which is normally polarized. INTRODUCTION Since the tectonic motions of the plates in the Indian Ocean were both rapid and extensive and as they are not yet well understood east of the Ninetyeast Ridge, reliable paleolatitude determinations from there would be valuable. Leg 26 of the Deep Sea Drilling Project recovered long sections of cored basalt from six sites in the Indian Ocean, providing the first opportunity to analyze paleomagnetic variations and properties with depth. Unfortunately, each site probably sampled only a small number of flows, thus leaving the paleolatitude estimates open to considerable interpretation. Nevertheless, paleomagnetic latitudes at Sites 251, 253, 254, and 257 are compatible with reconstructions of the Indian Ocean based on lineated magnetic anomalies (McKenzie and Sclater, 1971; Sclater and Fisher, in press). Measurements of remanent magnetization were made on 67 samples (72 specimens) from Sites 250, 251, 253, 254, 256, and 257. Twenty-nine specimens were progressively demagnetized in alternating fields to less than 25% of their natural remanent magnetization (NRM) in1 Woods Hole Oceanographic Institution Contribution Number 2968. 7 Now at University of California, Santa Barbara, California. tensity, and a test for viscous remanent magnetization (VRM) was conducted using 20 specimens. Paleolatitude estimates, based on the geocentric dipole assumption, were made using the magnetic inclinations after cleaning in a peak alternating field of 100 oe. The following abbreviations for paleomagnetic terms are used in this report: AF, alternating field; G, Gauss (emu/cc); H100, AF demagnetized at 100 oe; Jnrm, intensity of NRM; MDF, median destructive field; NRM, natural remanent magnetization; oe, oersteds; S, magnetic viscosity coefficient; S/JnTm, normalized viscosity coefficient; SRM, shock remanent magnetization; Tc, Curie temperature; VGP, virtual geomagnetic pole; VRM, viscous remanent magnetization. NATURAL REMANENT MAGNETIZATION, COERCIVITY, AND SUSCEPTIBILITY Specimen magnetizations were measured on a spinner magnetometer with coil pickup (Phillips and Kuckes, 1967) operated at 9.5 Hz and 97.5 Hz. A Princeton Applied Research SM-2 spinner magnetometer, operated at 15 Hz, was used for a few oversize specimens. Intensities of NRM ranged from 3.9 × 10~ G to 4.33 ×10'G, the geometric mean for all samples being 3.22 × 10'G (Table 1). These values are comparable to those previously reported for DSDP basalts, but are somewhat lower than typical values for dredged basalts (Lowrie et al., 1973).

Paleomagnetic Results of Basalt Samples from DSDP Leg 26, Southern Indian Ocean