James R. Heirtzler

Magnetic Anomalies over the Pacific-Antarctic Ridge

Four magnetic profiles across the Pacific-Antarctic Ridge reveal magnetic anomalies that show trends parallel with the ridge axis and symmetry about the ridge axis. The distribution of bodies that could cause these anomalies supports the Vine and Matthews hypothesis for the generation of patterns of magnetic anomalies associated with the midocean ridge system. The geometry of the bodies accords with the known reversals of the geomagnetic field during the last 3.4 million years, indicating a spreading rate of the ocean floor of 4.5 centimeters per year. If one assume that the spreading rate within 500 kilometers of the ridge axis has been constant, reversals of the geomagnetic field during the last 10.0 million years can be determined. This new, detailed history of field reversals accords with observed anomalies over Reykjanes Ridge in the North Atlantic if a spreading rate of 1 centimeter per year is assumed there.

Magnetic boundaries in the north atlantic ocean.

Magnetic boundaries parallel the continental slope and separate undisturbed from disturbed magnetic regions on both sides of the North Atlantic. The boundaries lie 2000 to 2500 kilometers from the axis of the mid-Atlantic ridge and roughly equidistant from it. The undisturbed zone, lying on the continental side of the boundaries, may reflect the long period of no reversals in magnetic polarity that occurred during the late Paleozoic.

Sea-Floor Spreading near the Galapagos

Seismicity, volcanism, and a linear pattern of very large magnetic anomalies that show symmetry about a broad negative anomaly suggest that a type of sea-floor spreading occurs near the Galapagos Islands in the east-equatorial Pacific. This spreading results from the tensile stresses generated by different spreading directions of two adjacent segments of the East Pacific Rise, and it is suggested that the area be called the Galapagos Rift Zone.

Magnetic anomalies over the Reykjanes Ridge

Abstract A detailed aeromagnetic survey has been made over a large portion of the Reykjanes Ridge. The magnetic pattern observed displays great linearity, parallel to the topographic trend of the ridge and has the topographic crest as an axis of symmetry. The identification of two main magnetic provinces, noted in previous studies of the mid-ocean ridges, is confirmed. Possible relations between the structures of the Icelandic Plateau and the Reykjanes Ridge were investigated.

Sub-bottom Study of Long Island Sound

Seismic reflection and magnetic measurements made over the last ten years in Long Island Sound have been combined with earlier seismic refraction data and with geological data on the surrounding land to provide details of the Pleistocene history of the area. Long Island Sound is at present shallow and the bottom is of low relief. Reflection data indicate the presence of relief on the order of many hundreds of feet beneath the bottom. The combined geophysical data indicate that the relief is in the primarily Cretaceous cover over the basement in the Sound and is related to the Pleistocene glaciation of the area. This conclusion is supported by correlations with surface geology and physiography and with data from boreholes. The magnetic measurements can be interpreted to support the suggestion of Sanders (1963) that the Triassic of Connecticut extends beneath the Sound at least as far as the north shore of Long Island.

Magnetic measurements near the deep ocean floor

Abstract During the period 11 to 14 June 1963, while searching for the sunken submarine Thresher in the Northwest Atlantic, a proton precession magnetometer was towed 20 m above the ocean floor. A total intensity contour map of a small area of the bottom reveals a geological anomaly of approximately 25 gammas amplitude and approximately 2 km in extent. When away from this anomaly the field strength increases wuth depth as appropriate for a geomagnetic dipole. Near the anomaly the field strength increases with depth at a rate greater than that appropriate for a geomagnetic dipole. Time variations in total magnetic intensity on the ocean floor appear to follow closely time variations of the horizontal component of field strength on land.