HR: 1340h
AN: GP43B-0856    [Abstracts]
TI: Deep-tow Study of Magnetic Anomalies in the Pacific Jurassic Quiet Zone
AU: * Tominaga, M
EM: mtominaga@ocean.tamu.edu
AF: Department of Oceanography, Texas A&M University, College Station, TX 77843 United States
AU: Sager, W W
EM: wsager@ocean.tamu.edu
AF: Department of Oceanography, Texas A&M University, College Station, TX 77843 United States
AU: Tivey, M A
EM: mtivey@whoi.edu
AF: Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543 United States
AB: The Jurassic Quiet Zone (JQZ) is a region of low-amplitude, short-wavelength, difficult-to-correlate magnetic anomalies located on Jurassic seafloor and thought to represent a time of decreased field strength and rapid reversals. We collected new deep-tow magnetic data over the Pacific JQZ that complement 2 deep-tow profiles reported in Sager et al. (J. Geophys. Res., vol.103, p. 5269, 1998). Our primary goals were to extend the correlation of deep-tow magnetic anomalies farther back in time, crossing ODP Site 801 (where Jurassic ocean crust has been drilled and cored), to evaluate the correlation of anomalies, and to refine the Jurassic geomagnetic polarity reversal time scale developed by Sager et al. (1998). These new data include: (1) closely spaced lines around M34 and Site 801, (2) two long lines extending from the previous survey, across Site 801 to the southeast, and (3) one line between the previous lines in the area of difficult-to-correlate anomalies. Systematic changes in anomaly amplitudes occur along the deep-tow lines, perhaps indicating changes in field strength. From northwest to southeast (i.e., increasing in age) anomaly amplitudes and wavelengths decrease, become nearly constant, and then increase slightly. The zone of smallest, shortest wavelength anomalies corresponds to a period of ~4 m.y. that appears to have an abrupt end. Comparing anomalies between lines, correlations were excellent on the closely-spaced profiles over M34 and around Hole 801C. Correlation over supposedly older seafloor to the south of Site 801 was also good. However, anomaly correlation in the region between M34 and Site 801 was difficult. As with other studies of magnetic profiles, it is impossible to uniquely determine which anomalies are caused by reversals and which are not. Many of the larger anomalies are likely caused by changes in polarity, whereas smaller anomalies may be intensity fluctuations. The new deep-tow data, being closer to the source than the previous lines, show more short-wavelength anomalies in some areas, particularly the area where anomaly amplitudes are least. This observation suggests that many of these short-wavelength anomalies may result from intensity fluctuations. To construct a reversal time scale, we limit short wavelengths by modeling magnetic profiles upward continued to mid-water depth.
DE: 3005 Geomagnetism (1550)
DE: 1517 Magnetic anomaly modeling
DE: 1521 Paleointensity
DE: 1535 Reversals (process, timescale, magnetostratigraphy)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting