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The Origin of the Jurassic Quiet Zone: new insights from Hawaiian Jurassic magnetic anomalies

Control ID: 1783103

Title: The Origin of the Jurassic Quiet Zone –new insights from Hawaiian Jurassic magnetic anomalies (Invited)

Authors (First Name, Last Name): Masako Tominaga1, 2, Maurice Tivey2, William W Sager3

Institutions (All):

  1. Geological Sciences, Michigan State University, East Lansing, MI, United States.
  2. Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA, United States.
  3. Earth and Atmospheric Sciences, University of Houston, Houston, TX, United States.

Abstract Body: Marine magnetic anomalies recorded in oceanic crust, have played a central role in documenting Earth's magnetic field history as compiled in the geomagnetic polarity timescale (GPTS). The oldest part of the marine record is the Jurassic Quiet Zone (JQZ) (pre-M29 chrons) which is known to be a period when field intensity was low, while reversal rate was high. The origin and character of the JQZ has been the subject of marine magnetic studies over past 20 years in the western Pacific where the oldest and arguably best preserved Jurassic magnetic anomalies create three Jurassic lineation sets (Japanese, Hawaiian, and Phoenix). The Japanese JQZ sequence was extensively investigated by an aeromagnetic and 2 deeptow magnetometer surveys, revealing (i) the presence of lineated anomalies older than M29; (ii) a GPTS record extending from M29 to M44 with a tie to ODP Hole 801C and (iii) remarkably fast reversals that decrease in intensity back in time until M38. Prior to M38 there is a low amplitude zone (LAZ) in anomalies lasting until M42, when both anomaly amplitude and a lineated character reappears around Hole 801C. Recently collected (2011) high quality seasurface marine magnetic anomaly data from the Hawaiian lineations show changes in magnetic anomaly shape and amplitude that are similar in to the Japanese lineations, suggesting that the anomalies record globally coherent geomagnetic field behavior for the Jurassic. Specifically, the strong similarity of anomaly patterns between the Japanese and Hawaiian sequences from M19 to M38 supports the remarkably dynamic geomagnetic field behavior of fast reversals and changing intensity, confirming a proposed record of the GPTS sequence for M29 to M38. While the LAZ in the Hawaiian sequence is not as clear as in the Japanese lineations, we believe we can correlate the earlier M42-M44 sequence between the two sets of lineations. The slower spreading rate in the Hawaiian lineations may contribute to this lack of resolution of the LAZ and result in a less clear recording of anomalies. We present models to investigate if this is simply a lack of spatial resolution or if there are indeed different processes active within the Hawaiian sequence such as seamount/plateau formation and crustal construction.

Keywords: 1517 GEOMAGNETISM AND PALEOMAGNETISM Magnetic anomalies: modeling and interpretation, 3005 MARINE GEOLOGY AND GEOPHYSICS Marine magnetics and paleomagnetics, 3000 MARINE GEOLOGY AND GEOPHYSICS.