Origin of the Pacific Jurassic quiet zone

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doi: 10.1130/G22894.1
Author(s): Tivey, Maurice A.; Sager, William W.; Lee, Sang-Mook; Tominaga, Masako
Author Affiliation(s): Primary:
Woods Hole Oceanographic Institution, Department of Geology and Geophysics, Woods Hole, MA, United States
Other:
Texas A&M University, United States
Seoul National University, South Korea
Volume Title: Geology (Boulder)
Source: Geology (Boulder), 34(9), p.789-792. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0091-7613 CODEN: GLGYBA
Note: In English. With GSA Data Repository Item 2006163. 24 refs.; illus., incl. sketch map
Summary: Understanding the marine magnetic anomaly record is critical for constructing realistic geodynamo models of global geomagnetic field, polarity reversal mechanisms, and long-term geomagnetic field behavior. One of the least understood portions of the marine magnetic anomaly record is also the oldest part of the record, the Jurassic quiet zone (JQZ), where anomalies become weak and difficult to correlate. The reason for the existence of the JQZ is unclear. It has been suggested that the JQZ is a true polarity superchron, similar to the Cretaceous normal superchron. Continental magnetostratigraphic studies have suggested that the JQZ is a period of rapid polarity reversal, of low field intensity, or both. We show results of a deep-tow survey of Pacific Jurassic crust that confirms the existence of magnetic anomalies within the JQZ. We tie Ocean Drilling Program Hole 801C (167.4 Ma) into the record and show that seafloor-spreading magnetic anomalies are present around the hole and extend to 170 Ma crust. We find a rise in reversal rate with increasing age with reversal rates over 10 rev/m.y. at 160 Ma and at 167 Ma. Anomaly amplitudes decrease in the record from 155 Ma until 162 Ma, where low-amplitude anomalies are difficult to correlate. Prior to 167 Ma, anomalies regain amplitude and remain strong until the end of our record at 170 Ma. The JQZ thus appears to be a combination of low-amplitude magnetic anomalies combined with rapid field fluctuations, which could be due to either intensity or polarity changes.
Year of Publication: 2006
Research Program: ODP Ocean Drilling Program
Key Words: 18 Geophysics, Solid-Earth; 20 Geophysics, Applied; Crust; Deep-tow methods; Geophysical methods; Geophysical surveys; Jurassic; Magnetic anomalies; Magnetic methods; Mesozoic; North Pacific; ODP Site 801; Ocean Drilling Program; Oceanic crust; Pacific Ocean; Paleomagnetism; Reversals; Surveys
Coordinates: N170000 N240000 E1580000 E1500000
N183831 N183835 E1562136 E1562134
Record ID: 2006071533
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States