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Early Central Atlantic Ocean seafloor spreading history

¹ Department of Geosciences, University of Houston, 4800 Calhoun Road, Houston, Texas 77204-5007, USA
² Department of Earth Science, Rice University, M.S. 126, 6100 South Main Street, Houston, Texas 77005-1892, USA

Twenty-three Mesozoic "Chrons" (specific time intervals) from M0 to M40, including several in the Jurassic Magnetic Quiet Zone ("Jurassic Quiet Zone"), as well as Cenozoic Chron C34, are identified and mapped between the Atlantis and Fifteen-Twenty fracture zones on the North American plate, and between the Atlantis and Kane fracture zones on the African plate. Asymmetric seafloor spreading is indicated by the distances spanned over Chron intervals for the western and eastern flanks of the Central Atlantic ocean basin: C34 to the Mid-Atlantic Ridge (84 Ma to 0 Ma), M0 to C34 (120.6 Ma to 84 Ma), and M25 to M0 (154 Ma to 120.6 Ma). Chron M40 (167.5 Ma) is mapped 65 km outboard of the S1 magnetic anomaly over the African flank, and its conjugate, the Blake Spur Magnetic Anomaly ("Blake Spur Anomaly") over the North American flank. Another pair of conjugate anomalies, the S3 magnetic anomaly over the African flank, and the East Coast Magnetic Anomaly ("East Coast Anomaly") over the North American flank, are respectively located 30 km and 180 km inboard of the S1-Blake Spur Magnetic Anomaly pair. Therefore, the ridge jump to the east between "Blake Spur" and "East Coast" anomalies at 170 Ma theorized by Vogt and others in 1971 is supported by this study. Between the Atlantis and Kane fracture zones, the width of the African Jurassic Magnetic Quiet Zone is 70 km greater (22%) than the North American Jurassic Magnetic Quiet Zone. Correlatable anomalies exist over the African plate, suggesting a second ridge jump, to the west. Modeling results indicate that this jump occurred between 164 Ma and 159 Ma (Chrons M38 and M32). The ridge jumps can be related to plate interactions as North America separated from Gondwana. However, we note that the second ridge jump occurred approximately at the time suggested for the onset of seafloor spreading in the Gulf of Mexico.

Keywords: Central Atlantic • ridge jumps • asymmetric spreading • seafloor spreading • magnetics • reconstruction