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Origin of the smooth zone in early Cretaceous North Atlantic magnetic anomalies
Author(s) -
Tominaga Masako,
Sager William W.
Publication year - 2010
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2009gl040984
Subject(s) - geology , magnetic anomaly , earth's magnetic field , crust , geophysics , oceanic crust , basalt , anomaly (physics) , polarity (international relations) , cretaceous , geomagnetic reversal , paleontology , magnetic field , subduction , physics , genetics , condensed matter physics , quantum mechanics , biology , cell , tectonics
Late Jurassic‐Early Cretaceous marine magnetic anomalies observed in the North Atlantic exhibit an abrupt change in character in M5‐M15 crust. The anomalies are smoother with low amplitudes, and are difficult to correlate among nearby profiles. The accepted explanation for the origin of this smooth zone is diminished resolution and anomaly interference due to slow spreading rates, which narrows the widths of polarity reversals in the crust and causes interference among sea‐surface anomalies. Magnetic modeling of these anomalies indicates that neither slow spreading rates alone nor slow spreading rates in combination with a decrease in geomagnetic field intensity can explain the basic character of the smooth zone. Combined with other geophysical evidence, our study suggests that one consequence of slow spreading rates that is responsible for the magnetic “smooth zone” is a thinned crustal basalt layer or a non‐basaltic magnetic source layer resulting from low melt supply during a period of ultra‐slow spreading.