The Fluctuation of the Geomagnetic-field Strength during the Cretaceous Quiet Zone: Paleointensity Results from Chinese Lavas

The geomagnetic field strength during polarity superchron is essential for understanding the geodynamo. Some numerical models suggest superchrons may represent periods when the pattern of core-mantle boundary heat flux allows geodynamo to operate at peak efficiency, but its validness needs to be tested. On the other hand, superchrons can provide us unique opportunities to unravel possible links between polarity reversal frequency, field strength, secular variation and geodynamo. However, paleointensity data from pre-Cenozoic time is scarce. In order to understand the field strength during the latest geomagnetic quiet zone, the Cretaceous Normal Superchron (CNS, 120-83 Ma), we conducted a series of full-vector paleomagnetic studies integrated with precise 40Ar/39Ar dating on the Cretaceous volcanic rocks collected from eastern China. Rather than a monotonously high or low intensity, we found that the field strength was relatively high but fluctuated. In combination with other available data, our observations suggest that the Earth’s deep interior was rather active then. Furthermore, paleointensities observed just prior to (and after) the CNS support that a positive relationship exists between the length of polarity interval and dipole moment.