Magnetic modeling of the sea floor: Analysis of short wavelength variations within the Brunhes and anomaly 5 normal polarity intervals

Near-bottom magnetic surveys performed over both 10 million year old oceanic crust of anomaly 5 and crust accreted within the last 800 kyr at the Cleft segment of the Juan de Fuca ridge (JDFR) in the NE Pacific indicate that paleomagnetic field variations are recorded within oceanic crust. Anomaly 5 data indicated a more strongly correlated pattern of linear, short-wavelength (2 to 5 km) anomalies than was observed within the slightly slower spreading Brunhes magnetic anomaly data at the JDFR. However, both the occurrence of the central anomaly magnetic high and an abrupt decrease in paleointensity around 300 Ka, two features which globally occur within the Brunhes, in each of the magnetization profiles indicate that fluctuations of the geomagnetic field are being recorded within the crust at the JDFR. Calculation of the transition zone widths at known reversals indicates that the NE Pacific anomaly 5 data is of higher resolution with a shorter mean transition zone width and less variance than the slower spreading JDFR data. Further comparison of anomaly 5 data collected in the NE Pacific and near bottom magnetic anomaly data collected over oceanic crust generated at the much faster spreading East Pacific Rise shows a remarkable similarity between the two data sets. A similar comparison between stacked magnetization profiles of the JDFR and EPR data indicates very little correlation. Comparison between the JDFR and EPR magnetization stacks and paleointensity data derived from sediment cores shows no correlation between the JDFR and sediment core data, whereas a correlation at wavelengths greater than 42 kyr is observed between the EPR and sediment paleointensity records. The lower resolution observed across and along axis at slower spreading centers is attributed to: (1) the overlapping of young lava flows onto and the intrusion of dikes into crust with a greater age range than present within a comparable distance of the ridge axis at faster spreading centers, and (2) the more temporally and spatially episodic magma supply characteristic of slower spreading centers.