An Investigation of Small Scale Ridge Axis Offsets Using Near Bottom Magnetic Data from the East Pacific Rise, 9° 25'N to 9° 58'N
Abstract
The axial high of the fast-spreading East Pacific Rise (EPR) mid-ocean ridge (MOR) is known to be offset over multiple length scales. Devals (deviations from axial linearity) are the smallest defined offsets (<0.5km) separating the ridge into 5-15km length segments which, it has been suggested, form as a consequence of distinct magmatic systems distributed along the spreading axis. High-resolution magnetic field data provides information on how stable and long-lived these "devals" are through time and whether or not they migrate like the larger scale offsets. Previous magnetic surveys along the segment of the EPR between 9° -10° N have identified the Central Anomaly Magnetic High (CAMH) along the ridge axis, which is believed to reflect both the width of the neovolcanic zone and the spatial distribution of lava emplacement. However, interpretation of the CAMH has remained ambiguous because of the low resolution of these sea surface level data. We present the analysis of near bottom magnetic data ( ∼100m above the seafloor) collected between 9° 25'N and 9° 58'N. Our main goal is to identify any offsets or variations in magnitude of the magnetic anomaly and magnetization results that may correlate with observed "deval" offsets in the topography from detailed side scan images. Crustal magnetization represents a time-integrated signal so that any observed magnetic offsets would indicate that these offsets have been stable on timescales of a few thousands to tens of thousands of years. First, we find undulations in magnetization amplitude along ridge axis with "lows" located at "deval" offsets. However, there are no significant lateral offsets in the magnetization suggesting that "devals" are ephemeral features. Second, from the south to the north in the study area we see a first order increase in magnetisation around 9° 37'N. Possible reasons for this increase include thickening of the axial crust, a systematic change in geochemistry or recent extrusion of lavas. Finally, it is known that Layer 2a thickness doubles over 1-2km distance away from the ridge axis. This has been attributed to off axis deposition of lavas and the character of the CAMH is influenced by these features. Several finger like anomalies which run from the axis out onto the flanks appear to correlate with these lava flows.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2003
- Bibcode:
- 2003AGUFM.B12A0737W
- Keywords:
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- 1550 Spatial variations attributed to seafloor spreading (3005);
- 3035 Midocean ridge processes;
- 3045 Seafloor morphology and bottom photography;
- 8429 Lava rheology and morphology;
- 9355 Pacific Ocean