Related Experiment Video
Updated: Oct 19, 2025
07:42
Optimizing Magnetic Force Microscopy Resolution and Sensitivity to Visualize Nanoscale Magnetic Domains
Published on: July 20, 2022
2.9K
Three-dimensional magnetic stripes require slow cooling in fast-spread lower ocean crust
Sarah M Maher1, Jeffrey S Gee2, Michael J Cheadle3
1Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA, USA. s1maher@ucsd.edu.
Nature
|September 23, 2021
Summary
Earth's magnetic field records oceanic crust cooling. New findings show slow cooling and a broad, hot axial zone extending 8 km off-axis in fast-spread crust, challenging previous hydrothermal cooling models.
Area of Science:
- Geophysics
- Marine Geology
- Plate Tectonics
Background:
- Earth's magnetic field is imprinted on cooling oceanic crust, forming magnetic anomalies that reveal polarity reversals over 160 million years.
- Polarity boundaries in the lower gabbroic crust serve as isotherms, crucial for understanding crustal cooling and accretion processes.
- Existing seismic, geospeedometry, and thermal modeling studies of fast-spread crust offer conflicting views on heat loss mechanisms near mid-ocean ridges.
Purpose of the Study:
- To investigate the thermal structure and cooling processes within the lower crust of magmatically robust, fast-spread oceanic crust.
- To reconcile conflicting interpretations of heat loss and melt transport mechanisms near mid-ocean ridges.
- To refine models of oceanic crustal accretion and magnetic anomaly formation.
Main Methods:
- Analysis of magnetic anomalies using near-bottom magnetization solutions in two distinct areas.
- Paleomagnetic analysis of oriented rock samples to determine polarity components and cooling rates.
- Integration of magnetic data with existing seismic and thermal modeling constraints.
Main Results:
- Crustal temperatures near the dike-gabbro transition remain around 500°C for 0.1 million years.
- Subhorizontal polarity boundaries were identified within 200 meters of the dike-gabbro transition, extending 7-8 km off-axis.
- Direct evidence of slow cooling over three polarity intervals was found, confirming a broad, hot axial zone extending approximately 8 km off-axis.
Conclusions:
- The magnetic structure of fast-spread crust indicates slow cooling and a wide, hot axial zone, inconsistent with rapid hydrothermal cooling near the ridge axis.
- These findings suggest that heat is lost more gradually over a larger area in the lower crust of fast-spread oceanic settings.
- The study refines our understanding of melt transport, crystallization, and crustal accretion processes in active oceanic spreading centers.
More Related Videos
Related Concept Videos
01:23Atomic Nuclei: Nuclear Relaxation Processes
776
In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis, the precessing magnetic moments are randomly oriented around the z-axis.
776
01:19Magnetic Field Lines
4.6K
The representation of magnetic fields by magnetic field lines is very useful in visualizing the strength and direction of the magnetic field. Each of the magnetic field lines forms a closed loop. The field lines emerge from the north pole (N), loop around to the south pole (S), and continue through the bar magnet back to the north pole.
Magnetic field lines follow several hard-and-fast rules:
Magnetic field lines follow several hard-and-fast rules:
4.6K
01:28Magnetostatic Boundary Conditions
1.2K
An electric field suffers a discontinuity at a surface charge. Similarly, a magnetic field is discontinuous at a surface current. The perpendicular component of a magnetic field is continuous across the interface of two magnetic mediums. In contrast, its parallel component, perpendicular to the current, is discontinuous by the amount equal to the product of the vacuum permeability and the surface current. Like the scalar potential in electrostatics, the vector potential is also continuous...
1.2K
01:31Magnetic Susceptibility and Permeability
1.5K
In linear magnetic materials, like paramagnets and diamagnets, magnetization is proportional to the magnetic field intensity. The constant of proportionality, a dimensionless number, is called magnetic susceptibility. The value of the susceptibility depends on the type of material.
When diamagnetic materials are placed under an external magnetic field, the moments opposite to the field are induced. Hence, the susceptibility for diamagnets has a minimal negative value of 10-5–10-6. Since...
When diamagnetic materials are placed under an external magnetic field, the moments opposite to the field are induced. Hence, the susceptibility for diamagnets has a minimal negative value of 10-5–10-6. Since...
1.5K
01:26Divergence and Curl of Magnetic Field
3.3K
The magnetic field due to a volume current distribution given by the Biot–Savart Law can be expressed as follows:
3.3K
01:28Atomic Nuclei: Types of Nuclear Relaxation
456
Nuclear relaxation restores the equilibrium population imbalance and can occur via spin–lattice or spin–spin mechanisms, which are first-order exponential decay processes.
In spin–lattice or longitudinal relaxation, the excited spins exchange energy with the surrounding lattice as they return to the lower energy level. Among several mechanisms that contribute to spin–lattice relaxation, magnetic dipolar interactions are significant. Here, the excited nucleus transfers...
In spin–lattice or longitudinal relaxation, the excited spins exchange energy with the surrounding lattice as they return to the lower energy level. Among several mechanisms that contribute to spin–lattice relaxation, magnetic dipolar interactions are significant. Here, the excited nucleus transfers...
456