Paleomagnetically useful information is expected to be recorded by sampleswith moments up to three orders of magnitude below the detection limit ofstandard superconducting rock magnetometers. Such samples are now detectableusing recently developed magnetic microscopes, which map the magnetic fieldsabove room-temperature samples with unprecedented spatial resolutions and fieldsensitivities. However, realizing this potential requires the development oftechniques for retrieving sample moments from magnetic microscopy data. Withthis goal, we developed a technique for uniquely obtaining the net magneticmoment of geological samples from magnetic microscopy maps of unresolved ornearly unresolved magnetization. This technique is particularly powerful foranalyzing small, weakly magnetized samples such as meteoritic chondrules andterrestrial silicate crystals like zircons. We validated this technique byapplying it to field maps generated from synthetic sources and also to fieldmaps measured using a superconducting quantum interference device (SQUID)microscope above geological samples with moments down to 10^-15 Am2. For themost magnetic rock samples, the net moments estimated from the SQUID microscopedata are within error of independent moment measurements acquired using lowersensitivity standard rock magnetometers. In addition to its superior momentsensitivity, SQUID microscope net moment magnetometry also enables theidentification and isolation of magnetic contamination and background sources,which is critical for improving accuracy in paleomagnetic studies of weaklymagnetic rocks.
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