Exploring the Magnetic Petrology of Ultramafic Rocks by 3D Modeling of Magnetic Anomalies
Abstract
Magnetic anomalies are observed on multiple scales, from the planetary to the submillimeter scale. Here we used 3D forward and inverse modeling of magnetic anomalies to gain insight into the rock and mineral properties of the magnetic sources, and the geometry of the bodies. Modeling is applied to two case studies and on two distinct scales.
In the first study ground and helicopter-borne magnetic data are used in combination with gravity data to explore the Reinfjord Ultramafic Complex (RUC) in Norway. The complex outcrops over an area of approximatively 12 km2. The magnetic anomalies do not match the mapped lithological boundaries, but are correlated with changes in magnetic properties and densities. Modeling of the geophysical anomalies indicates that the ultramafic complex has a minimum volume of 6.5 km3 and extends down to a minimum depth of 1400 m. Furthermore, at the northern side of the complex, the model explain the distinct magnetic anomaly low with a serpentinized area reaching a maximum depth of 400 m along one of the main faults crossing the complex. The second study investigates the magnetic anomalies at a submillimeter scale combining scanning magnetic microscopy with optical observations, scanning electron microscopy and electron microprobe analyses, rock magnetic methods, and magnetic modeling. Magnetic anomalies are measured over two thin sections from the RUC, a pristine dunite sample, and a serpentinized sample, each with distinct bulk magnetic properties. Forward and inverse modeling of the magnetic anomalies is used to characterize the natural remanent magnetization of discrete magnetic minerals within the samples in terms of intensities and direction. Modeling is made using the compositional and geometrical constraints given by optical and electron microscopy. The modeling results indicate heterogeneous sources of NRM within the grains with intensities varying from 2 to 14 A/m and variable directions. Modeling results confirm the microscopic observation and are consistent with the measured bulk magnetic properties. Magnetic anomalies were investigated on kilometer and submillimeter scales. Modeling of these anomalies in the two case studies resulted in different information on the magnetic petrology of the sources, and helped in refining the geological interpretation.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMDI43C0051P
- Keywords:
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- 3914 Electrical properties;
- MINERAL PHYSICSDE: 3619 Magma genesis and partial melting;
- MINERALOGY AND PETROLOGYDE: 5724 Interiors;
- PLANETARY SCIENCES: FLUID PLANETSDE: 8147 Planetary interiors;
- TECTONOPHYSICS