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IAGA 2005 - Toulouse , France 2 2/07/ 2005

Inversion of Terrestrial and Martian magnetic anomalies: geological implications. Y. Quesnel (1), B. Langlais (1), S. Le Mouélic (1), C. Sotin (1) and A. Galdéano (2)

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IAGA 2005 - Toulouse , France 2 2/07/ 2005

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  1. Inversion of Terrestrial and Martian magnetic anomalies: geological implications Y. Quesnel (1), B. Langlais (1), S. Le Mouélic (1), C. Sotin (1) and A. Galdéano (2) (1) Laboratoire de Planétologie et Géodynamique de Nantes, UMR-CNRS 6112 (2) Géomagnétisme Interne, IPG Paris, UMR-CNRS 7577 IAGA 2005 - Toulouse, France 22/07/2005

  2. Crustal magnetic anomalies ↔ Crustal sources ? Correlation between magnetic anomaly and geological maps (near-surface investigation…) Crustal sources Forward models (geometry, magnetization) Inversion (depth, orientation) Modeling methods IAGA 2005 - Toulouse, France 22/07/2005

  3. Outline • Modeling method • Application to Martian magnetic satellite data • Application to Terrestrial aeromagnetic data • Geological implications • Future work IAGA 2005 - Toulouse, France 22/07/2005

  4. Method Forward models: uniformly magnetized spheres (Blakely, 1996) and prisms (Plouff, 1976) Generalized non-linear inversion (Tarantola and Valette, 1982): • Data: Bx, By, Bz • Parameters: mx, my, mz, x, y, z (moment and location of one or several dipoles) • Equations: three components of the magnetic field created by a sphere • Iterative process: minimum chi-squared criterion • Final test: data misfits, gaussian distribution IAGA 2005 - Toulouse, France 22/07/2005

  5. A remanent field ! AB (Br) MO(Br) (Acuña et al., 1999) Area: ancient southern highlands of Terra Sirenum Type of data: three vector components AB (100-250 km) and MO (400 km) MGS MAG/ER measurements Application to Martian satellite data IAGA 2005 - Toulouse, France 22/07/2005

  6. Application to Martian satellite data AB (100-250 km) MO (400 km) Data Results of three different data set tests: (input dipole location parameters from forward modeling studies) IAGA 2005 - Toulouse, France 22/07/2005

  7. Application to Martian satellite data AB (100-250 km) MO (400 km) Data Model (3 dipoles) 1 1 3 3 2 2 IAGA 2005 - Toulouse, France 22/07/2005

  8. I Nantes Nantes Application to Terrestrial aeromagnetic data Area: the Armorican Massif (France) Type of data: total magnetic field airborne measurements at 120 m above topography (summer 1998 ; BRGM) Geological setting IAGA 2005 - Toulouse, France 22/07/2005

  9. 1 2 3 3 prisms model: Application to Terrestrial aeromagnetic data N Forward modeling (first results): 1 2 3 3 spheres model: IAGA 2005 - Toulouse, France 22/07/2005

  10. 11 A/m 3 A/m Geological implications The Armor2 seismic profile from Bitri et al., C.R. Geosciences, 335, 2003: S N 0 5 10 15 20 25 30 35 Depth (km) IAGA 2005 - Toulouse, France 22/07/2005

  11. Alteration of forsterite (10% Fe) with water: 30Fo90 + 41H2O  15Lizardite + 2Fe3O4 + 9Mg(OH)2 + 2H2 Serpentinization model (early Mars) Geological implications Results of the Martian investigation: - no correlation between adjacent sources - no links with craters in the studied area - strongly magnetized materials → magnetite ? how ? IAGA 2005 - Toulouse, France 22/07/2005

  12. Future work… • Inversion of terrestrial aeromagnetic data • Terrestrial satellite measurements investigation • Study of other areas on Mars • Correlation with surface mineralogy : OMEGA Mars Express Comparison with terrestrial spectra of olivine, pyroxene, serpentine and magnetite (example of the Ronda massif: Launeau et al., 2002) IAGA 2005 - Toulouse, France 22/07/2005

  13. Acknowledgments This work benefited from the support of the European Community’s Improving Human Potential Programme under contract RTN2-2001-00414, MAGE. IAGA 2005 - Toulouse, France 22/07/2005

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