1 / 12

Local inversion of Martian magnetic anomalies : geological implications

Local inversion of Martian magnetic anomalies : geological implications. Y . Quesnel, C . Sotin , B . Langlais and S. Le Mouélic Laboratoire de Planétologie et Géodynamique de Nantes (France). RST 2004 - Strasbourg , France 2 3/09/ 2004. One of the MGS MAG/ER results :

marianne-mercier
Download Presentation

Local inversion of Martian magnetic anomalies : geological implications

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Local inversion of Martian magnetic anomalies : geological implications Y. Quesnel, C. Sotin, B. Langlais and S. Le MouélicLaboratoire de Planétologie et Géodynamique de Nantes (France) RST 2004 - Strasbourg, France 23/09/2004

  2. One of the MGS MAG/ER results : A remanent field with strong magnetic crustalanomalies in the South Hemisphere (Acuña et al., 1999 ; Connerney et al., 2001) Question : Sources of these strong anomalies ? Methods : Local MGS MAG data simulation with uniformly magnetized spheres (Blakely, 1995) and prisms (Plouff, 1976) Generalized non-linear inversion (Tarantola and Valette, 1982) (Acuña et al., 1999) RST 2004 – Strasbourg, France Y. Quesnel, C. Sotin, B. Langlais and S. Le Mouélic – LPG Nantes (France) 23/09/2004

  3. Local MGS MAG Observations 0 200 km 0 200 km Bz AB data (80 < altitude < 250 km) Bz MO night data (altitude ~ 380 km) • Old crust • No correction of altitude : real data • ~10 times stronger than the Earth crustal anomalies for the same altitudes ! RST 2004 – Strasbourg, France Y. Quesnel, C. Sotin, B. Langlais and S. Le Mouélic – LPG Nantes (France) 23/09/2004

  4. Surface r m Latitude Longitude Depth Radius M Inclination Declination -32°N 191°E 60 km 60 km 45 A/m -45° 240° Model of uniformly magnetized sphere (Blakely, 1995) b Magnetic moment m = volume V * magnetization M Sphere <=> dipole RST 2004 – Strasbourg, France Y. Quesnel, C. Sotin, B. Langlais and S. Le Mouélic – LPG Nantes (France) 23/09/2004

  5. Model of uniformly magnetized prisms (Plouff, 1976) The « west prism » Area Thick Top depth Magnetization Inclination Declination 35600 km2 30 km 20 km 40 A/m -60° 180° Data Best model • All the prisms have a strong magnetization • This model fits well the MO night data too ! RST 2004 – Strasbourg, France Y. Quesnel, C. Sotin, B. Langlais and S. Le Mouélic – LPG Nantes (France) 23/09/2004

  6. Is Apollinaris Patera (-8°N, 174°E) a magnetic source ? Sphere Magnetized volume : 523 600 km3 Prisms Magnetized volume : 382 000 km3 AB < 150 km MO night data nT perturbation Models 200 km of altitude Data nT Sphere Both models are 1° southward the volcano center location. This simulation shows that Apollinaris Patera is a magnetic source. Prisms

  7. Generalized non-linear inversion with a least-square criterion (Tarantola and Valette, 1982) Input : MGS data + a priori parameters of dipoles (location, depth Z, dipolar moment m, inclination I and declination D) Output : best parameters of dipoles 185°E 190 200 210°E -26°N I = -46° Z = 93 km m = 7,8.1016 A.m2 -30 I = -79° Z = 41 km m = 2,8.1016 A.m2 I < 0 I = 31° Z = 86 km m = 8,5.1016 A.m2 I > 0 -35 I = -62° Z = 47 km m = 1,5.1016 A.m2 I = -9° Z = 74 km m = 2,1.1016 A.m2 -40°N 0 200 km RST 2004 – Strasbourg, France Y. Quesnel, C. Sotin, B. Langlais and S. Le Mouélic – LPG Nantes (France) 23/09/2004

  8. First conclusions • Good simulation with strongly magnetized material • No coherence between dipoles after inversion • No correlation with craters Iron-bearing minerals : magnetite, hematite, pyrrhotite, or pure iron Which material ? Volcanism, plutonism, hydration, or weathering Which process ? RST 2004 – Strasbourg, France Y. Quesnel, C. Sotin, B. Langlais and S. Le Mouélic – LPG Nantes (France) 23/09/2004

  9. 30 (Mg0.8 ; Fe0.2) SiO3 + 18 H2O 8 Mg3Si2O5(OH)4 + 2 Fe3O4 + 2 H2 + 14 SiO2 Enstatite (20 % Fe) Water Lizardite Magnetite Dihydrogen Quartz Geological model : serpentinization Assumptions : - hydrated crust - mantle convection - Earth-like dynamo A 40 A/m magnetization is compatible with a 10 % mass-fraction of magnetite corresponding to a 8 % hydration. RST 2004 – Strasbourg, France Y. Quesnel, C. Sotin, B. Langlais and S. Le Mouélic – LPG Nantes (France) 23/09/2004

  10. Perspectives Contribution of the Mars Express OMEGA imaging spectrometer data : comparison with terrestrial spectra of olivine, pyroxene, serpentine and magnetite (example of the Ronda massif : Launeau et al., 2002) (S. Le Mouélic, personal communication, 2004) Mineralogical composition of Mars surface and below (crater ejecta…) RST 2004 – Strasbourg, France Y. Quesnel, C. Sotin, B. Langlais and S. Le Mouélic – LPG Nantes (France) 23/09/2004

  11. Mars Express Cover up until now (S. Le Mouélic, personal communication, 2004)

  12. Acknowledgments This work benefited from the support of the European Community’s Improving Human Potential Programme under contract RTN2-2001-00414, MAGE.

More Related