Mars MOURA magnetometer demonstration for high resolution mapping on terrestrial analogues

摘要

Satellite-basedmagnetic measurements of Mars indicate complex and very strong magnetic anomalies,which led to an intensive and long-lasting discussion abouttheirpossible origin. To investigate the origin of these anomalies MOURA vector magnetometer was developedforfuture on ground surveyson Mars andtested on various terrestrial analogues characterised by most distinct magnetic anomaliesof theirbasement rocks: (1) Amagnetite body of EL Laco (up to +110 000 nT) and its transition to surrounding andesites (< +2000 nT)in the Northern Andes of Chile showing the highest local magnetic anomalies. The magnetite-bearingore bodyhashighly variablelocal anomaliesdue to their complex formation history where a significantdispersion inpaleo-orientations has been previously reported, while our vector data show relatively uniform and probably induced declinations. (2) Abasaltic spatter cone ofthe Pali Aike volcanic field, in Southern Chile,was characterised by very strong magnetic anomalies along thecrater rim(up to +12 000 nT),controlledby the amount of single domain magnetites in the ground mass of the basalts.Due to their strong remanent signature paleodeclinations of the lavasand reorientationsofcollapsedblocks couldbe constrained by the vector data. (3) The Monturaqui meteorite crater (350 m diameter), in Northern Chile,showssignificant variations of its anomalies (from −2000 to > +6000 nT) in restricted areas of several square metres along itscrater rim related tounexposediron-bearing fragmentsof the impactorwhile itsgranitic and ignimbritictarget rocks exhibit only very weak anomalies.(4) An area with several amphibolitic dykes which cross-cut a Cretaceous granitoid in the southernmost Andes, wherea decimetre-scale mapping was performed. In this case, pyrrhotite is theonly magnetic carrier. It wasformed during hydrothermal processeswithin the dykes. Very low (+40 to +120 nT) positive magnetic anomalies clearly depict the amount of1 to 4 vol. %pyrrhotite in thesedykes,which is importantas a mineralogical indicator as well asto detect associated gold and copper enrichment.