Magnetic signature of all Martian meteorites (SNC)
Final Report Abstract
The complexity of the magnetic record and magnetic signature of the Martian meteorites justifies well in our opinion that we decided to extend the project frame significantly by several topics, as mentioned above. Currently we are far away from a satisfying understanding of the Mars magnetism, Mars crustal anomalies, missing impact site anomalies, and even more further away from a substantiated argumentation basis concerning a (likely or non likely) early Mars dynamo field. So far, the only “old” Martian rock in our hands was believed to be ALH84001 (> 4Gyrs), however new results doubt the apparent young ages of many shergottites. Recent re- or more detailed studies gave much higher formation ages, around and above 4 Gyrs, and the shergottite age debate is ongoing. Eventually the young shergottite formation ages may only represent shock or alteration ages and not real formation ages. Neither we have any “ground-based” knowledge concerning the “magnetic age” and the physical background of the strong crustal anomalies, nor about the responsible magnetic mineralogy, phases and recording processes on Mars. According to our results, the magnetic signature of impactites (or generally impact modified rock formations), covering large parts/volumes of the Mars surface, eventually in quite thick layers and formations, might play a very important role with respect to the magnetic anomaly physical and petrological background. The question arises whether most or even all currently known magnetic features on the Mars surface and in Martian meteorites are impact related? From laboratory shock investigations we know very well that strong magnetization effects/records can be obtained in (geo-)materials by shock metamorphic processes (impact-like) even in zero magnetic field which could be shown by a variety of zero field experiments. Only future missions to Mars could substantially help to solve these problem if lander/rover experiments would be foreseen in the Noachian Highlands (eg MAVEN mission). One can transfer this problem circle to the Earth Moon, challenging the former hypothesis of an ancient Moon dynamo field, which is based on paleointensity data being currently under heavy discussion again. In this case, we don’t have any knowledge from lunar meteorites. Only one lunar meteorite was studied so far by my colleague M. Funaki (NIPR) and the data compared with lunar highland anorthosite results from the Apollo mission. (i) All investigated Martian meteorites (MM) are able to carry a strong and reliable (paleo)magnetic signal. However, only a certain number of Mars rocks do obviously carry a stable and reliable magnetic remanence of Martian origin. (ii) The role and meaning of shock on the magnetic record of the MM was underestimated in generally. For example, even so petrological features point to only low shock of about 20 GPa or less, Nakhlites magnetic signature points to much higher shock degrees, at least locally. We believe this fact most likely being a consequence of the differences in rheological properties of the various mineral phases of the MM. A certain shock degree determined on silicate phases (and in most cases used for the shock classification of the whole rock) might not be a representative measure for shock effects in oxide or sulfide phases which are the recorders of the (paleo)magnetic signal. (iii) Shock neoformation of strongly magnetic phases of native Fe-Ni or magnetite in lherzolitic shergottites, shocked dunite and some ol-opx phyric shergottites seems to be a common process on Mars surface impactite rocks. The role of these phases for the magnetic anomalies of the Mars crust and the paleomagnetic record in generally is presently unclear. A major contribution can be expected because large parts of Mars surface are covered by thick layers of impactite rocks and formations. (iv) Presently we assume that the paleomagnetic record of the Martian meteorites is mainly related to impact events. Sometimes multiple shocks are known, at least to the last impact which finally ejected the Mars rocks into space. (v) Main magnetic phases in MM are low Ti titanomagnetite and magnetite, pyrrhotite, pentlandite, at low T (space conditions) also chromites of various compositions and ilmenite might play a role as remanence carriers. (vi) Terrestrial alteration effects play a very important role concerning the magnetic signature and record, specifically in case of the nano phase bearing MM. (vii) Generally, the magnetic record of MM is very complex and as a next step, after having established the MM magnetic signature database, we need to identify the role of the individual magnetic records and recorders and the various processes which are behind these records (formation, single-multi-impact, alteration, ...). (viii) A better and detailed understanding of these records and processes requires setting up a large series of laboratory experiments on terrestrial equivalents, rocks and mineral phases. (ix) Also, new and highly sophisticated high resolution techniques have been tested and applied within this project for the above mentioned purposes: a number of micromagnetic experiments including MFM, Magnetotactic Bacteria for mapping the magnetic vectors on shocked olivines in lherzolites, and recently Magneto Impedance Microscopy, testing the meaning of magnetic record of individual magnetic grains and recorders. (x) Recently, a number of new and fascinating Martian meteorites have been found and published. Consequently our project results and database represent a starting point and we must include recent and future findings subsequently in our investigations. Follow up projects jointly with our colleagues from Japan within our approved co-operations are currently in the state of initiation and planing.
Publications
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A synthesis on the magnetic properties of Martian meteorites. LPSC 2005, #1614, League City
Rochette P., Gattacceca J., Chevrier V., Hoffmann V., Lorand J.P., Funaki M., Hochleitner R
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Matching Martian crustal magnetization and meteorite magnetic properties. Meteor. Planet. Science, 40/4 (2005), 529-540
Rochette P., Gattacceca J., Chevrier V., Hoffmann V., Lorand J.P., Funaki M., Hochleitner R.
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Comparative magnetic signature of Martian meteorites Yamato 000593, Yamato 000802, Yamato 000749, Yamato 980459 and ALH 77005. Antarctic Meteor. XXX (2006), 22-23, Tokyo. (NIPR International Conference Antarctic Meteorites, 2006)
Hoffmann V., Funaki M.
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Yamato 000097 magnetic signature and comparison with other lherzolitic shergottites. Antarctic Meteor. XXXI (2007), 26-27, Tokyo. (NIPR International Conference Antarctic Meteorites, 2007)
Hoffmann V., Funaki M., Torii M.
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Magnetic signature of lherzolitic shergottites ALH77005 and Yamato 000097: “brown” colour olivines and detection of the Fe metal particles by magnetotactic bacteria. LPSC 2008, #1703, League City
Hoffmann V., Funaki M., Torii M., Kurihara T., Mikouchi T.
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Transmission electron microscopy of “Brown” colour olivines in Martian and Lunar Meteorites. LPSC 2008, #2478, League City
Kurihara T., Mikouchi T., Saruwatari K., Kameda J., Arai T., Hoffmann V., Miyamoto M.
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Estimate of the magnetic field of Mars based on the magnetic characteristics of the Yamato 000593 nakhlite. Meteor. Planet. Science, 44/8 (2009), 1179-1191
Funaki M., Hoffmann V., Imae N.
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Magnetic signature of experimentally shocked San Carlos olivines: simulation of the neoformation processes of nanosized Fe-Ni and magnetite particles in brown coloured olivines of some Martian meteorites. LPSC 2009, #2194, Houston
Hoffmann V., Mikouchi T., Kurihara T., Funaki M., Torii M.
