Mathematics – Logic
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmgp11b0081n&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #GP11B-0081
Mathematics
Logic
1540 Rock And Mineral Magnetism, 1595 Planetary Magnetism: All Frequencies And Wavelengths
Scientific paper
(De)mangetization by strong stress waves is thought to be responsible for magnetic anomalies observed over some impact craters, e.g. those on Martian and lunar surfaces. Stability of remanence against stress waves is not fully understood although its better understanding may lead to stronger constraints on conditions where a crater is formed (strength of pressure, physical properties of magnetic minerals, presence or absence of external field, etc). In this context, we are carrying out rock magnetic investigations of Lonar impact crater formed on Deccan basalts. The crater is an appropriate target of the study for the reasons of its strong magnetization, the relatively simple geological structures and the young formation age (< 50,000 yrs). Basalt samples were collected from total 21 sites on the inner walls and also out side of the rim that is expected to have been less shocked. Two remanence components were isolated by stepwise alternating field demagnetization (AFD). The paleomagnetic directions were corrected for the tilting due to the raised rim. As a result, we observed no evidence of shock remanence. The higher coercivity component is the pre-impact magnetization since they passes fold test, and the mean directions after the tilt correction cannot be distinguished from that for the outer crater sites. The higher components for the inner-wall sites may have been partially demagnetized by the shock. Their NRM intensity normalized by anhysteretic remanence is generally smaller for the inner wall sites, especially for those at low altitude. They also show relatively linear NRM decay curves during the AFD, which infers that the low coercivity parts were preferentially demagnetized. We also report the preliminary result of ground magnetic survey out side the craters. We used small magnetometer systems originally developed for use with the unmanned aerial vehicles. The results showed that short wavelength anomalies seem to be present, which may be result from shock demagnetization.
Funaki Minoru
Nishioka I.
Rao Vittal
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