HR: 15:45h
AN: GP34A-02 INVITED     [Abstracts]
TI: Paleomagnetism from the Chicxulub Impact Crater: Past, Present and Prospectives
AU: * Rebolledo, M
EM: marior@cicy.mx
AF: Centro de Estudios del Agua, Centro de Investigaci¢n Cient¡fia de Yucat n, A.C., Calle 21 Nte., Lote 39 Manzana 26, S.M. 64, Canc£n, 77524 Mexico
AU: Urrutia, J
EM: juf@geofisica.unam.mx
AF: Instituto de Geof¡sica, UNAM, Ciudad Universitara Coyoac n, Mexico, DF 04310 Mexico
AU: Soler, A M
EM: anesoler@geofisica.unam.mx
AF: Instituto de Geof¡sica, UNAM, Ciudad Universitara Coyoac n, Mexico, DF 04310 Mexico
AB: Magnetic surveys over the Chicxulub Impact Crater had been carried out for the last 30 years, however it was until the Chicxulub Scientific Drilling Project started, that studies on the impact breccias and post-impact rock magnetic properties were performed. In this contribution, we report the results of our investigations on the magnetic properties from samples of breccia and post-impact lithologies recovered by Chicxulub Scientific Drilling Project, between 1996 and 2002. In general, NRM intensity and magnetic susceptibility present wide ranges, with values positively correlated, suggesting varying magnetic mineral contents and textures in the melt-rich breccias sequence. Vectorial composition and magnetic stability of NRM were investigated by stepwise alternating field and thermal demagnetization, which show characteristic magnetizations with linear components going through the origin of vector plots. NRM intensity ranges from 0.02 mA/m up to 37510 mA/m, suggesting varying magnetic mineral contents and textures in the melt-rich breccias sequence. Both upward and downward inclinations are observed, and we interpret the reverse magnetization as the primary component. The multivectorial composition of remanence may be related to the heterogeneous nature of the breccias and effects of hydrothermal activity. Clasts and matrix forming the breccias appear to have been subjected to a wide range of temperature/pressure conditions and show distinct rock-magnetic properties. We examined clasts of melt, granitic clasts and matrix from different intervals of breccias, to estimate grain-size and, along with thermomagnetic measurements, to identify the magnetic mineralogy. From the melt clasts we found "wasp-waisted" hysteresis cycles and we interpret the magnetic carrier as magnetite with a low content of titanium, with a low paramagnetic contribution and with grain-size within the range of pseudo-single domain. We found that the magnetic carrier in the granitic clasts is composed mainly of an iron mineral that present a strong paramagnetic component and grain-size within the multi-domain range.
DE: 1517 Magnetic anomaly modeling
DE: 1519 Magnetic mineralogy and petrology
DE: 1520 Magnetostratigraphy
DE: 1535 Reversals (process, timescale, magnetostratigraphy)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2005 Joint Assembly