Paleomagnetic and Rock-Magnetic Study of the Yaxcopoil-1 Impact Breccia Sequence, Chicxulub Impact Crater (Mexico)

Results of a detailed paleomagnetic and rock-magnetic study of samples of the impact breccia sequence cored in the Yaxcopoil-1 borehole between about 800 m and 896 m are presented. The Yaxcopoil-1 breccia sequence occurs from 794.63 m to 894.94 m and consists of relatively complex melt-rich suevites. The low-field susceptibility ranges from -0.3 to 4018 10-5 SI. The NRM intensity ranges from 0.02 mA/m up to 37510 mA/m. In general, NRM intensity and magnetic susceptibility present wide ranges and their values are positively correlated, pointing to varying magnetic mineral contents and textures of the melt-rich breccia sequence. The vectorial composition and magnetic stability of NRM were investigated by both stepwise alternating field and thermal demagnetization. In most cases characteristic magnetizations with linear components going through the origin of vector plot are observed. Both upward and downward inclinations are observed in the breccia samples. We interpret the reverse magnetization as the primary component. The multivectorial composition of remanence may be explained by the heterogeneous nature of the breccias and effects of hydrothermal activity. Clasts and matrix forming the breccia appear to have been subjected to a wide range of temperature/pressure conditions and show distinct rock-magnetic properties. High temperature/pressure conditions during cratering resulted in melting, formation of metamorphic minerals, generation of shock features in quartz and plagioclases, crustal uplift, widespread fracturing and deformation and generation of a thermal anomaly. An extended interval of remanence acquisition and secondary partial or total remagnetization may explain the paleomagnetic results.