Linking Paleomagnetism and Petrographic Observations to Long-lived Hydrothermal Activity at the Chicxulub Crater

Hydrothermal systems are environments where nutrient-rich fluids may circulate within fractured and permeable rocks. During large cratering events, elevated temperatures are produced by the passage of the shock wave, the emplacement of impact melt, and the uplift of basement rocks. These heat sources may sustain hydrothermal systems for thousands to millions of years. Hydrothermal minerals are abundant within cores sampled during IODP-ICDP Expedition 364, indicating that a hydrothermal system was present in the Chicxulub impact crater. We conducted detailed petrographic microscopy and electron microprobe analyses of hydrothermally altered melt-bearing breccia (suevite) and impact melt rocks sampled during IODP-ICDP Expedition 364 to determine the occurrence of magnetic minerals within these lithologies. We found that visible (Ti-)magnetite grains are present in two locations: (1) within fractures and pore spaces of suevite and (2) isolated grains exsolved from impact melt glasses. We interpret these grains to be the product of hydrothermal mineralization and primary cooling of impact melt, respectively. Rock magnetic experiments including determinations of Curie temperatures and hysteresis properties indicate that the main remanence carrier in these lithologies is pseudo-single domain (Ti-) magnetite. The geomagnetic field exhibited reversed polarity at the time of impact (during chron 29r). However, our results indicate that the characteristic remanence components of the Chicxulub suevite included directions with both reversed and normal polarities. A combination of rock magnetic data, petrographic observations of hydrothermal (Ti-)magnetite, and statistical analyses suggest that the observed range in magnetization directions is unlikely to be entirely explained by rotated clasts within the suevite retaining pre-depositional remanence. Therefore, our paleomagnetic results suggest that Chicxulub impactites contain chemical remanent magnetization produced by long-lived hydrothermalism that extended into chron 29n, at least 240 kyr after the impact.