PROBING A POST-IMPACT HYDROTHERMAL SYSTEM IN THE CHICXULUB CRATER WITH CORE RECOVERED BY IODP-ICDP EXPEDITION 364

The Chicxulub impact event created a high-temperature anomaly in the crust of the Earth that produced a subsurface hydrothermal system that is a potential proxy for impact-related hydrothermal systems during the early evolution of thermophilic and hyperthermophilic life on Earth. A key objective of IODP-ICDP Expedition 364 was to drill into the peak ring of the crater to determine peak temperatures and the lifetime of the hydrothermal system. Analyses of the newly recovered core indicate Ca-Na- and K-metasomatism was prevalent at temperatures >300 °C, producing metasomatic fronts that moved through impact melt rocks and K-feldspar veins in the underlying granite. Relict quartz from the target entrained in the melt has been partially to wholly dissolved, implying a hot Si-undersaturated fluid, and the resulting void space later filled with secondary calcite. Deeper within the peak ring (1256 mbsf), the granite is honeycombed with quartz dissolution cavities that may be a consequence of that metasomatism at temperatures of 300 to 400 ºC. At 1313 mbsf, andradite garnet precipitated. Secondary muscovite cross-cuts shock-metamorphic kinking of feldspar and is probably of post-impact hydrothermal origin at temperature in excess of 350 ºC. The preservation of shock-produced TiO₂-II suggests that those temperatures are close to the maximum temperature. As the system cooled, Mg-Fe and Na-K sheet silicates precipitated. Melt fragments in the suevite are, for example, altered to saponite and montomorillonite-like smectite-group minerals with significant chemical zoning and variable nH2O. Lower temperature fillings of vugs and open cavities followed, producing surfaces covered with analcime, dachiardite, and other secondary minerals. The initially high temperatures would have sterilized local regions within the peak ring sequence. As the system cooled, it could have supported hyperthermophilic and thermophilic microorganisms for 10⁴ to 10⁵ years.