Insight into the post-impact hydrothermal system at the Chicxulub impact structure, Mexico
impact structures, Chicxulub crater, Mexico
The 66-million-year-old Chicxulub impact structure was formed by the hypervelocity impact of an asteroid into the Yucatán peninsula. Hypervelocity impacts generate hydrothermal circulation systems in the resulting craters and create long-term thermal anomalies in near-surface areas of the crust. Drill cores have sampled preserved impactites from the Chicxulub crater with the most recent core, M0077A, intersecting the peak ring. Analysis of the mineralogy, composition, and occurrence of secondary minerals in the core may be used to understand conditions in the postimpact hydrothermal environment. In this study, the secondary minerals within ten thin sections and five polished offcut tiles from drill core M0077A were investigated. The thin sections were sampled from ~750-1300 metres below sea floor (mbsf), while the tiles were constrained to a depth of ~1250-1330 mbsf. Identified secondary minerals include andradite-grossular garnet assemblages, anhydrite, Fe-oxides, calcite, Mg-Fe-Al-rich clay group minerals, sulfides, Casulphates, titanite, albite, fluorite, epidote, quartz, and halite. These minerals occur as vein- and vug-filling assemblages in the shocked granite and suevite breccia. The andradite-grossular garnet assemblages are of particular interest as they suggest that high-temperatures (300-400 C⁰) dominated the early stages of the post-impact hydrothermal system. Secondary minerals anhydrite, titanite, epidote, and Fe-oxides support the temperature range indicated by the garnets, but do not constrain the temperature as tightly. The temperature range indicated by the garnets is sufficiently hot for the hydrothermal system to persist for at least two million years, based on previous numerical modeling1,3. Calcite, Mg-Fe-Al-rich clay group minerals, sulfides, and halite formed as the hydrothermal system cooled. The secondary minerals identified attest to the depth and range of thermal and chemical modification that occurred in the Earth’s crust due to impact events, both immediately after and in the ensuing millions of years.
Groeneveld T. and Walton E. (2020) Insight into the post-impact hydrothermal system at the Chicxulub impact structure, Mexico. 2020 Geoconvention.
Presented on September 21-23, 2020 at the "GeoConvention 2020" virtual event.
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