The Chicxulub Impact Structure Reveals the First In-Situ Jurassic-Aged Magmatic Intrusions of the Yucatán Peninsula, Mexico
28 Pages Posted: 17 Jun 2022
Large impact events excavate mid- to lower-crustal rocks, offering a unique perspective on the interior composition and tectonic history (if any) of planetary bodies. On the Yucatán Peninsula, Mexico, the surface geology mainly consists of sedimentary rocks, with a lack of exposure of crystalline basement in many areas. Consequently, current understanding of the Yucatán subsurface is largely based on impact ejecta and drill cores recovered from the ∼200-km-diameter Chicxulub impact structure. In this study, we present the first apatite and titanite U-Pb ages for pre-impact dacitic, doleritic, and felsitic magmatic dikes preserved in Chicxulub’s peak ring sampled during the 2016 IODP-ICDP Expedition 364. Dating yielded two age groups, with Carboniferous-aged dacites (326–317 Ma) and a felsite (342.5 ± 4.3 Ma) overlapping in age with most of the granitoid basement sampled in the Expedition 364 drill core, as well as Jurassic dolerites (168–158 Ma) and a felsite (152.2 ± 11.4 Ma) that represent the first in-situ sampling of Jurassic-aged magmatic intrusions for the Yucatán Peninsula. The Nd, Sr, and Hf isotopic compositions of the pre-impact lithologies and impact melt rocks suggest that dolerites generally contributed to up to ~10 vol% of the Chicxulub impact melt that locally can exceed 40 vol%. This percentage implies that the dolerites comprised a large part of the Yucatán subsurface by volume, representing a hitherto unsampled pervasive Jurassic magmatic phase. We interpret this magmatic phase to be related to the opening of the Gulf of Mexico, representing the first physical sampling of lithologies associated with the southern extension of the opening of the Gulf of Mexico and likely constraining its onset to the Late Middle Jurassic.
Keywords: Chicxulub Impact Structure, Gulf of Mexico opening, Impact Melt Rock, Jurassic aged Pre-Impact Magmatic Dikes, geochronology, Petrography
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