| Title | Secondary alteration of the impactite and mineralization in the basal Tertiary sequence, Yaxcopoil-1, Chicxulub impact crater, Mexico |
| |
| Author | Ames, D E ;
Kjarsgaard, I M; Pope, K O; Dressler, B; Pilkington, M |
| Source | Initial results of the Chicxulub Scientific Drilling Project (CSDP); Meteoritics and Planetary Science vol. 39, no. 6-7, 2004 p. 1145-1167, https://doi.org/10.1111/j.1945-5100.2004.tb01134.x |
| Links | Abstract - Résumé
|
| Image |  |
| Year | 2004 |
| Alt Series | Geological Survey of Canada, Contribution Series 2003247 |
| Publisher | Wiley-Blackwell |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Area | Mexico |
| Lat/Long WENS | -90.5000 -88.5000 22.0000 20.4167 |
| Subjects | extraterrestrial geology; geochemistry; igneous and metamorphic petrology; mineralogy; craters; meteorite craters; hydrothermal alteration; hydrothermal systems; mineralization, secondary; sea water
geochemistry; hydrothermal deposits; mafic rocks; remobilization; convection; Chicxulub impact crater |
| Illustrations | cross-sections, structural; cross-sections, stratigraphic; photomicrographs; ternary diagrams; tables; graphs |
| Abstract | The 65 Ma Chicxulub impact crater formed in the shallow coastal marine shelf of the Yucatn Platform in Mexico. Impacts into water-rich environments provide heat and geological structures that generate
and focus sub-seafloor convective hydrothermal systems. Core from the Yaxcopoil-1 (Yax-1) hole, drilled by the Chicxulub Scientific Drilling Project (CSDP), allowed testing for the presence of an impact-induced hydrothermal system by: a)
characterizing the secondary alteration of the 100 m-thick impactite sequence; and b) testing for a chemical input into the lower Tertiary sediments that would reflect aquagene hydrothermal plume deposition. Interaction of the Yax-1 impactites with
seawater is evident through redeposition of the suevites (unit 1), secondary alteration mineral assemblages, and the subaqueous depositional environment for the lower Tertiary carbonates immediately overlying the impactites.
The least-altered
silicate melt composition intersected in Yax-1 is that of a calc-alkaline basaltic andesite with 53.4-56 wt% SiO2 (volatile-free). The primary mineralogy consists of fine microlites of diopside, plagioclase (mainly Ab 47), ternary feldspar (Ab 37 to
77), and trace apatite, titanite,and zircon. The overprinting alteration mineral assemblage is characterized by Mg-saponite, Kmontmorillonite, celadonite, K-feldspar, albite, Fe-oxides, and late Ca and Mg carbonates. Mg and K metasomatism resulted
from seawater interaction with the suevitic rocks producing smectite-Kfeldspar assemblages in the absence of any mixed layer clay minerals, illite, or chlorite. Rare pyrite, sphalerite, galena, and chalcopyrite occur near the base of the impactites.
These secondary alteration minerals formed by low temperature (0-150 °C) oxidation and fixation of alkalis due to the interaction of glass-rich suevite with down-welling seawater in the outer annular trough intersected at Yax-1. The alteration
represents a cold, Mg-K-rich seawater recharge zone, possibly recharging higher temperature hydrothermal activity proposed in the central impact basin. Hydrothermal metal input into the Tertiary ocean is shown by elevated Ni, Ag, Au, Bi, and Te
concentrations in marcasite and Cd and Ga in sphalerite in the basal 25 m of the Tertiary carbonates in Yax-1. The lower Tertiary trace element signature reflects hydrothermal metal remobilization from a mafic source rock and is indicative of
hydrothermal venting of evolved seawater into the Tertiary ocean from an impactgenerated hydrothermal convective system. |
| GEOSCAN ID | 215035 |
|
|