首页|A low-temperature, meteoric water-dominated origin for smectitic clay minerals in the Chicxulub impact crater upper peak ring, as inferred from their oxygen and hydrogen isotope compositions

A low-temperature, meteoric water-dominated origin for smectitic clay minerals in the Chicxulub impact crater upper peak ring, as inferred from their oxygen and hydrogen isotope compositions

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  • NSTL
  • Elsevier
The peak-ring of the 66 Ma, similar to 180 km Chicxulub impact structure in the northern Yucatan peninsula and southern Gulf of Mexico was sampled during the International Ocean Discovery Program and International Continental Scientific Drilling Program (IODP-ICDP) Expedition 364 at Site M0077 (21.45 degrees N, 89.95 degrees W). Secondary clay minerals are pervasive throughout the upper peak-ring lithologies as a product of ubiquitous altered glass present throughout the impact melt and melt-bearing breccia sequence. Here we present the first detailed study of the clay mineralogy (microprobe, pXRD, spectral reflectance from 350 to 2500 nm) and isotope geochemistry (delta H-2 and delta O-18) of the <0.2 mu m size-fraction from upper peak-ring lithologies. The clay mineralogy is dominated by smectitic clay minerals, whose composition varies with stratigraphic position. Trioctahedral Mg-Fe smectite (var. saponite) is most common in Units or Subunits 2A, 2C, 3 and 4, while a section of Subunit 2B contains a more dioctahedral, Al-rich smectite. Higher porosity regions of the lower to mid, dioctahedral smectite-dominated intervals have higher delta O-18 (+14.2 to +18.6 parts per thousand) whereas intervals dominated by trioctahedral smectite have lower delta O-18 (+10.4 to +14.1 parts per thousand). The range of smectite delta H-2 (-105 to -87 parts per thousand), in comparison to that of oxygen isotopes, is proportionally much less variable and unrelated to smectite mineralogy. When combined, the oxygen and hydrogen isotope compositions of the smectitic clay minerals suggest low temperature (similar to 20 to 50 degrees C) formation from meteoric water-dominated fluids. The lower end of this temperature range is below current ambient conditions, which conceivably could suggest smectite formation before much of the overlying sedimentary rocks were deposited (similar to 56 Ma?). Calculated temperatures are generally lower than those associated with impact-generated hydrothermal alteration. Calculated delta O-18 and delta H-2 of meteoric water-dominated fluids associated with low-temperature formation of these clay minerals are lower than known for modern meteoric water in the Yucatan region. The simplest explanation for the source of these ancient fluids is meteoric water-dominated Gulf Coast brines. A more remote possibility is orogenically-driven, long-distance transport of groundwater from highlands to the east via an artesian aquifer formed in part by fractured Mesozoic rocks extending laterally beneath the impact structure.

Chicxulub impact structureStable isotope geochemistryClay mineralogySmectite mineralogyImpact-generated hydrothermal systemsGulf Coast brinesGENERATED HYDROTHERMAL SYSTEMSYUCATAN PENINSULAASTEROID IMPACTRIES CRATERDRILL COREGEOCHEMISTRYFLUIDYAXCOPOIL-1GERMANYBOREHOLE

Simpson, S. L.、Longstaffe, F. J.、Osinski, G. R.、Caudill, C. M.、Kring, D. A.

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Univ Western Ontario

Univ Space Res Assoc

2022

10.1016/j.chemgeo.2021.120639

Chemical geology

Chemical geology

EISCI
ISSN：0009-2541
年,卷(期)：2022.588
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